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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.
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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.
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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).
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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.
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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.
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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.
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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.
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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.
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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%.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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).
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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.
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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.
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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.
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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.
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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.
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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.
  •  
26.
  •  
27.
  • Björling, Mikael, et al. (författare)
  • An NMR Self-Diffusion Study of the Interaction between Sodium Hyaluronate and Tetradecyltrimethylammonium Bromide
  • 1995
  • Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 28:20, s. 6970-6975
  • Tidskriftsartikel (refereegranskat)abstract
    • A decrease of the NMR self-diffusion coefficient of sodium hyaluronate (NaHy) upon increasing tetradecyltrimethylammonium bromide (TTAB) concentration in 202 mM NaCl (just enough to attain single phase conditions irrespective of the TTAB concentration) is interpreted in terms of the formation of NaHy–TTAB complexes containing several NaHy chains. The complexes are judged to be induced by multiple-site electrostatic condensation of TTAB micelles onto the Hy chains. Thus, the TTAB micelles may act as bridging points between, and within, the NaHy chains. For a 1% wt NaHy solution, at 202 mM NaCl, the fraction of adsorbed TTAB has a maximum at 10 mM TTAB where an estimated 54% of all the added TTAB is bound. At 70 mM TTAB, the fraction of bound TTAB has decreased to 42%. The decrease of the binding constant with increasing TTAB concentration is attributed to a more efficient electrostatic screening; i.e., the ionic strength (due to uncondensed species) increases. The observed NaHy–TTAB complexes are likely to be precursors of the precipitated phase formed at lower salt concentrations.
  •  
28.
  • Björling, Mikael (författare)
  • Interaction between Surfaces with Attached Poly(ethylene oxide) Chains
  • 1992
  • Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 25:15, s. 3956-3970
  • Tidskriftsartikel (refereegranskat)abstract
    • The paper presents a self-consistent mean-field lattice theory of the Scheutjens-Fleer type where segments may adapt to temperature and the local environment by changing their distribution among internal states. Some new features are introduced in the theoretical treatment of incompressible systems, and it is demonstrated how the chemical potential may be calculated without reference to a bulk system. The theory is applied to make a qualitative prediction for the interaction between surfaces with grafted poly-(ethylene oxide), or PEO, chains. A simple two-state model for the PEO segments is used. The attractive force between the PEO-covered surfaces in water is predicted to be related to the temperature-dependent solubility of PEO in water. The contributions to the force are illustrated by simple examples. The attractive force does not change monotonically upon changing the graft density. At low coverages a strong bridging attraction is predicted if the surfaces are hydrophobic. As the surfaces become more polar, repulsion sets in at a larger separation and the overall attraction becomes less strong. A calculated, closed, solubility gap for a crude model of micelles of nonionic surfactants is presented.
  •  
29.
  • Björling, Mikael (författare)
  • Using end-confined chains to model end-absorbing, triblock copolymers : 1. Analytical approach
  • 1998
  • Ingår i: Macromolecules. - 0024-9297 .- 1520-5835. ; 31:25, s. 9026-9032
  • Tidskriftsartikel (refereegranskat)abstract
    • The bridging attraction, mediated by associative, triblock copolymers with insoluble end blocks and a soluble spacer block, is analyzed using scaling arguments and analytical methods. Adsorbing these associative polymers (APs) onto a single surface, the approach of another, bare, surface results in a strong bridging attraction. When both slit surfaces bear adsorbed APs, the bridging attraction is much weaker. The main contribution is an entropic gain since bridge formation decreases the monomer number density in the crowded region near the surface.
  •  
30.
  • Björling, Mikael, et al. (författare)
  • Using end-confined chains to model end-absorbing, triblock copolymers : 2. Numerical approach
  • 1998
  • Ingår i: Macromolecules. - 0024-9297 .- 1520-5835. ; 31:25, s. 9033-9043
  • Tidskriftsartikel (refereegranskat)abstract
    • The bridging attraction mediated by end-absorbing, triblock copolymers in a good solvent is analyzed using numerical methods and compared to analytical results. Good agreement is found. The main deviations may be attributed to the neglect of thermal fluctuations in the extension of the loops at the brush edge in the analytical treatment. With a suitable choice of "natural" units, the numerical results for the bridging probability and the free energy of interaction per chain collapse onto universal master curves in the two arrangements considered: symmetric and asymmetric adsorption of associative polymers (APs) on the surfaces of a planar slit.
  •  
31.
