| 1. |
- Agag, Tarek, et al.
(författare)
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Primary Amine-Functional Benzoxazine Monomers and Their Use for Amide-Containing Monomeric Benzoxazines
- 2010
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 43:6, s. 2748-2758
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Tidskriftsartikel (refereegranskat)abstract
- Amino-functional benzoxazine monomers have been successfully prepared. Several routes have been applied to incorporate amino group into benzoxazine structure. These approaches include reduction of the corresponding nitro-functional benzoxazines and deprotection of protected amino-functional benzoxazine monomers. Various approaches that allow primary amine groups to be prepared without damaging the existing benzoxazine groups have been evaluated. Tetrachlorophthalimide and trifluoroacetyl are found to be suitable protecting groups. In addition, a model compound of amide-functional benzoxazines is prepared from primary amine-functional benzoxazine. Fourier transform infrared spectroscopy (FTIR) and H-1 and C-13 nuclear magnetic resonance spectroscopy (NMR) are used to characterize the structure of the monomers. The polymerization behavior of amino-functional monomers and model compound are studied by differential scanning calorimetry (DSC).
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| 2. |
- Andrén, Oliver C. J., et al.
(författare)
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Multifunctional Poly(ethylene glycol) : Synthesis, Characterization, and Potential Applications of Dendritic-Linear-Dendritic Block Copolymer Hybrids
- 2013
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 46:10, s. 3726-3736
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Tidskriftsartikel (refereegranskat)abstract
- Emerging dendritic-linear-dendritic (DLD) hybrids that possess synergetic properties of linear and highly functional branched dendritic polymers are becoming important macromolecular scaffolds in fields ranging from biomedicine to nanotechnology. By exploiting pseudo-one-step polycondensation reactions, a facile and scalable synthetic methodology for the construction of highly functional DLDs has been developed. A library of three sets of DLDs exhibiting a hydrophilic linear PEG core with covalently attached hyperbranched bis-MPA blocks was synthesized up to the seventh generation with 256 reactive peripheral hydroxyl groups. The degree of branching for the hybrids was found between 0.40 and 0.59 with dispersities ranging from 1.03 to 1.88. The introduction of hyperbranched components resulted in control over or even full disruption of the crystallinity of the PEG. Postfunctionalizations of the peripheral hydroxyl groups with azides, allyls, and ATRP initiators yielded reactive intermediates. These intermediates were successfully assessed through UV-initiated thiol-ene coupling reactions for the synthesis of charged hybrids. ATRP of styrene from the pheriphery afforded amphiphilic macromolecules. Finally, their scaffolding capacity was evaluated for the fabrication of 3D networks, i.e, novel dendritic hydrogels and highly ordered breath figures.
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| 3. |
- Angelescu, Daniel G., et al.
(författare)
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Monte Carlo Simulations of Multigraft Homopolymers in Good Solvent
- 2014
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 47:1, s. 415-426
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Tidskriftsartikel (refereegranskat)abstract
- Multigraft polymers comprise a subclass of branched polymers where more than one side chain is attached to each node (branching point) of the main chain. We have investigated structural properties of single multigraft polymers under good solvent conditions by Monte Carlo simulations, employing a flexible bead-spring model. Beside the grafting density, denoting the linear density of grafted side chains, we have introduced the concept of branching density, denoting the linear density of nodes. At high branching density, both the branching density and the branching multiplicity controlled the structure of the side chains, whereas at lower branching density only the branching multiplicity influenced the side-chain structure. The spatial extension of the main chain and side chains as a function of side-chain length and grafting density was analyzed using scaling formalism. The dependence of the main-chain extension on side-chain length, branching density, and branching multiplicity could be collapsed on a universal curve upon relevant rescaling. Multigraft polymers with equal number of side-chain beads but unequal numbers and lengths of side chains displayed unconventional bending properties. Few and long side chains gave rise to a still relative low locally stiffness but considerable long-range rigidity, whereas more numerous and shorter side chains lead to a higher local stiffness but to a smaller long-range rigidity.
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| 4. |
- Antoni, Per, et al.
(författare)
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Pushing the Limits for Thiol-Ene and CuAAC Reactions : Synthesis of a 6th Generation Dendrimer in a Single Day
- 2010
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 43:16, s. 6625-6631
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Tidskriftsartikel (refereegranskat)abstract
- Dendrimer synthesis should not be tedious and time-consuming. By utilizing an AB(2)-CD2 approach and having orthogonal, "clickable" groups on each monomer, the time for dendrimer assembly can be drastically reduced. This was shown by preparation of a sixth generation dendrimer from starting monomer units in a single day.
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| 5. |
- Asad Ayoubi, Mehran, et al.
(författare)
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Lamellar Microdomains of Block-Copolymer-Based Ionic Supramolecules Exhibiting a Hierarchical Self-Assembly
- 2014
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 47:10, s. 3428-3435
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Tidskriftsartikel (refereegranskat)abstract
- Based on a parent diblock copolymer of poly(styrene)-b-poly(methacrylic acid), PS-b-PMAA, linear-b-amphiphilic comb (L-b-AC) ionic supramolecules [Soft Matter 2013, 9, 1540-1555] are synthesized in which the poly(methacrylate) backbone of the ionic supramolecular AC-block is neutralized by alkyl (Cn; n = 8, 12, and 16) trimethylammonium counterions (i.e., side chains) at various ion (pair) fractions X [i.e., counterion/side-chain grafting density; X = number of alkyl counterions (i.e., side chains) per acidic group of the parent PMAA block] these L-b-AC ionic supramolecules exhibit a spherical-in-lamellar hierarchical self-assembly. For these systems, (1) the effective Flory-Huggins interaction parameter between L- and AC-blocks chi'(Cn/x) was extracted, and (2) analysis of the lamellar microdomains showed that when there is an increase in X, alkyl counterion (i.e., side chain) length l(sc), or both, there is an increase in both the average interfacial area per block junction Sigma and the thickness of the microlayer of the AC-block d(Ac).
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| 6. |
- Bailey Jönsson, Johanna, et al.
(författare)
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Emulsion Condensation Polymerization in Dispersed Aqueous Media. Interfacial Reactions and Nanoparticle Formation
- 2013
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 46:22, s. 9104-9113
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Tidskriftsartikel (refereegranskat)abstract
- The polycondensation of polyesters from C-12 monomers at 95 degrees C in aqueous o/w emulsions, stabilized by acidic surfactants, has been studied in detail with a range of methods during the course of the reaction, resulting in a better understanding of the underlying reaction mechanisms. Comparisons of different surfactants, and effects of added NaCl, demonstrate that the reaction site is located at the interface between the hydrophobic core of the emulsion droplets and the surrounding water and that the reaction rate is dependent on the local concentration of oxonium ions at the reaction site. The equilibrium conversion achieved at long reaction times is, however, independent of the choice of surfactant or addition of salt, and the state of thermodynamic equilibrium is discussed thoroughly. Interestingly, a fraction of numerous "nanoparticles" (droplets in the size range <= 100 nm) have been found to develop in addition to the original fraction of droplets in the 10 mu m size range. It is suggested that these nanoparticles are formed when monomers dissolved in the aqueous phase undergo an acid-catalyzed reaction to generate water-insoluble oligomers. Once the nanoparticles are formed, the reactions in them proceed with a reaction mechanism similar to emulsion polymerization.
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| 7. |
- Beers, Keith M., et al.
