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1.	Aasmundtveit, K.E., et al. (författare) Structural anisotropy of poly(alkylthiophene) films 2000 Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 33:8, s. 3120-3127 Tidskriftsartikel (refereegranskat)abstract The structural anisotropy of various poly(alkylthiophene) films have been studied by X-ray diffraction, using both conventional methods and synchrotron radiation at grazing incidence. Solution-cast films orient with the side chains preferably normal to the film surface, whereas spin-cast films of nonstereoregular material orient with both the main and the side chains in the film plane. For thick (10-50 µm) solution-cast films, the degree of orientation depends strongly on the solvent used for casting, and on the stereoregularity of the polymer, films of stereoregular materials being more oriented than those of nonregular materials. The most oriented nonregular films are those cast from mixtures of chloroform and tetrahydrofuran. Thin (50-500 nm) solution-cast films are more oriented than the thicker ones, and the effects of different stereoregularity or different casting solvents are small. For spin-cast films, the degree of orientation is independent of substrate and solvent. Spin-cast films of stereoregular material have two different phases: One with the side chains normal to the substrate, and another where they are parallel to the substrate. The diffraction peaks of spin-cast poly(octylthiophene) narrow considerably upon heating.
2.	Aasmundtveit, K.E., et al. (författare) Structural ordering in phenyl-substituted polythiophenes 2000 Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 33:15, s. 5481-5489 Tidskriftsartikel (refereegranskat)abstract Various substituted poly(phenylthiophene)s have been studied by X-ray diffraction. They are semicrystalline, with very different degrees of crystallinity. Those with para-substituted phenyl groups have a low degree of crystallinity, whereas those with ortho-substituted phenyl groups are more crystalline. The most crystalline materials in this study have two equally long substituents on the phenyl ring, one at the ortho position and the other at the ortho or meta position on the opposite side of the phenyl ring. Poly(3-(2,5-dioctylphenyl)thiophene) (PDOPT) was most thoroughly studied, and a structural model is proposed. The structure of PDOPT is quite different from previously studied substituted polythiophenes in that the octyl side chains are directed normal to the thiophene planes. In this way, the conjugated polymer chains are kept separated from each other. Solution-cast and spin-cast PDOPT films are anisotropic, with the octyl side chains oriented normal to the film surface in both cases. This is contrary to the situation for poly(3-alkylthiophene)s, where solution-cast and spin-cast films orient in different ways.
3.	Agag, Tarek, et al. (författare) Primary Amine-Functional Benzoxazine Monomers and Their Use for Amide-Containing Monomeric Benzoxazines 2010 Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 43:6, s. 2748-2758 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).
4.	Akinchina, Anna, et al. (författare) Monte Carlo simulations of polyion-macroion complexes. 1. Equal absolute polyion and macroion charges 2002 Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 35:13, s. 5183-5193 Tidskriftsartikel (refereegranskat)abstract Intermolecular structures of complexes formed between a charged polymer and a spherical and oppositely charged macroion have been studied by employing the primitive model solved by Monte Carlo simulations. The strong-complex case involving a polyion and a macroion with equal absolute charges and without small ions was considered. The influence of the polyion flexibility with a bare persistence length ranging from 7 to 1000 Angstrom for four different systems characterized by different polyion linear charge densities and macroion sizes has been examined. Radial distributions, polyion bead complexation probabilities, loop, tail, and train characteristics, and energetic analysis have been performed. The strongest and most compact complex, involving a collapsed polyion wrapping the macroion, was formed for a semiflexible chain. As the stiffness was increased, this state was transformed into a range of different structures comprising "tennis ball seam"-like, solenoid, multiloop ("rosette"), and single-loop arrangements as well as structures involving only a single polyion-macroion contact region.