  • Boye, Susanne, et al. (författare)
  • From 1D Rods to 3D Networks: A Biohybrid Topological Diversity Investigated by Asymmetrical Flow Field-Flow Fractionation
  • 2015
  • Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 48:13, s. 4607-4619
  • Tidskriftsartikel (refereegranskat)abstract
    • Biohybrid structures formed by noncovalent interaction between avidin as a bridging unit and biotinylated glycodendrimers based on poly(propyleneimine) (GD-B) have potential for biomedical application. Therefore, an exact knowledge about molar mass, dispersity, size, shape, and molecular structure is required. Asymmetrical flow field-flow fractionation (AF4) was applied to separate pure and assembled macromolecules according to their diffusion coefficients. The complex biohybrid structures consist of single components (avidin, differently valent GD-B) and nanostructures. These nanostructures were systematically studied depending on the degree of biotinylation and ligand-receptor stoichiometry by AF4 in combination with dynamic and static light scattering detection. This enables the quantification of composition and calculation of molar masses and radii, which were used to analyze scaling properties and apparent density of the formed structures. These data are compared to hydrodynamic radii obtained by applying the retention theory to the AF4 data. It is shown that depending on their architecture the molecular shape of biohybrid structures is changed from rod-like to spherical toward network-like behavior.
  •  
32.
  •  
33.
  • Brett, Calvin, et al. (författare)
  • Water-Induced Structural Rearrangements on the Nanoscale in Ultrathin Nanocellulose Films
  • 2019
  • Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 52:12, s. 4721-4728
  • Tidskriftsartikel (refereegranskat)abstract
    • Many nanoscale biopolymer building blocks with defect-free molecular structure and exceptional mechanical properties have the potential to surpass the performance of existing fossil-based materials with respect to barrier properties, load-bearing substrates for advanced functionalities, as well as light-weight construction. Comprehension and control of performance variations of macroscopic biopolymer materials caused by humidity-driven structural changes at the nanoscale are imperative and challenging. A long-lasting challenge is the interaction with water molecules causing reversible changes in the intrinsic molecular structures that adversely affects the macroscale performance. Using in situ advanced X-ray and neutron scattering techniques, we reveal the structural rearrangements at the nanoscale in ultrathin nanocellulose films with humidity variations. These reversible rearrangements are then correlated with wettability that can be tuned. The results and methodology have general implications not only on the performance of cellulose-based materials but also for hierarchical materials fabricated with other organic and inorganic moisture-sensitive building blocks.
  •  
34.
  • Brouzet, Christophe, et al. (författare)
  • Characterizing the Orientational and Network Dynamics of Polydisperse Nanofibers on the Nanoscale
  • 2019
  • Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 52:6, s. 2286-2295
  • Tidskriftsartikel (refereegranskat)abstract
    • Polydisperse fiber networks are the basis of many natural and manufactured structures, ranging from high-performance biobased materials to components of living cells and tissues. The formation and behavior of such networks are given by fiber properties such as length and stiffness as well as the number density and fiber-fiber interactions. Studies of fiber network behavior, such as connectivity or rigidity thresholds, typically assume monodisperse fiber lengths and isotropic fiber orientation distributions, specifically for nano scale fibers, where the methods providing time-resolved measurements are limited. Using birefringence measurements in a microfluidic flow-focusing channel combined with a flow stop procedure, we here propose a methodology allowing investigations of length-dependent rotational dynamics of nanoscale polydisperse fiber suspensions, including the effects of initial nonisotropic orientation distributions. Transition from rotational mobility to rigidity at entanglement thresholds is specifically addressed for a number of nanocellulose suspensions, which are used as model nanofiber systems. The results show that the proposed method allows the characterization of the subtle interplay between Brownian diffusion and nanoparticle alignment on network dynamics.
  •  
35.
  • Busson, P., et al. (författare)
  • Ferroelectric liquid crystalline dendrimers : Synthesis, thermal behavior, and electrooptical characterization
  • 2001
  • Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 34:5, s. 1221-1229
  • Tidskriftsartikel (refereegranskat)abstract
    • The preparation and characterization of a series of novel ferroelectric liquid crystalline dendrimers are presented. End-capping of 1-, 2-, and 3-generation dendrimers based on 2,2-bis(hydroxymethyl)propionic acid with mesogens gave surface-functionalized liquid crystalline compounds with 6, 12, and 24 mesogen-containing units, respectively. 4 -((R)-1-Methylheptyloxy)phenyl 4-(4 '-[10(hydroxycarbonyl)decyloxyl phenyl)benzoate was synthesized and used as a mesogen-containing unit. The purity and structure of each compound were determined by H-1 NMR spectroscopy, size exclusion chromatography, and elemental analysis. Differential scanning calorimetry and optical microscopy were used to investigate the mesomorphic properties of the mesogen-functionalized dendrimers. The materials displayed a variety of mesophases, including the smectic C* phase. All the liquid crystalline dendrimers showed ferroelectricity, and tilt angle and spontaneous polarization measurements were performed. The obtained results show that the ferroelectric properties of the materials are independent of the generation number of the dendritic scaffold.