(författare)
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Effect of Crystallization on Proton Transport in Model Polymer Electrolyte Membranes
- 2014
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 47:13, s. 4330-4336
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Tidskriftsartikel (refereegranskat)abstract
- Polymer electrolyte membranes with bicontinuous microphases comprising soft hydrated domains and mechanically robust hydrophobic domains are used in a wide range of electrochemical devices induding fuel cells and electrolyzers. The self-assembly, water uptake, and proton conductivity of model block copolymer electrolytes with semicrystalline hydrophobic blocks were investigated. A series of sulfonated polystyrene-block-polyethylene (PSS-PE) copolymers were synthesized to probe the interplay between crystallization, morphology, hydration, and proton transport. In block copolymer systems with amorphous hydrophobic blocks, it has been shown that higher water update and proton conductivity are obtained in low molecular weight systems. However, crystallization is known to disrupt the self-assembly of low molecular weight block copolymers. We found that this disruption results in lower water uptake and proton conductivity. Increasing molecular weight results in less morphological disruption and improvement in performance.
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| 8. |
- Chen, Yulan, et al.
(författare)
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Facile Synthesis of 3,8-Dibromo-Substituted Phenanthridine Derivatives and Their Conjugated Polymers
- 2010
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Ingår i: MACROMOLECULES. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 43:3, s. 1349-1355
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Tidskriftsartikel (refereegranskat)abstract
- We present an efficient and convenient synthesis of 3,8-dibromophenanthridine derivatives and their conjugated polymers and demonstrate that phenanthridine-containing conjugated polymers can be used as luminescent chemosensor materials. High molecular weight poly(phenanthridine-co-fluorene)s (P1, P2) and poly(phenanthridine-co-p-phenylene) (P3) were synthesized by palladium-catalyzed Suzuki-Miyaura-Schluter polycondensation (SMSPC). These phenanthridine-containing polymers are of high quantum yields in solution and show reversible optical response to protonation and deprotonation of the phenanthridine rings.
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| 9. |
- Claes, Stan, et al.
(författare)
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Free Volume Expansion of Poly[1-(trimethylsilyl)-1-propyne] Treated in Supercritical Carbon Dioxide As Revealed by Positron Annihilation Lifetime Spectroscopy
- 2011
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 44:8, s. 2766-2772
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Tidskriftsartikel (refereegranskat)abstract
- The free volume changes of poly[1-(trimethyl-silyl)-1-propyne] (PTMSP) treated in supercritical CO2 (scCO(2)) were investigated with positron annihilation lifetime spectroscopy (PALS). CO2 is known to plasticize and increase the free volume size of a broad range of polymers. In this work dense PTMSP films were treated with scCO(2) under different pressures and temperatures, resulting in the enlargement of the characteristic channel-like holes (R-3) and the larger free volume cages (R-4) up to 39% and 19%, respectively. The free volume enlargement was found to have a relaxation time of similar to 30 years. At higher temperatures (110-150 degrees C), the o-Ps intensities and gel permeation chromatography (GPC) data revealed chemical changes of the scCO(2)-treated polymer due to the onset of PTMSP's degradation. However, at lower temperatures (40-70 degrees C), significant free volume cavity size increases to 25% for R-3 and 9% for R-4 were also observed.
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| 10. |
- Deribew, Dargie, et al.
(författare)
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Crystallization-Driven Enhancement in Photovoltaic Performance through Block Copolymer Incorporation into P3HT:PCBM Blends
- 2013
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 46:8, s. 3015-3024
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Tidskriftsartikel (refereegranskat)abstract
- We report the increased crystallization of poly(3-hexylthiophene)(P3HT) in the donor−acceptor mixture of [6,6]-phenyl-C61-butyric acid methylester (PCBM) with P3HT by the addition of a block copolymer, P3HT-b-PI, where PI refers to polyisoprene. The photovoltaic performance of devices created using this blendis markedly improved by the addition of the diblock copolymer. We have characterizedthe structure of thin films of the P3HT-b-PI containing mixtures using opticalmicroscopy, scanning force microscopy, UV−vis absorption spectroscopy, neutronreflectometry, and grazing incidence X-ray diffraction (GIXD). The GIXD data providethe information on the crystallinity of the films, the absorption data were used toconfirm that the addition of the diblock was responsible for the increase in crystallization, neutron reflectometry data reveal a PCBM-rich region near the hole injection layer, and the two microscopy techniques revealed the structural effect of the crystallization at the surface of the films.
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| 11. |
- Du, Chun, et al.
(författare)
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9-Alkylidene-9H-Fluorene-Containing Polymer for High-Efficiency Polymer Solar Cells
- 2011
-
Ingår i: Macromolecules. - : American Chemical Society. - 0024-9297 .- 1520-5835. ; 44:19, s. 7617-7624
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Tidskriftsartikel (refereegranskat)abstract
- A novel donor-acceptor copolymer containing 9-alkylidene-9H-fluorene unit in the main chain, poly[9-(1-hexylheptylidene)-2,7-fluorene-alt-5, 5-(4,7-di-2-thienyl-5,6-dialkoxy-2,1,3-benzothiadiazole)] (PAFDTBT), has been synthesized and evaluated in bulk heterojunction polymer solar cells (BHJ PSCs). The polymer possesses a low band gap of 1.84 eV, a low-lying HOMO energy level (5.32 eV), and excellent solubility in common organic solvents. PSCs based on PAFDTBT and (6,6)-phenyl-C(71)-butyric add methyl ester (PC(71)BM) demonstrate a power conversion efficiency (PCE) of 6.2% with a high fill factor (FF) of 0.70, which indicates that 9-alkylidene-9H-fluorene can be a very useful building block for constructing narrow band gap conjugated polymers for high-efficiency BHJ PSCs.
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| 12. |
- Golker, Kerstin, et al.
(författare)
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Influence of composition and morphology on template recognition in molecularly imprinted polymers
- 2013
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 46:4, s. 1408-1414
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Tidskriftsartikel (refereegranskat)abstract
- A combination of theoretical and experimental studies has provided correlations between molecularly imprinted polymer composition, morphology, and recognition behavior obtained using a series of bupivacaine-imprinted methacrylic acid (MAA)–ethylene glycol dimethacrylate copolymers differing in molar ratios of the respective monomers. Results extracted from analysis of molecular dynamics (MD) trajectory data demonstrated that stability and frequency of interactions between bupivacaine and the monomers in the prepolymerization phase were strongly affected by minor changes in polymer composition, which in turn affected binding site affinity and heterogeneity of the imprinted polymers. Moreover, through the characterization of polymer morphology, we show that higher molar fractions of MAA resulted in polymeric materials with increased pore size, a feature that enhanced the binding capacity of the polymers. Furthermore, the results presented point at the strength of MD for predicting MIP-template binding capacity and affinity.
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| 13. |
- Guo, Baolin, et al.
(författare)
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Electroactive Hydrophilic Polylactide Surface by Covalent Modification with Tetraaniline
- 2012
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 45:2, s. 652-659
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Tidskriftsartikel (refereegranskat)abstract
- Covalent surface functionalization is presented as a versatile tool to increase the hydrophilicity and to introduce the electroactivity of polyester films. Acrylic acid and maleic anhydride were photografted onto a polylactide (PLA) surface with a "grafting from" method to increase the surface wettability, and the subsequent coupling of conductive aniline oligomer was used to introduce electroactivity to the PLA surface. The photopolymerization of maleic anhydride and acrylic acid and the coupling, of aniline tetramer (AT) were characterized by FT-IR, UV, and TGA. The surface morphology of the PLA surface before and after modification was examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). A medium hydrophilic surface of PLA was achieved by surface modification with maleic anhydride, acrylic acid, and AT. An electrically conductive surface was obtained after grafting with AT, and the conductivity increased with increasing AT content on the surface. The hydrophilic and electroactive surface of polyesters while retaining their bulk properties offers new possibilities in biomedical applications, such as bone, cartilage, neural, and cardiovascular tissue engineering.
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| 14. |
- Guo, Baolin, et al.