5.	Algers, John, et al. (författare) Free volume and density gradients of amorphous polymer surfaces as determined by use of a pulsed low-energy positron lifetime beam and PVT data 2004 Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 37:11, s. 4201-4210 Tidskriftsartikel (refereegranskat)abstract Density gradient widths at the polymer-vacuum surfaces of poly(methyl methacrylate), styrene-co-acrylonitrile, and styrene-co-maleic anhydride were quantified to 2, 5, and 4 rim, respectively, by use of a pulsed low-energy positron lifetime beam and to approximately 1.5 nm for all three polymers on the basis of theoretical predictions from pressure-volume-temperature (PVT) data, making use of the Cahn-Hilliard theory of inhomogeneous systems in conjunction with the Sanchez-Lacombe lattice fluid theory. Excellent agreement between the two methods was found for the homopolymer, whereas for the copolymers, the former method gave larger density gradient widths, a result attributed to the surface orientation of the less polar polymer segments, which the theoretical predictions did not take into account. As has been previously proposed, the discrepancy between the depth ranges of the surface effects on density and the glass transition temperature (T-g) is suggested to result from a coupling between the dynamics of adjoining polymer segments, canceling a direct relationship between local density profile rho(z) and local T-g(z) as a function of distance z from the free surface.
6.	Algers, John, et al. (författare) Free volume determination of azobenzene-PMMA copolymer by a pulsed low-energy positron lifetime beam with in-situ UV illumination 2004 Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 37:21, s. 8035-8042 Tidskriftsartikel (refereegranskat)abstract The free volume properties of a poly(methyl methacrylate)-azobenzene copolymer were for the first time directly probed by use of a low-energy positron lifetime beam with in-situ excitation capabilities, showing that the free volume cavity size was not appreciably influenced by photoisomerization and thermal isomerization in the temperature range 34-180 degreesC. lsomerization is therefore suggested to occur without any molecular rearrangement of the glassy polymer matrix, which would also account for the lack of any shift to shorter wavelengths for the photoisomerization occurring in a glassy polymer in comparison to a chloroform solution. A decrease in the thermal isomerization rate at room temperature caused by the glassy polymer is explained in terms of a model in which only a fraction of the azobenzene is free to isomerize. The cis-azobenzene was found to be an efficient inhibitor of positronium formation, which enabled measurements of thermal isomerization rates and changes in the steady-state concentration of cis-azobenzene for an illuminated sample as a function of temperature.
7.	Alizadehheidari, Mohammadreza, 1987, et al. (författare) Nanoconfined Circular and Linear DNA: Equilibrium Conformations and Unfolding Kinetics 2015 Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 48:3, s. 871-878 Tidskriftsartikel (refereegranskat)abstract Studies of circular DNA confined to nanofluidic channels are relevant both from a fundamental polymer-physics perspective and due to the importance of circular DNA molecules in vivo. We here observe the unfolding of confined DNA from the circular to linear configuration as a light-induced double-strand break occurs, characterize the dynamics, and compare the equilibrium conformational statistics of linear and circular configurations. This is important because it allows us to determine to what extent existing statistical theories describe the extension of confined circular DNA. We find that the ratio of the extensions of confined linear and circular DNA configurations increases as the buffer concentration decreases. The experimental results fall between theoretical predictions for the extended de Gennes regime at weaker confinement and the Odijk regime at stronger confinement. We show that it is possible to directly distinguish between circular and linear DNA molecules by measuring the emission intensity from the DNA. Finally, we determine the rate of unfolding and show that this rate is larger for more confined DNA, possibly reflecting the corresponding larger difference in entropy between the circular and linear configurations.