  •  
36.
  • Busson, P., et al. (författare)
  • Preparation of mesogen-functionalized dendrimers for second-order nonlinear optics
  • 2002
  • Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 35:5, s. 1663-1671
  • Tidskriftsartikel (refereegranskat)abstract
    • Liquid crystalline dendrimers with peripheral mesogen-containing units have been prepared. Multistep synthesis with several selective reactions was used in the preparation of the mesogen-containing molecules, 4-[10-(hydroxycarbonyl)decyloxy]phenyl 4-[4'-(2-(R)-octyloxy)-3'-nitrophenyl]benzo ate and 4-[10-(hydroxycarbonyl)decyloxy]biphenyl 4-[4'-(2-(R)-octyloxy)-3'-nitrophenyl]benzoate. Both molecules possessed an electron-accepting nitro group placed perpendicular to the long axis of the molecules in order to enhance the nonlinear optical activity. A second generation hydroxyl functional aliphatic dendrimer based on the dihydroxy acid, 2,2-bis(hydroxymethyl)propionic acid, was used as dendritic scaffold and was subsequently functionalized with the aforementioned groups. The purity and structure of the two liquid crystalline dendrimers were determined by H-1 NMR spectroscopy, size exclusion chromatography, and elemental analysis. The synthesis of both the mesogen-containing units and the liquid crystalline dendrimers is described in detail. Investigation of the liquid crystalline properties of the materials by differential scanning calorimetry and optical microscopy showed that they exhibited different mesophases, including the chiral smectic C phase. Ferroelectric switching was observed in this tilted phase, and electrooptical properties, including tilt angle and spontaneous polarization measurements, were investigated. Finally, the nonlinear optical properties of one of the materials were preliminary characterized.
  •  
37.
  • Caggiano, N.J., et al. (författare)
  • Local Chain Alignment via Nematic Ordering Reduces Chain Entanglement in Conjugated Polymers
  • 2018
  • Ingår i: Macromolecules. - : American Chemical Society (ACS). - 1520-5835 .- 0024-9297. ; 51:24, s. 10271-10284
  • Tidskriftsartikel (refereegranskat)abstract
    • Chain entanglements govern the dynamics of polymers and will therefore affect the processability and kinetics of ordering; it follows that through these parameters chain dynamics can also affect charge transport in conjugated polymers. The effect of nematic coupling on chain entanglements is probed by linear viscoelastic measurements on poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) and poly((9,9-dioctylfluorene-2,7-diyl)-alt-(4,7-di(thiophene-2-yl)-2,1,3-benzothiadiazole)-5′,5″-diyl) (PFTBT) with varying molecular weights. We first verify the existence of nematic phases in both PFTBT and PCDTBT and identify nematic-isotropic transition temperatures, TIN, between 260 and 300 °C through a combination of differential scanning calorimetry, polarized optical microscopy, temperature-dependent X-ray scattering, and rheology. In addition, both PCDTBT and PFTBT show a glass transition temperature (Tg) and TIN, whereas only PFTBT has a melting temperature Tm of 260 °C. Comparing the molecular weight dependence of TIN with theoretical predictions of nematic phases in conjugated polymers yields the nematic coupling constant, α = (550 ± 80 K)/T + (2.1 ± 0.1), and the long-chain limit TIN as 350 ± 10 °C for PFTBT. The entanglement molecular weight (Me) in the isotropic phase is extracted to be 11 ± 1 kg/mol for PFTBT and 22 ± 2 kg/mol for PCDTBT by modeling the linear viscoelastic response. Entanglements are significantly reduced through the isotropic-to-nematic transition, leading to a 10-fold increase in Me for PFTBT and a 15-fold increase for PCDTBT in the nematic phase.
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38.