(författare)
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Enhanced Electrical Conductivity by Macromolecular Architecture : Hyperbranched Electroactive and Degradable Block Copolymers Based on Poly(epsilon-caprolactone) and Aniline Pentamer
- 2010
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 43:10, s. 4472-4480
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Tidskriftsartikel (refereegranskat)abstract
- We present macromolecular architecture design as a useful tool to enhance the conductivity of degradable polymers. Linear and hyperbranched copolymers with electrical conductivity and biodegradability were synthesized by an "A(2) + B-n (n=2, 3, 4)" strategy using carboxyl-capped aniline pen tamer (CCAP) and branched poly(epsilon-caprolactone)s (PCLs) by coupling reactions. A more hydrophilic surface and lower crystallinity of the doped emeraldine state of aniline pentamer (EM A P) copolymer was achieved compared with PCLs, and TGA results demonstrated that the CCAP contents in the copolymers were almost the same. The structure of the polymers was characterized by FT-IR. NMR, and SEC. Good electroactivity of the copolymers was confirmed by UV and cyclic voltammetry (CV), and CV showed three pairs of redox peaks. The hyperbranched copolymers had a higher conductivity than the linear ones. It is suggested that the higher conductivity of the hyperbranched copolymer is due to the ordered distribution of peripheral EMAP segments that more easily form a conductive network. Therefore, the conductivity of the polymers is improved and controlled by the macromolecular architecture.
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| 15. |
- Guo, Baolin, et al.
(författare)
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Universal Two-Step Approach to Degradable and Electroactive Block Copolymers and Networks from Combined Ring-Opening Polymerization and Post-Functionalization via Oxidative Coupling Reactions
- 2011
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 44:13, s. 5227-5236
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Tidskriftsartikel (refereegranskat)abstract
- We present a universal strategy for the facile synthesis of degradable and electroactive block copolymers and organogels (DEBCGs) based on aniline oligomers and polyesters in a two-step approach, here exemplified by the preparation of a series of DECBCGs based on aniline tetramer (AT) and poly(e-caprolactone) (PCL). Polyesters with an aniline dimer (AD) segment were first obtained by controlled ring-opening polymerization (ROP) of e-caprolactone initiated by the amine group of AD with or without 2,2-bis(epsilon-caprolactone-4-yl) propane (BCP). The postpolymerization modification via an oxidative coupling reaction between AD and a polyester was then used to form the electroactive segment AT in the copolymers or organogels. The molecular weight and conductivity of the block copolymers and organogels were controlled by the AT content. The chemical structure, electroactivity, and thermal properties of DEBCGs were investigated by FT-IR, NMR, SEC, UV, cyclic voltammetry, TGA, and DSC. Our general strategy for the synthesis of DECBCGs avoids the multiple step reactions and low efficiency involved in previous work.
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| 16. |
- Inceoglu, Sebnem, et al.
(författare)
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Effect of Supercritical Carbon Dioxide on the Thermodynamics of Model Blends of Styrene-Acrylonitrile Copolymer and Poly(methyl methacrylate) Studied by Small-Angle Neutron Scattering
- 2013
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 46:15, s. 6345-6356
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Tidskriftsartikel (refereegranskat)abstract
- Quantitative analysis of small angle neutron scattering (SANS) data from homogeneous multicomponent mixtures of supercritical carbon dioxide (scCO(2)) and two polymers is presented for the first time. The two polymers used in this study were styrene-acrylonitrile copolymer (SAN) and deuterated poly(methyl methacrylate) (dPMMA). Model polymers were used to facilitate comparisons between theory and experiment. The random phase approximation (RPA) was used to derive a simple expression to describe SANS profiles. The scCO(2)-free binary blend was studied to determine the temperature dependence of the polymer-polymer interaction parameter. scCO(2)-polymer solubility data was used to relate polymer-solvent interaction parameters. Comparisons between SANS profiles from multicomponent mixtures and the RPA expression provided an estimate of the interaction parameter between scCO(2) and PMMA, chi(13). The addition of scCO(2) at a modest pressure results in a decrease of phase separation temperature T-s by 127 K. The analysis indicates that the change in T-s is caused by an increase in chi(13) with increasing scCO(2) pressure.
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| 17. |
- Ingratta, Mark, et al.
(författare)
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Synthesis, nanostructures and properties of sulfonated poly(phenylene oxide) bearing polyfluorostyrene side chains as proton conducting membranes
- 2011
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 44:7, s. 2074-2083
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Tidskriftsartikel (refereegranskat)abstract
- Graft copolymers with ionic backbones and hydrophobic fluorinated side chains have been prepared by using lithiated poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) as a macroinitiator for anionic polymerization of 4-fluorostyrene. After grafting of the poly(4-fluorostyrene) (PFS) side chains, the PPO backbone was selectively sulfonated using trimethylsilylchlorosulfonate under mild and controlled conditions. Microscopy of solvent cast membranes revealed copolymer self-assembly into remarkably regular and well-ordered morphologies which, depending on the molecular structure, included lamellar and cylindrical arrangements of the proton conducting ionic nanophases. Thermal analysis indicated separate glass transitions of the PFS and PPO phases, and high thermal degradation temperatures of the membranes at approximately 220 and 300 °C for the H+ and the Na+ forms, respectively. The proton conductivity of fully hydrated acidic membranes was similar to that of Nafion, reaching above 0.2 S cm−1 at 120 °C. Compared at the same ion exchange capacity, the proton conductivity of the graft copolymer membranes was two times higher than that of a membrane based on an ungrafted sulfonated PPO. The study showed that it is possible to tailor and prepare proton-exchange membranes with well-ordered morphologies and high proton conductivity by employing graft copolymers with a sulfonated backbone bearing hydrophobic side chains.
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| 18. |
- Kamata, Yohei, et al.
(författare)
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Hydration and Ordering of Lamellar Block Copolymer Films under Controlled Water Vapor
- 2014
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 47:24, s. 8682-8690
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Tidskriftsartikel (refereegranskat)abstract
- Amphiphilic block copolymers within a range of volume fraction spontaneously form vesicles in aqueous solution, where a water core is enclosed by a polymer bilayer. Thin-film rehydration is a method used to produce vesicles routinely; a thin film is immersed in water, the film swells, and vesicles are formed which bleb off from the film surface. We have studied the early stages of hydration for PEOPBO block copolymer thin films under controlled water vapor conditions to understand this formation mechanism and so enable more efficient ways to encapsulate molecules using this method. Neutron and X-ray measurements show that the initial film exhibits weakly ordered structure with isotropic parallel and vertical orientation; the films initially swell and maintain the same orientation. At a critical point the layer swells rapidly and makes highly ordered lamellae structure at the same time. The lamellae are almost exclusively oriented parallel to the substrate and swell with increasing water absorption.
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| 19. |
- Knaapila, Matti, et al.
(författare)
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Measuring Structural Inhomogeneity of Conjugated Polymer at High Pressures up to 30 GPa
- 2013
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 46:20, s. 8284-8288
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Tidskriftsartikel (refereegranskat)abstract
- We present X-ray scattering data from helical poly[9,9-bis(2-ethylhexyl)-fluorene-2,7-diyl] by mapping the sample with 10 mu m spatial resolution at pressures up to 31 GPa. Neon is used as pressure transmitting medium. Reduction of torsion angle between adjacent repeats is observed during compression and found to be reversible upon decompression. Chain conformation does not depend on lateral position of sample in the pressure range from 1 to 7 GPa but depends significantly when pressure is increased from 7 to 31 GPa. Crystallite orientation does not depend on pressure or lateral position. The radiation damage is studied optically ex situ and proved to be insignificant.
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| 20. |
- Koch Money, Benson, 1980, et al.