8.	Allushi, Andrit, et al. (författare) Polyfluorenes Bearing N,N-Dimethylpiperidinium Cations on Short Spacers for Durable Anion Exchange Membranes 2023 Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 56:3, s. 1165-1176 Tidskriftsartikel (refereegranskat)abstract Alicyclic quaternary ammonium cations having all the β-protons in a strain-free ring structure are in general highly base resistant, and are thus very attractive to employ for anion exchange membrane (AEM) applications. However, tethering cations such as N,N-dimethylpiperidinium (DMP) to polymer backbones without introducing any weak links is quite challenging. In the present study, we have attached pairs of piperidine rings in their 4-position to fluorene and 2,7-diphenylfluorene via methylene bridges using straightforward SN2 reactions. These fluorenes were subsequently utilized as monomers in polyhydroxyalkylations to prepare poly(fluorene alkylene)s with different contents of the piperidine groups. AEMs were cast after quaternizing the piperidine groups to introduce DMP and spirocyclic 6-azonia-spiro-[5,5]undecane-6-ium (ASU) cations, respectively. The AEMs reached very high hydroxide ion conductivities, 100-156 mS cm-1 at 80 ºC, in the ion exchange capacity (IEC) range 1.8-2.4 mequiv. g-1. X-ray scattering showed ionomer peaks indicating ionic clustering with a characteristic distance d = 2.0-2.9 nm depending on IEC. The AEMs displayed high thermal stability, up to ~250 ºC, and 1H NMR data indicated no degradation after storage in 5 M aq. NaOH during 168 h at 90 ºC. However, degradation started under very severe conditions (10 M, 90 °C) with ~75% of the total ionic loss in all the AEMs assigned to Hofmann β-elimination. The overall results show that fluorene-based AEMs carrying DMP and ASU cations via methylene bridges display an attractive combination of ionic phase separation, thermal and chemical stability, and hydroxide conductivity.
9.	Andersson, Mats R., et al. (författare) Electroluminescence from Substituted Poly(thiophenes) : From Blue to Near-Infrared 1995 Ingår i: Macromolecules. - : American Chemical Society. - 0024-9297 .- 1520-5835. ; 28:22, s. 7525-7529 Tidskriftsartikel (refereegranskat)abstract We report a systematic approach to the control of the conjugation length along the poly(thiophene) backbone. The planarity of the main chain can be permanently modified by altering the pattern of substitution and character of the substituents on the poly(thiophene) chain, and the conjugation length is thus modified. We obtain blue, green, orange, red, and near-infrared electroluminescence from four chemically distinct poly(thiophenes). The external quantum efficiencies are in the range of 0.01-0.6%.
10.	Andersson, Mats R., et al. (författare) Regioselective polymerization of 3-(4-octylphenyl)thiophene with FeCl3 1994 Ingår i: Macromolecules. - : American Chemical Society. - 0024-9297 .- 1520-5835. ; 27:22, s. 6503-6506 Tidskriftsartikel (refereegranskat)abstract We have shown that it is possible to regioselectively polymerize 3-(4-octylphenyl) thiophene with FeCl3. Adding FeCl3 slowly to the monomer leads to a soft and therefore regioselective polymerization. The head-to-tail content was determined by H-1 NMR to be 94 +/- 2%. Thin films of the polymer treated with chloroform vapor have an absorption maximum at 602 nm (2.06 eV) with clear vibronic fine structure. Free standing films have a conductivity of 4 S/cm, which is 100 times higher than for earlier prepared poly(3-(4-octylphenyl)thiophene). A mechanism for the regioregular polymerization is also proposed.
11.	Andersson, S. Peter, et al. (författare) Relaxation Studies of Poly(propylene glycol) under High Pressure 1998 Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 31:9, s. 2999-3006 Tidskriftsartikel (refereegranskat)abstract The effect of pressure on the relaxation processes in poly(propylene glycol) of number-average molecular weights 400 and 4000 g mol-1 (PPG-400 and PPG-4000) has been investigated using dielectric spectroscopy as well as thermal conductivity and heat capacity measurements. The relaxations associated with segmental motions within the polymer chain (α relaxation) and whole chain motions (α' relaxation) have been studied in the temperature range 200-400 K for pressures up to 2 GPa. The two processes display slightly different sensitivities to pressure, and as a consequence, are better separated at high pressures. As a result, high-pressure data exhibit the α' relaxation also in PPG-400, whereas previous investigations at atmospheric pressure have detected it only in PPG of molecular weights above about 1000 g mol-1. At atmospheric pressure, the values for (∂T/∂p)τ=1s of the alpha relaxation are, respectively, 140 and 192 K GPa-1 for PPG-400 and PPG-4000, where τ is the relaxation time. Because of the difference in (∂T/∂p)τ, the relaxation of the α motions and therefore the glass-transition temperature exhibits a more significant dependence on molecular weight at high pressures. At 295 K and 0.3 GPa, the activation volumes for the α and α' processes of PPG-4000 are about the same (approximate to 45 cm3 mol-1). At the same conditions, the activation volume for the α process of PPG-400 is about half of that for PPG-4000. An analysis of the α relaxation in terms of the strong-fragility classification shows that the degree of fragility of both PPG-400 and PPG-4000 increases slightly with increasing pressure.