(författare)
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Dynamics of Poly(ethylene oxide) around Its Melting Temperature
- 2013
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 1520-5835 .- 0024-9297. ; 46:17, s. 6949-6954
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Tidskriftsartikel (refereegranskat)abstract
- This study has focused on the ionic conductivity (of impurities) and the changes in relaxation behavior of semicrystalline poly(ethylene oxide) (PEO) around its melting temperature of the crystalline regions. Our main aim was to understand the implications of nucleation and growth of spherulitic structures on the general dynamical properties of the polymer chains and how these dynamical alterations affect the ionic conductivity. Impedance data have been scaled and analyzed under conductivity and modulus formalisms over wide ranges of frequency and temperature. The analysis of the scaled formalisms indicates that both the conductivity and the structural relaxation mechanisms are temperature independent above the melting point of PEO. However, below the melting, point, the slow crystallization of PEO leads to growth of spherulites and also to the formation of "interphase" regions. These morphological changes result in a hindered long-range dc conductivity, which, in turn, leads to a decoupling of the dc conductivity and the structural relaxation below the melting point of PEO.
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| 21. |
- Laiho, Ari, et al.
(författare)
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Amphiphilic Poly(3-hexylthiophene)-Based Semiconducting Copolymers for Printing of Polyelectrolyte-Gated Organic Field-Effect Transistors
- 2013
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 46:11, s. 4548-4557
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Tidskriftsartikel (refereegranskat)abstract
- Polyelectrolytes are promising electronically insulating layers for low-voltage organic field effect transistors. However, the polyelectrolyte–semiconductor interface is difficult to manufacture due to challenges in wettability. We introduce an amphiphilic semiconducting copolymer which, when spread as a thin film, can change its surface from hydrophobic to hydrophilic upon exposure to water. This peculiar wettability is exploited in the fabrication of polyelectrolyte-gated field-effect transistors operating below 0.5 V. The prepared amphiphilic semiconducting copolymer is based on a hydrophobic regioregular poly(3-hexylthiophene) (P3HT) covalently linked to a hydrophilic poly(sulfonated)-based random block. Such a copolymer is obtained in a three-step strategy combining Grignard metathesis (GRIM), atom transfer radical polymerization (ATRP) processes, and a postmodification method. The structure of the diblock copolymer was characterized using FT-IR, 1H NMR spectroscopy, and gel permeation chromatography (GPC).
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| 22. |
- Lan, Qiaofeng, et al.
(författare)
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Thermal Behavior of Poly(L-lactide) Having Low L-Isomer Content of 94% after Compressed CO2 Treatment
- 2010
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 43:20, s. 8602-8609
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Tidskriftsartikel (refereegranskat)abstract
- The effect of compressed CO2 treatment on the thermal behavior of poly(L-lactide) (PLLA) with low L-isomer content of 94% was studied by using differential scanning calorimetry (DSC) and temperature modulated DSC. It was shown that the treated samples displayed rich thermal transition signals during DSC heating, which is differ from the PLLA having high L-isomer content, including enthalpy relaxation, endothermic annealing, melting-recrystallization process, and cold crystallization. The results suggested that the crystalline phase obtained has less perfection and low crystallinity regardless of the treatment conditions because of the low crystallizability of the PLLA. This PLLA was induced to crystallize after treatment under CO2 at 2 MPa and temperature >= 65 degrees C and at pressures of 4-16 MPa and temperatures as low as 0 degrees C. At 2 MPa, the alpha crystal form is formed predominantly in the crystallized samples. The results also indicated that the ELLA-CO2 system exhibited the property of retrograde vitrification.
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| 23. |
- Li, Xuefeng, et al.
(författare)
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Fully aromatic ionomers with precisely sequenced sulfonated moieties for enhanced proton conductivity
- 2012
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 45:3, s. 1447-1459
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Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedA series of six fully aromatic ionomers with precisely sequenced sulfonated sites along the polymer chains have been designed, prepared and characterized as proton-exchange membranes. Two straight-forward and efficient synthetic strategies based on Ullmann ether reactions and a Baeyer-Villiger rearrangement were devised to obtain bisphenol monomers with four or six phenylene units linked exclusively by ether bridges to avoid transetherification reactions. Polycondensations of these bisphenol monomers with mono- or disulfonated dihalide monomers gave high molecular weight poly(arylene ether), poly(arylene ether sulfone) and polyarylene ether ketone) homopolymers having microblock-like structures with sulfonated moieties separated by monodisperse non-sulfonated oligo(ether) spacers. The nanoscale morphology and properties of solvent cast membranes were closely related to the nature of the oligo(ether) spacers. Small angle X-ray scattering (SAXS) measurements showed intense scattering and very narrow ionomer peaks with second-order features for the polymers with the six-ring spacers. This clearly indicated that the controlled ionic sequencing enabled self-assembly of ionic aggregates with a much higher degree of organization in relation to a corresponding aromatic ionomer with a statistical distribution of the sulfonate groups. At an identical acid content, the ionomers containing meta ether linkages had lower glass transition temperatures than the all-para materials, leading to a higher water uptake and proton conductivity of the former ionomers. A membrane with an ion exchange capacity (IEC) of 2.05 meq g-1 and containing exclusively para linkages reached the same level of proton conductivity as Nafion® at 100% relative humidity (RH), and also had an excellent dimensional stability in boiling water. Under reduced RH, the conductivity of this membrane greatly exceeded that of a membrane based on a statistical copolymer analogue with a similar ionic content.
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| 24. |
- Linse, Per, et al.
(författare)
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Modeling of Bottle-Brush Polymer Adsorption onto Mica and Silica Surfaces : Effect of Side-Chain Length
- 2010
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 43:4, s. 2076-2083
-
Tidskriftsartikel (refereegranskat)abstract
- Adsorption of a series of charged bottle-brush polymers with side chains of different length on solid surfaces is modeled using a lattice mean-field theory. The bottle-brush polymers are modeled Lis being composed of two types of main-chain segments: charged segments and uncharged segments with ill attached side chain. The composition variable X denotes the percentage of charged main-chain segments and ranges from X = 0 (uncharged bottle-brush polymer) to X = 100 (linear polyelectrolyte). Two types of surfaces are considered: mica-like and silica-like. The mica-like surface possesses a constant negative surface charge density and no nonelectrostatic affinity for either main-chain or side-chain segments, whereas the silica-like Surface has a constant negative surface potential and a positive affinity for the side chains of the bottle-brush polymers. With the mica-like Surface. ill low X the surface excess becomes smaller and at X >= 25 it becomes larger with increasing side-chain length. Hence, the value of X at which the surface excess displays a maximum increases with the side-chain length. However, with the silica-like Surface the surface excess increases with increasing side-chain length at all X < 100, and the maximum of the surface excess appears at X approximate to 10 independent of the side-chain length.
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| 25. |
- Linse, Per, et al.
(författare)
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Polymer Adsorption from Bulk Solution onto Planar Surfaces: Effect of Polymer Flexibility and Surface Attraction in Good Solvent
- 2010
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 43:4, s. 2054-2068
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Tidskriftsartikel (refereegranskat)abstract
- Adsorption of uncharged homopolymers of various flexibilities in good solvent onto planar surfaces Lit various polymer-surface interaction strengths have been investigated by employing a coarse-grained bead-spring polymer model using simulation techniques. The polymer flexibility ranged from fully flexible to rod-like polymers, and the adsorption strength varied from weak to strong adsorption. Equilibrium adsorption properties were determined by Monte Carlo simulations, and adsorption processes were investigated by Brownian dynamic simulations. In the latter case, file initial systems were composed of a polymer Solution and a surface separated by a slab of polymer-free solution. The equilibrium properties of the interfacial systems have been analyzed by monitoring bead and polymer density profiles, number of adsorbed beads and polymers, the components of the radius of gyration perpendicular and parallel to the surface as well as tail, loop, and train statistics. Flexible polymers adsorbed in two layers, and at ail increasing surface attraction file number of adsorbed beads and polymers increased and file adsorbed polymers become flatter, whereas rod-like polymers adsorbed ill a single and thin layer with a nematic-like order. At increasing polymer stiffness at fixed surface attraction strength, the number of adsorbed beads increased, whereas the number of adsorbed polymers. file polymer extension perpendicular to the surface, and the fraction of beads in tails all displayed nontrivial maxima Lit similar persistence length. The dynamic analysis showed that file initial adsorption was diffusion controlled, but soon became governed by the probability of a polymer to be captured by file surface attraction. Flexible polymers became flattened after attaching, but their Final relaxation mechanism involved an increased perpendicular extension with fewer adsorbed beads and longer tails driven by file Surface pressure originating from file surrounding adsorbed polymers. The stiff polymers displayed a much slower final relaxation to their equilibrium state; this relaxation predominately constituting a packing of the rocklike polymers in a 2-dimensional nematic order. Furthermore, we have defined an integration time denoting file adsorption time for adsorbed polymers to become fully integrated into the adsorbed layer. Integration times and residence times of integrated polymers became longer with increasing polymer stiffness and increasing bead-surface attraction.
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| 26. |
- Montanez, Maria I., et al.
(författare)
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Accelerated Growth of Dendrimers via Thiol-Ene and Esterification Reactions
- 2010
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 43:14, s. 6004-6013
-
Tidskriftsartikel (refereegranskat)abstract
- By taking advantage of the orthogonal nature of thiol-ene coupling and anhydride based esterification reactions, a facile and chemoselective strategy to dendritic macromolecules has been developed The ability to interchange growth steps based on thiol-ene and anhydride chemistry allows the synthesis of fifth-generation dendrimers in only five steps and under benign reaction conditions In addition, the presented coupling chemistries eliminate the traditional need for protection/deprotection steps and afford dendrimers in high yield and purity The modularity of this strategy coupled with the latent reactivity of the alkene/hydroxyl chain ends was demonstrated by using different cores (alkene and hydroxyl functional), various AB(2) and CD2 monomers and a range of chain end groups As a result, three dendritic libraries were prepared which exhibited tunability of both the chemical functionality and physical properties including the fabrication of PEG hydrogels.
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| 27. |
- Müller, Christian, et al.
(författare)
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Determination of Thermal Transition Depth Profiles in Polymer Semiconductor Films with Ellipsometry
- 2013
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Ingår i: Macromolecules. - : American Chemical Society. - 0024-9297 .- 1520-5835. ; 46:18, s. 7325-7331
-
Tidskriftsartikel (refereegranskat)abstract
- Geometric confinement and interface effects can significantly alter the thermodynamic properties of thin polymer films. Phase transition temperatures have been shown to strongly depend on film thickness below a critical thickness threshold. It has been suggested that this behavior is due to an interface-induced continuous variation in phase transition 200 temperatures throughout the depth of the films. Here we employ variable-temperature spectroscopic ellipsometry to demonstrate the existence of these depth profiles. We examine four different polymer semiconductors that are of interest for organic light-emitting diodes, solar cells, and field-effect transistors. In contrast to insulating polymers, these light-absorbing materials provide detailed information about structural changes as a function of depth due to wavelength-dependent attenuation. This concept enables us to investigate a broad range of thermodynamic processes including the glass transition, crystallization as well as crystalline and liquid-crystalline melting. In general, for the here investigated systems, higher transition temperatures are found at the free surface. Finally, the deduced profiles are used to predict the thickness dependence of the mean phase transition temperature.
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| 28. |
- Nygård, Kim, 1978, et al.
(författare)
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Size-dependent shape evolution of patterned polymer films studied in situ by phase-retrieval-based small-angle x-ray scattering
- 2012
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 45:14, s. 5798-5805
-
Tidskriftsartikel (refereegranskat)abstract
- Patterned polymer films are known to exhibit shape evolution when annealed at temperatures close to or above the glass transition temperature. Here, we employ small-angle X-ray scattering to address the size-dependent shape evolution of poly(methyl methacrylate) (PMMA) gratings obtained by thermal nanoimprint lithography. Using an iterative phase-retrieval scheme, we reconstruct the height profile of the grating in situ in a model-independent manner during a heating ramp through the glass transition. This allows us to directly observe the evolution from a trapezoidal shape, via a sinusoidal-like one, into a flat film, in agreement with ex-situ atomic force microscopy experiments. Moreover, we find the onset temperature of shape evolution to decrease monotonically with decreasing pattern size, the difference being 4 °C between gratings with periods of 240 and 80 nm. We primarily attribute the size-dependent shape evolution to a reduction in viscosity with decreasing pattern size, which is induced by either free-surface effects or surface-tension-driven non-Newtonian flow.
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| 29. |
- Olsén, Peter, et al.
(författare)
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Ring-Closing Depolymerization : A Powerful Tool for Synthesizing the Allyloxy-Functionalized Six-Membered Aliphatic Carbonate Monomer 2-Allyloxymethyl-2-ethyltrimethylene Carbonate
- 2014
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 47:18, s. 6189-6195
-
Tidskriftsartikel (refereegranskat)abstract
- Ring-dosing depolymerization is demonstrated to be a powerful synthetic methodology for the formation of six-membered functional aliphatic carbonate monomers, providing a rapid, straightforward, inexpensive, and green route for obtaining six-membered functional aliphatic carbonate monomers at a scale greater than 100g. The utility of this technique was observed via the synthesis of the allyloxy-functionalized six-membered cyclic carbonate monomer 2-allyloxymethyl-2-ethyltrimethylene carbonate (AOMEC). The synthesis was performed in a one-pot bulk reaction, starting from trimethylolpropane allyl ether, diethyl carbonate, and NaH, resulting in a final AOMEC yield of 63%. The synthetic methodology is based upon the reversible nature of this class of polymers. The anionic environment produced by NaH was observed to mediate the monomer equilibrium concentration; thus, an additional catalyst is not required to induce depolymerization. 1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD) was demonstrated to be a very active catalyst for the ring-opening polymerization (ROP) of AOMEC, resulting in a rapid (k(p)(aPP) =28.2 s(-1)) and controlled polymerization with a low dispersity D = 1.2). The availability and activity of the functionality of poly(AOMEC)s were established through subsequent postpolymerization functionalization via the UV-initiated thiol-ene chemistry of poly(AOMEC) with 1-dodecanethiol and benzophenone as a radical initiator. The functionalization proceeded with high control and with a linear relation between the molecular weight and conversion of the unsaturation, revealing the high orthogonality of the reaction and the stability of the carbonate backbone. Hence, as a synthetic methodology, depolymerization provides a straightforward and simple approach for the synthesis of the highly versatile functional carbonate AOMEC. In addition, formation of the monomer does not require any solvents, reactive ring-dosing reagents, or transition-metal-based depolymerization catalysts, thereby providing a "greener" route for obtaining functional carbonate monomers and polymers.
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| 30. |
- Olsson, Richard T., et al.