12.	Andrén, Oliver C. J., et al. (författare) Multifunctional Poly(ethylene glycol) : Synthesis, Characterization, and Potential Applications of Dendritic-Linear-Dendritic Block Copolymer Hybrids 2013 Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 46:10, s. 3726-3736 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.
13.	Angelescu, Daniel G., et al. (författare) Monte Carlo Simulations of Multigraft Homopolymers in Good Solvent 2014 Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 47:1, s. 415-426 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.
14.	Antlauf, Mathis, et al. (författare) Thermal Conductivity of Porous and Dense Networks of Cellulose Nanocrystals 2022 Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 55:13, s. 5326-5331 Tidskriftsartikel (refereegranskat)abstract Cellulose is a crystalline polymer with intriguing, amorphous-like, temperature dependence of thermal conductivity κ. To determine its origin, we have studied κ of cellulose nanocrystals (CNCs) derived from cotton by sulfuric acid hydrolysis, in both porous and nonporous states by pressure densification; κ increases weakly with increasing temperature and density, like in a fully amorphous material, and it is remarkably similar to that of cellulose fibers (CFs) and cellulose nanofibers (CNFs). For a powder derived from a natural material, like cellulose, amorphous-like κ may originate from poor thermal contact between particles or a high amorphous content, but the latter is not the case for CNCs. Moreover, the amorphous-like behavior is unaffected by densification and, therefore, improved thermal contacts. Instead, we attribute the behavior to CNCs' nanometer-sized fibrils, which limit the phonon mean free path to a few nanometers in a network of randomly oriented CNCs. This explains why κ is essentially the same in networks of CNCs, CFs, and CNFs, which are materials with the same structural unit-elementary fibrils of 3-5 nm in diameter. We obtain κ = (0.60 ± 0.01) W m-1 K-1 for a nonporous network of randomly oriented CNCs at 295 K and atmospheric pressure, and κ increases by only 14% GPa-1, which is unusually weak for a polymer. By using a model for such a network, we find κ = 1.9 W m-1 K-1 along a CNC and argue that this is a good estimate also along a CNF and a CF at room temperature.
15.	Antoni, Per, et al. (författare) Pushing the Limits for Thiol-Ene and CuAAC Reactions : Synthesis of a 6th Generation Dendrimer in a Single Day 2010 Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 43:16, s. 6625-6631 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.
16.	Aronsson, Christopher, et al. (författare) Zinc-Triggered Hierarchical Self-Assembly of Fibrous Helix-Loop-Helix Peptide Superstructures for Controlled Encapsulation and Release 2016 Ingår i: Macromolecules. - : AMER CHEMICAL SOC. - 0024-9297 .- 1520-5835. ; 49:18, s. 6997-7003 Tidskriftsartikel (refereegranskat)abstract We demonstrate a novel route for hierarchical self-assembly of sub-micrometer-sized peptide superstructures that respond to subtle changes in Zn2+ concentration. The self-assembly process is triggered by a specific folding-dependent coordination of Zn2+ by a de novo designed nonlinear helix-loop-helix peptide, resulting in a propagating fiber formation and formation of spherical superstructures. The superstructures further form larger assemblies that can be completely disassembled upon removal of Zn2+ or degradation of the nonlinear peptide. This flexible and reversible assembly strategy of the superstructures enables facile encapsulation of nanoparticles and drugs that can be released by means of different stimuli.
17.	Asad Ayoubi, Mehran, et al. (författare) Lamellar Microdomains of Block-Copolymer-Based Ionic Supramolecules Exhibiting a Hierarchical Self-Assembly 2014 Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 47:10, s. 3428-3435 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).