(författare)
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Extraction of Microfibrils from Bacterial Cellulose Networks for Electrospinning of Anisotropic Biohybrid Fiber Yarns
- 2010
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 43:9, s. 4201-4209
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Tidskriftsartikel (refereegranskat)abstract
- Electrospinning of uniform biohybrid fibers with concealed cellulose microfibrils (CMF) is reported as a promising and environmentally sound concept for reinforcement of polymer nonwoven fiber systems of fine dimensions. The extraction and refinement of the high-strength crystalline microfibril bundles (15-20 nm thick) from bacterial cellulose networks is presented, as well as their morphology prior to and post electrospinning. Nanofibers composed of a poly(methyl methacrylate) (PMMA) matrix with cellulose contents reaching 20 wt % were repeatedly obtained. A high deuce of dispersion of the microfibrils was obtained for a variety of CMF contents and the aggregation of the CMF was greatly suppressed as the microfibrils were aligned and rapidly sealed inside the acrylate matrix during the continuous formation of the fibers. The limited CMF aggregation up to 7 wt % was related to a suppressed phase separation caused by the rapid solidification of the polymer solutions during spinning. The fibers' diameters decreased significantly from similar to 1.8 mu m (1 wt %) to similar to 100 nm (20 wt %) with increasing cellulose contents, resulting in CMF agglomerations and percolating architectures within the acrylate host, which was consistent with microscopy, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) evaluations. The nominal content of cellulose in the fibers was assessed by Lorentzian profile fit assignment of the crystalline vs amorphous fractions of the fibers' X-ray diffractograms. TGA of fibers with low CMF content revealed that both CMF and PMMA showed a significantly improved thermal stability in the composite material. The biohybrid fibers were continuously aligned into an anisotropic nanocomposite yarns from a liquid support during spinning. The strategy described herein may allow for new mechanically robust nonwoven fiber systems, or be used as implemented on existing electrospun formulations that are lacking mechanical integrity. It is envisioned that the cellulose microfibrils may be of importance in biomedical applications where biocompatibility is a requirement.
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| 31. |
- Ossipov, Dmitri, et al.
(författare)
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Orthogonal Chemoselective Assembly of Hyaluronic Acid Networks and Nanogels for Drug Delivery
- 2013
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 46:10, s. 4105-4113
-
Tidskriftsartikel (refereegranskat)abstract
- Functionalization of hyaluronic acid (HA) with orthogonally reactive aldehyde and thiol groups permitted simultaneous bioconjugation and networking/nanostructuring of the HA chains for potential use as local and systemic delivery vehicles for medical therapies. In one experiment, the thiol-disulfide exchange reaction and carbazone chemistry were employed to construct a disulfide hydrogel matrix of HA macromolecules with the carbazone-linked poly(vinyl alcohol) prodrug of doxorubicin (PVA-DOX). In another experiment, orthogonal chemoselective reactions were utilized to prepare nanogel particles through conjugation of the polymeric PVA-DOX prodrug to HA and simultaneous attachment of hydrophobic fluorescent groups to the HA chains. The effect of the prodrug nanostructuring and functionalization with HA on the in vitro drug release and uptake by cancer cells was preliminary verified.
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| 32. |
- Pei, Aihua, et al.
(författare)
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Strong Nanocomposite Reinforcement Effects in Polyurethane Elastomer with Low Volume Fraction of Cellulose Nanocrystals
- 2011
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 44:11, s. 4422-4427
-
Tidskriftsartikel (refereegranskat)abstract
- Polyurethane/cellulose nanocrystal nanocomposites with ultrahigh tensile strength and stain-to-failure with strongly improved modulus were prepared by adding cellulose nanocrystals (CNCs) during the preparation of prepolymer. The nanostructure of this polyurethane consisted of individualized nanocellulose crystals covalently bonded and specifically associated with the hard polyurethane (PU) microdomains as characterized by Fourier transform infrared spectroscopy and transmission electron microscopy. The storage modulus and thermal stability of the nanocomposites were significantly improved as measured by dynamic mechanical analysis. This was due to a combination of CNCs reinforcement in the soft matrix and increased effective cross-link density of the elastomer network due to CNC-PU molecular interaction. Tensile test revealed that the nanocomposites have both higher tensile strength and strain-to-failure. In particular, with only 1 wt % of cellulose nanocrystals incorporated, an 8-fold increase in tensile strength and 1.3-fold increase in strain-to-failure were achieved, respectively. Such high strength indicates that CNCs orient strongly at high strains and may also induce synergistic PU orientation effects contributing to the dramatic strength enhancement. The present elastomer nanocomposite outperforms conventional rubbery materials and polyurethane nanocomposites reinforced with microcrystalline cellulose, carbon nanotubes, or nanoclays.
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| 33. |
- Rodriguez Arza, Carlos, et al.
(författare)
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Quantifying Dispersion in Graphene Oxide/Reactive Benzoxazine Monomer Nanocomposites
- 2014
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 47:11, s. 3685-3692
-
Tidskriftsartikel (refereegranskat)abstract
- Two structurally different bisbenzoxazine monomers (tBP-oda and tBP-jeff(148)) are synthesized and reinforced with graphene oxide (GO) at concentrations ranging from 0.25 to 3 wt %. Successful synthesis of the benzoxazine monomer and conversion from graphite to GO are verified by proton nuclear magnetic resonance spectroscopy (H-1 NMR), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD), respectively. Dispersibility of GO in the benzoxazine monomers prior to polymerization is studied using rheological analysis, and quantified according to the theory of fractal model of colloidal gels. The polymerization behavior of the GO/benzoxazine mixtures is studied by both differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Rheological analysis is also applied to the nanocomposite precursors. Better dispersions are achieved using tBP-oda, the benzoxazine with a high degree of aromaticity in its chemical structure. The addition of GO exhibits a negative effect on the polymerization of the two benzoxazines. The mechanical properties and the glass transition temperature T-g of GO/poly(tBP-oda) nanocomposites increases, whereas for the GO/poly(tBP-jeffi(148)) nanocomposites, the mechanical properties are moderately enhanced and T-g is reduced as a function of the GO concentration. The modifications of the mechanical and thermal properties of the nanocomposites are mainly attributed to the degree of dispersion of the GO nanosheets.
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| 34. |
- Shen, Xiantao, et al.
(författare)
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Interfacial Molecular Imprinting in Nanoparticle-Stabilized Emulsions.
- 2011
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 44:14, s. 5631-5637
-
Tidskriftsartikel (refereegranskat)abstract
- A new interfacial nano and molecular imprinting approach is developed to prepare spherical molecularly imprinted polymers with well-controlled hierarchical structures. This method is based on Pickering emulsion polymerization using template-modified colloidal particles. The interfacial imprinting is carried out in particle-stabilized oil-in-water emulsions, where the molecular template is presented on the surface of silica nanoparticles during the polymerization of the monomer phase. After polymerization, the template-modified silica nanoparticles are removed from the new spherical particles to leave tiny indentations decorated with molecularly imprinted sites. The imprinted microspheres prepared using the new interfacial nano and molecular imprinting have very interesting features: a well-controlled hierarchical structure composed of large pores decorated with easily accessible molecular binding sites, group selectivity toward a series of chemicals having a common structural moiety (epitopes), and a hydrophilic surface that enables the MIPs to be used under aqueous conditions.
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| 35. |
- Takamuku, Shogo, et al.
(författare)
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Multiblock copolymers containing highly sulfonated poly(arylene sulfone) blocks for proton conducting electrolyte membranes
- 2012
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 45:16, s. 6538-6546
-
Tidskriftsartikel (refereegranskat)abstract
- We report on multiblock copolymers consisting of highly sulfonated hydrophilic poly(arylene sulfone) (SPAS) blocks combined with hydrophobic poly(arylene ether sulfone) (PAES) blocks. Dithiol-terminated precursor blocks of sulfonated poly(arylene thioether sulfone) (SPATS) were first prepared via polycondensations involving a novel tetrasulfonated dichlorotetraphenyldisulfone monomer, followed by coupling with pentafluorophenyl end capped PAES precursor blocks under mild conditions to form SPATS-PAES block copolymers. The thioether bridges of the SPATS blocks were then selectively oxidized to obtain the SPAS-PAES copolymers with hydrophilic blocks containing exclusively sulfone bridges. Thus, the SPAS blocks were designed for high chain stiffness, stability towards desulfonation and had an ion exchange capacity (IEC) of 4.2 mequiv. g-1. Membranes of the SPAS-PAES copolymers were phase separated on the nano scale and showed an increased thermal stability and decreased water uptake in relation to the corresponding SPATS-PAES membranes. meta-Connectivity in the sulfonated blocks gave slightly higher water uptake than pure para-connectivity. At 80 ˚C and 30% relative humidity, the proton conductivity of a SPAS-PAES membrane with an IEC of 1.8 mequiv. g-1 reached 5.1 mS cm-1, which was comparable to that of Nafion® and far exceeded that of a sulfonated statistical copolymer membrane with a similar IEC. This class of block copolymers possesses very attractive properties and has great prospective to meet the demands of various electrochemical applications.
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| 36. |
- Tonpheng, Bounphanh, 1959-, et al.
(författare)
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Tensile strength and young's modulus of polyisoprene/single-wall carbon nanotube composites increased by high pressure cross-linking
- 2010
-
Ingår i: Macromolecules. - : American Chemical Society. - 0024-9297 .- 1520-5835. ; 43:18, s. 7680-7688
-
Tidskriftsartikel (refereegranskat)abstract
- High-viscosity liquid cis-1,4 polyisoprene (PI), with up to 20 wt % single-wall carbon nanotubes (SWCNTs), has been cross-linked by high pressure and high temperature (HP&HT) treatment at 513 K and pressures in the range 0.5 to 1.5 GPa to yield densified network polymer composites. A composite with 5 wt % SWCNTs showed 2.2 times higher tensile strength σUTS (σUTS = 17 MPa), 2.3 times higher Young’s modulus E (E = 220 MPa) and longer extension at break than pure PI. The improvement is attributed to SWCNT reinforcement and improved SWCNT−PI interfacial contact as a result of the HP&HT cross-linking process, and reduced brittleness despite a higher measured cross-link density than that of pure PI. The latter may originate from an effect similar to crazing, i.e., bridging of microcracks by polymer fibrils. We surmise that the higher cross-link densities of the composites are due mainly to physical cross-links/constraints caused by the SWCNT−PI interaction, which also reflects the improved interfacial contact, and that the CNTs promote material flow by disrupting an otherwise chemically cross-linked network. We also deduce that the PI density increase at HP&HT cross-linking is augmented by the presence of CNTs.
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| 37. |
- Vilaplana, Francisco, et al.
(författare)
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Two-Dimensional Size/Branch Length Distributions of a Branched Polymer
- 2010
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 43:17, s. 7321-7329
-
Tidskriftsartikel (refereegranskat)abstract
- The first two-dimensional structural distributions are reported for a hyperbranched polymer, the two dimensions being macromolecular size and individual branch length. The 2D distributions for native starch, a polymer with both short- and long-chain branched components (amylopectin and amylose), were obtained by size fractionation using size-exclusion chromatography combined with enzymatic debranching. These distributions show distinct macromolecular architectures: separate "mountains" corresponding to amylopectin and amylose and two "foothills" assigned to hybrid populations. The distributions reveal new mechanistic information on the underlying polymer synthesis. The branch-length distributions for amylopectin are independent of macromolecular size, whereas a size variation is observed for amylose. Biological imperatives in amylopectin biosynthesis force the same branching structure for all macromolecular sizes because of evolutionary pressure to provide the crystallinity indispensable for the plant survival. Amylose biosynthesis does not have such restrictive biological constraints, offering a range of branched structures throughout macromolecular sizes and revealing a previously unsuspected size dependence.
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| 38. |
- Wang, Ergang, 1981, et al.
(författare)
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Side-Chain Architectures of 2,7-Carbazole and Quinoxaline-Based Polymers for Efficient Polymer Solar Cells
- 2011
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 1520-5835 .- 0024-9297. ; 44:7, s. 2067-2073
-
Tidskriftsartikel (refereegranskat)abstract
- Three polymers bearing a common carbazole thiophene quinoxaline thiophene backbone, but different side chains, were designed and synthesized in order to investigate the effect of side chains on their photovoltaic performance. Their photophysical, electrochemical, and photovoltaic properties were investigated and compared. The polymer EWC3, with the largest amount of side chains, showed the highest power conversion efficiency of 3.7% with an open-circuit voltage (V-oc) of 0.92 V. The atomic force microscopy images of the active layers of the devices showed that the morphology was highly influenced by the choice of the solvent and processing additive. It is worth noting that polymer solar cells (PSCs) fabricated from EWC3, with branched side chains on the carbazole units, gave a much higher V-oc than the devices made from EWC1, which bears the same electron-deficient segment as EWC3 but straight side chains on carbazole units. This study offered a useful and important guideline for designing 2,7-carbazole-based polymers for high-performance PSCs.
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| 39. |
- Weiber, Annika, et al.
(författare)
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Highly proton conducting electrolyte membranes based on poly(arylene sulfone)s with tetrasulfonated segments
- 2013
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 46:9, s. 3476-3485
-
Tidskriftsartikel (refereegranskat)abstract
- A series of fully aromatic polymers having only sulfone bridges linking the aromatic rings has been synthesized via polycondensations and studied as proton-exchange membranes. Mixtures of tetrasulfonated 4,4’-bis[(4-chlorophenyl)sulfonyl]-1,1’-biphenyl (BCPSBP), non-sulfonated BCPSBP and 4,4’-thiobisbenzenethiol were copolymerized by nucleophilic aromatic substitution reactions to obtain sulfonated poly(arylene thioether sulfone)s (SPATSs) with ion exchange capacities (IECs) between 2.0 and 4.0 meq. g-1. The thioether bridges of the SPATSs were quantitatively oxidized to sulfone bridges to obtain the corresponding sulfonated poly(arylene sulfone)s (SPASs). Small angle X-ray scattering of dry SPATS and SPAS membranes showed that the tetrasulfonated segments promoted a distinct phase separation of the ionic groups already at quite low ionic contents. The SPAS polymers degraded between 300 and 340 ºC in air which was significantly above the degradation temperature of the corresponding SPATSs polymers. Moreover, SPAS membranes showed a significantly lower water uptake than the corresponding SPATS membranes. SPATS and SPAS membranes with IEC values of 2.4 and 2.2 meq. g-1, respectively, maintained high proton conductivity at low relative humidity (RH). At 30% RH and 80 ºC, these membranes reached 8 and 10 mS cm-1, respectively. The latter value coincided with that recorded for the state-of-the-art perfluorinated NRE212 membrane under the same conditions. Thus, the SPAS materials combine a straight-forward synthetic pathway with a very robust polymer structure giving high proton conductivity at reduced RH.
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| 40. |
- Werner, Erik, et al.
(författare)
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Monomer distributions and intrachain collisions of a polymer confined to a channel
- 2013
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 46:16, s. 6644-6650
-
Tidskriftsartikel (refereegranskat)abstract
- We study the conformations of a self-avoiding polymer confined to a channel by computing the cross-sectional distributions of the positions of its monomers. By means of Monte Carlo simulations for a self-avoiding, freely jointed chain, we determine how the cross-sectional distribution for a given monomer depends on its location in the polymer and how strongly this distribution is affected by self-avoidance. To this end we analyze how the frequency of intrachain collisions between monomers depends on their spatial position in the channel and on their location within the polymer. We show that most collisions occur between closely neighboring monomers. As a consequence, the collision probability depends only weakly on the spatial position of the monomers. Our results explain why the effect of self-avoidance on the monomer distributions is weaker than predicted by mean-field theory. We discuss the relevance of our results for studies of DNA conformations in nanofluidic channels.
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| 41. |
- Xu, Zhifeng, et al.