18.	Asplund, Basse, et al. (författare) Variable Hard Segment Length in Poly(urethane urea) through Excess of Diisocyanate and Vapor Phase Addition of Water 2006 Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 39, s. 4380-4385 Tidskriftsartikel (refereegranskat)abstract Poly(urethane urea)s with hard segments derived only from diisocyanate linked via urea linkages were synthesized using a new and simple one-pot method. The creation of urea linkages were done via creating the amine in situ by adding water in vapor phase slowly and continuously. This synthesis method eliminates the tedious control to approach stoichiometry, is less sensitive to impurities, involves no intermediate isolation steps, and does not involve any chain extender. A study using a two-armed poly(-caprolactone) as soft segment and methyl 2,6-diisocyantohexanoate (LDI) as the hard segment was performed. The length of the hard segment was varied from 4.8 to 11.6 LDI units. Stress-strain measurements showed an increase in elastic modulus, 146 to 235 MPa, when increasing the hard segment length, while the elongation at break decreased, 980 to 548%. IR spectroscopy showed an increase in hydrogen bonding when increasing the hard segment length. The synthesis was also shown to be applicable to common diisocyanates such as HDI, TDI, and MDI.
19.	Atthoff, Björn, et al. (författare) Biodegradable Ionomers 2006 Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 39:11, s. 3907-3913 Tidskriftsartikel (refereegranskat)abstract Several telechelic anionic or cationic ionomers were synthesized starting from poly(trimethylene carbonate) diols (PTMC) of different molecular weight, ranging from 1000 to 12 000 g/mol. In the synthesis of the anionomer, addition of sulfur trioxide trimethylene complex to the PTMC end-group hydroxyls and subsequent ion exchange afforded a disulfate monoester sodium salt. The cationomer was synthesized in two steps. Acylation of the PTMC diol using 4-chlorobuturyl chloride was followed by displacement of the alkyl chloride with trimethylamine to give a quaternary ammonium salt. These ionomers showed excellent swelling properties, up to around 500% in H2O, while the unfunctionlized PTMC did not swell at all. The lowest molecular weight ionomers were soluble in both water and chloroform. The physical properties of the ionomers were analyzed with oscillating rheological experiments. Interestingly, the ionomers displayed "rubbery plateau". The mechanical and swelling properties may be linked to phase separation resulting in ionic aggregates within the bulk, which may function as physical cross-links. At ambient temperatures, the PTMC starting material behaved like a highly viscous fluid, while the ionomers behaved as elastomers. In a hydrophilic environment, the ionomers displayed a surface rearrangement making the surface of the ionomer hydrophilic by allowing the ionic end groups to appear at the water ionomer interface. In air or vacuum all the ionic groups were found in the bulk of the material as analyzed by XPS or contact angle measurements. Finally, we showed that with the specific ionic groups it was possible to complex specific molecules to the ionomers.
20.	Bailey Jönsson, Johanna, et al. (författare) Emulsion Condensation Polymerization in Dispersed Aqueous Media. Interfacial Reactions and Nanoparticle Formation 2013 Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 46:22, s. 9104-9113 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.
21.	Barrau, Sophie, et al. (författare) Nanomorphology of Bulk Heterojunction Organic Solar Cells in 2D and 3D Correlated to Photovoltaic Performance 2009 Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 42:13, s. 4646-4650 Tidskriftsartikel (refereegranskat)abstract Control of the nanoscale morphology of the donor-acceptor material blends inorganic solar Cells is critical for optimizing the photovoltaic performances. The influence of intrinsic (acceptor materials) and extrinsic (donor:acceptor weight ratio, substrate, solvent) parameters was investigated, by atomic force microscopy (AFM) and electron tomography (ET), on the nanoscale phase separation of blends of a low-band-gap alternating polyfluorene copolymers (APFO-Green9) with [6,6]-phenyl-C-71-butyric acid methyl ester ([70]PCBM). The photovoltaic performances display an optimal efficiency for the device elaborated with a 1:3 APFO-Green polymer:[70][PCBM weight ratio and spin-coated from chloroform solution. The associated active layer morphology presents small phase-separated domains which is a good balance between as a large interfacial donor-acceptor area and Continuous paths of the donor and acceptor phases to the electrodes.
22.	Beers, Keith M., et al. (författare) Effect of Crystallization on Proton Transport in Model Polymer Electrolyte Membranes 2014 Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 47:13, s. 4330-4336 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.
23.	Benkoski, JJ, et al. (författare) Light-activated desorption of photoactive polyelectrolytes from supported lipid bilayers 2005 Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 38:9, s. 3852-3860 Tidskriftsartikel (refereegranskat)abstract Phospholipid vesicles and supported bilayers have emerged as a promising platform for the development of biorecognition devices. To expand the capabilities of such biochips, it becomes desirable to direct and control the assembly of lipid structures into more sophisticated architectures. As one step toward this goal, we demonstrate the photoregulated desorption of a new class of polymer from lipid bilayers. The neutral, hydrophobic polymer resides within the bilayer under mild pH and ambient conditions. However, it contains side groups that can undergo excited state proton transfer (ESPT). The polymer therefore behaves as a polyelectrolyte when exposed to IN light. With the ensuing increase in hydrophilicity, the molecule is spontaneously ejected from the bilayer. Quartz crystal microbalance measurements with dissipation monitoring (QCM-D) have recorded this process and have shown that a rapid buffer exchange during light exposure results in efficient removal of the polymer from the system. Three polymers were tested in all: a polyanion, a polyeation, and a polyzwitterion. A one-step approach to the synthesis of the monomer, performed under relatively mild reaction conditions, made it possible to synthesize each polymer in one step.
24.	Bergenudd, Helena, et al. (författare) Solvent Effects on ATRP of Oligo(ethylene glycol) Methacrylate. Exploring the Limits of Control 2009 Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 42:9, s. 3302-3308 Tidskriftsartikel (refereegranskat)abstract Five copper complexes in combination with six monomer-solvent mixtures have been used to investigate the solvent effects oil ATRP of oligo(ethylene glycol) methacrylate (OEGMA). The redox properties of the copper complexes in OEGMA-solvent mixtures and the apparent rate constants (k(p)(app)) for ATRP of OEGMA were correlated to the degree of control over the polymerizations. Based on this correlation, a general discussion of the limits of control in ATRIP is carried out. One of the key parameters for control in ATRP is the propagation rate constant, making the choice of monomer essential for the design of ail ATRP system. Also, the solvent effects oil the ATRP equilibrium constant (K-ATRP) affect the limit of control (i.e., the apparent rate constant above which control is lost). The choice of copper complex is also more important than the choice of solvent for the design of a well-controlled ATRP system.
25.	Bergfeldt, K, et al. (författare) Phase Separation Phenomena and Viscosity Enhancements in 1995 Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 28:9, s. 3360-3370 Tidskriftsartikel (refereegranskat)abstract Interactions between poly(styrenesu1fonate) (PSS) and poly(acry1ic acid) (PA) in aqueous solution have been studied, with and without added salt, and at various degrees of neutralization (a) of PA. Equilibrium phase diagrams have been determined, and the viscosities of monophasic mixtures have been measured. Both types of experiments reveal striking effects of a on the PA-PSS interactions. Salt-free mixtures with fully or partially neutralized poly(acry1ic acid) phase separate segregatively, except at very low a where, instead, an association between PA and PSS occurs. The association is evidenced by a dramatically increased viscosity, relative to solutions of PA or PSS alone, in semidilute mixtures. Addition of salt (1 M NaC1) results in an increased two-phase area at all a, and in the appearance of an associative phase separation for non-neutralized PA. The qualitative phase behavior observed in the presence of salt can be generated by calculations using the Flory-Huggins theory, if it is assumed that both the PSS-PA and the PA-solvent interactions change monotonically with a in a specified fashion. All experimental observations, and the theoretical modeling, suggest that the effective PA-PSS interaction changes (over a narrow interval of a) from an attraction at very low a to a repulsion at higher a.

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