(författare)
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Boronic Acid Terminated Thermo-Responsive and Fluorogenic Polymer: Controlling Polymer Architecture for Chemical Sensing and Affinity Separation
- 2012
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 45:16, s. 6464-6470
-
Tidskriftsartikel (refereegranskat)abstract
- Thermo-responsive poly(N-isopropylacrylamide) (polyNIPAm) containing terminal boronic acid was synthesized using atom transfer radical polymerization (ATRP) in combination with Cu(I)-catalyzed alkyne-azide 1,3-dipolar cycloaddition (CuAAC) reaction. Alkyne-terminated polyNIPAm was first synthesized by ATRP using an alkyne-containing initiator. A fluorogenic boronic acid, 3-(2-azido-acetylamino)phenylboronic acid (APBA) was then linked to the polyNIPArn through CuAAC. The synthesized polymers were characterized by H-1 NMR, FT-IR, UV-vis, matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry, and turbidity measurements. The intensity of fluorescence emission of the boronic acid-terminated polyNIPAm (BA-polyNIPAm) was found to increase when increasing amount of a cis-diol compound (i.e., fructose) was added. At physiological pH value, the BA-polyNIPAm effectively bound fructose and could be easily separated from aqueous solution by raising the temperature above its lower critical solution temperature (LCST).
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| 42. |
- Young, Nicholas P., et al.
(författare)
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Thermodynamic Interactions and Phase Behavior of Multicomponent Blends Containing Supercritical Carbon Dioxide, Styrene-Acrylonitrile Random Copolymer, and Deuterated Poly(methyl methacrylate)
- 2014
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 47:22, s. 8089-8097
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Tidskriftsartikel (refereegranskat)abstract
- Small-angle neutron scattering (SANS) was used to probe the phase behavior of multicomponent mixtures of supercritical carbon dioxide (scCO(2)), styreneacrylonitrile random copolymer, and deuterated poly(methyl methacrylate). Ternary mixtures were homogeneous at low carbon dioxide pressures (PCO2) but phase separated as PCO2 was increased at constant temperature (T). Phase separation pressure was found to be a nonmonotonic function of T with a minimum at T = 60 degrees C. An expression based on the multicomponent random phase approximation was used to determine the interaction parameters between polymer and scCO(2) from a combination of SANS experiments on homogeneous ternary mixtures and measurements of scCO(2) uptake by the neat polymers. Interaction parameters that underlie the nonmonotonic phase behavior described above collapse onto a straight line when plotted as a function of scCO(2) density.
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| 43. |
- Yu, Junchun, et al.
(författare)
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A MWCNT/Polyisoprene Composite Reinforced by an Effective Load Transfer Reflected in the Extent of Polymer Coating
- 2012
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 45:6, s. 2841-2849
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Tidskriftsartikel (refereegranskat)abstract
- Tensile and microstructural properties of multiwall carbon nanotube (MWCNT)/polyisoprene (PI) composites have been investigated after cross-linking achieved purely by simultaneous high-pressure high-temperature treatment. The method enables gradual increase of the cross-link density without interference of vulcanization chemicals, and the results suggest a link between an interfacial PI layer wrapped/coated on the MWCNTs and reinforcement in carbon nanotube (CNT)/PI composites. The interfacial layer, which is augmented by high-pressure treatment, was detected indirectly in swelling experiments and also reflected in results of atomic force microscopy. The results imply more efficient load transfer and mechanical reinforcement by CNTs with improved interfacial layer and that changes in the layer can be probed by swelling measurements.
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| 44. |
- Yu, Junchun, et al.
(författare)
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High-pressure-induced microstructural evolution and enhancement of thermal properties of nylon-6
- 2010
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 43:24, s. 10512-10520
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Tidskriftsartikel (refereegranskat)abstract
- The transition behavior and thermal properties of nylon-6 at elevated pressure, p, have been established by in-situ thermal conductivity, κ, and heat capacity measurements. The glass transition temperature, Tg, of virgin nylon-6 is described well by the empirical equation Tg(p) = 319.60(1 + 1.90 p)0.24 (p in GPa and Tg in K). Moreover, isobaric heating in the 1−1.2 GPa range causes a cold-crystallization transition near 500 K. As a result, κ increased 15% whereas the heat capacity per unit volume decreased 7% slowly with time during 4 h annealing at 530 K. The transformation is associated with a significantly increased crystallinity, from 35% to 55−60%, and a pressure-induced preferred orientation and increased size for the lamellae of monoclinic α crystalline structure. This state has 8−10 K higher melting temperature and better formic acid resistance than that of virgin nylon-6. However, the results show no indication of cross-linking, as reported for similarly treated nylon-1010 and nylon-11, but instead chain scissoring.
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| 45. |
- Zhang, Junhua, et al.
(författare)
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Effect of TiO2 Formation on the Free Volume Properties of Electrospun PMMA Nanohybrids
- 2011
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 44:14, s. 5711-5721
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Tidskriftsartikel (refereegranskat)abstract
- Positron annihilation lifetime spectroscopy (PALS) has been performed on a series of PMMA nanohybrids containing nanometric TiO2, which were produced by means of different preparation methods, i.e., melt mixing, electrospinning combined with solution mixing, or in-situ sol gel growth methods, to study the effect of filler content and constituents on the free volume properties. The PMMA nanocomposites containing titania precursor or in-situformed TiO2 additives exhibit altered free volume properties compared to adding commercial TiO2 P25 fillers. The orthopositronium (o-Ps) lifetime (tau(3)) (free volume cavity size) was constant with composition in P25/PMMA nanohybrids due to the absence of interfacial interaction. However, in TiO2 precursor/PMMA composite fibers the free volume cavity size decreased substantially with hydroxyl group concentration and recovered after hydrothermal treatment. Additionally, a strong correlation between the glass transition temperature and the o-Ps lifetime in the nanohybrids was observed. These effects are caused by the hydrogen-bonding interaction between hydroxyl groups in the inorganic phase and carbonyl groups in the PMMA matrix, which concentration is dependent on the hydrothermal treatment, leading to differences in the packing of the polymer chains and a changed polymer segmental flexibility. The results also show a clear linear decrease in the o-Ps yield (I-3) with increasing P25 content of the composites. A dominant inhibition effect was observed in the TiO2 precursor/PMMA systems, caused by inhibition of positronium formation by the hydroxyl group in the titania precursor. In addition to the pronounced negative deviations of the o-Ps intensity with the concentration of hydroxyl groups in in-situ TiO2/PMMA nanohybrid fibers, a stronger inhibition efficiency of hydroxyl groups was observed than in the precursor/PMMA nanocomposite fibers.
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| 46. |
- Zhuang, Wenliu, 1979, et al.
(författare)
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Influence of Incorporating Different Electron-Rich Thiophene-Based Units on the Photovoltaic Properties of Isoindigo-Based Conjugated Polymers: An Experimental and DFT Study
- 2013
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 1520-5835 .- 0024-9297. ; 46:21, s. 8488-8499
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Tidskriftsartikel (refereegranskat)abstract
- A series of novel donor–acceptor conjugated alternating copolymers based on the isoindigo acceptor moiety have been designed, synthesized, and characterized, in order to explore the potential of isoindigo for efficient donor materials with high photovoltages in solar cells. We have systematically investigated and discussed the effect of combining different electron-rich thiophene-based units on the structural, optical, electronic, and photovoltaic properties of the resulting polymers. Morphological studies and quantum-chemical calculations are carried out to gain insights into the different properties. The power conversion efficiencies (PCEs) of the solar cells based on these polymers are increased step by step by over 3-fold through a rational structural modification. Among them, PBDTA-MIM shows a PCE of 5.4%, which is to our knowledge the best result achieved among isoindigo-based polymers for solar cells combined with PC61BM as the acceptor using the conventional device configuration. Our results further emphasize the use of isoindigo as an effective acceptor unit and highlight the importance of carefully choosing appropriate chemical structure to design efficient donor–acceptor polymers for organic solar cells. In addition, the resulting low optical gaps, the promising PCEs with PC61BM as the acceptor, and the good open-circuit voltages (up to 0.8 V) synergistically demonstrate the potential of this class of polymers as donor materials for bottom subcells in organic tandem solar cells.
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