  • Carlmark, Anna, et al. (författare)
  • ATRP of dendronized aliphatic macromonomers of generation one, two, and three
  • 2004
  • Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 37:20, s. 7491-7496
  • Tidskriftsartikel (refereegranskat)abstract
    • Atom transfer radical polymerization (ATRP) of dendritic, aliphatic macromonomers has been investigated. The macromonomers were based on acrylate functionalized 2,2-bis(methylol)propionic acid (bis-MPA) dendrons, with a flexible spacer of 10 carbons incorporated in the structure in between the polymerizable group and the dendritic wedge. Dendronized polymers of generation one, two, and three were successfully synthesized by ATRP. The polymerizations proceeded until over 80% conversion was reached, while maintaining control over polydispersity index (PDI). Plots of ln([M](0)/[M]) vs time for the polymerization of all three macromonomers showed a linear dependence, indicating that the number of propagating radicals in the reaction solution was constant throughout the reaction, when ethyl 2-bromopropionate (EBrP) was used as an initiator (i.e., radical termination was negligible). All of the resulting polymers had low PDI values and molecular weight close to the theoretical ones. The products were analyzed by H-1 and C-13 NMR spectroscopies, size exclusion chromatography (SEC), differential scanning calorimetry (DSC), and matrix-assisted laser desorption-ionization time-of-flight (MALDI-TOF).
  •  
39.
  • Cederholm, Linnea, et al. (författare)
  • Design for Recycling : Polyester- and Polycarbonate-Based A-B-A Block Copolymers and Their Recyclability Back to Monomers
  • 2023
  • Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 56:10, s. 3641-3649
  • Tidskriftsartikel (refereegranskat)abstract
    • Chemical recycling to monomers (CRMs) of A-B-Ablockcopolymers is governed by the chemical structure and thereby the thermodynamicbehavior of different block constituents. Here, we show how a thermodynamictoolkit based on a cyclic monomer structure and solvent propertiescan be utilized in the design of recyclable A-B-A blockcopolymers with varying material properties. By combining four cyclicmonomers lactide, epsilon-decalactone, 2,2-diethyltrimethylene carbonate,and trimethylene carbonate, three different block copolymers werecreated, suitable for different CRM scenarios. The chemical structureof the soft midblock (epsilon-decalactone or trimethylene carbonate)appeared to have a critical impact both on the ring-closing depolymerizationbehavior and mechanical properties, where changing from a polyesterto a polycarbonate soft block increased Young's modulus from14 to 200 MPa. Hence, this work demonstrates the complexity as wellas the opportunities in the design of macromolecular structures fora circular economy.
  •  
40.
  •  
41.
  • Chen, Gaojian, et al. (författare)
  • A modular click approach to glycosylated polymeric beads : Design, synthesis and preliminary lectin, recognition studies
  • 2007
  • Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 40:21, s. 7513-7520
  • Tidskriftsartikel (refereegranskat)abstract
    • Covalent immobilization of a range of carbohydrate derivatives onto polymeric resin beads is described. Copper-catalyzed Huisgen [2 + 3] cycloaddition (often termed click chemistry) was used to graft mannose-containing azides to complementarily functionalized alkyne surfaces, namely (a) Wang resin or (b) Rasta particles consisting of a clickable alkyne polymer loose outer shell and a Wang resin inner core. For the second approach, Wang resin beads were first converted into immobilized living radical polymerization initiators with subsequent polymerization of trimethylsilanyl-protected propargyl methacrylate followed by deprotection with TBAF to yield the desired polyalkyne clickable scaffold. The appropriate (x-mannopyranoside azide was then clicked onto the bead to give a mannose functionalized Rasta resin. IR, gel-phase H-1 NMR, and elemental analysis have been used to characterize the modified resins. The binding abilities of these D-mannose-modified particles were subsequently tested using fluorescein-labeled Concanavalin A (Con A), a lectin that binds certain mannose-containing molecules. Preliminary results indicated that the novel glyco-hybrid materials presented in this work are able to efficiently recognize mannose-binding model lectins such as Con A, opening the way for their potential application in affinity chromatography, sensors, and other protein recognition/separation fields.
  •  
42.
  • Chen, Pan, et al. (författare)
  • Quantifying Localized Macromolecular Dynamics within Hydrated Cellulose Fibril Aggregates
  • 2019
  • Ingår i: Macromolecules. - : AMER CHEMICAL SOC. - 0024-9297 .- 1520-5835. ; 52:19, s. 7278-7288
  • Tidskriftsartikel (refereegranskat)abstract
    • Molecular dynamics (MD) simulations of C-13 NMR longitudinal relaxation (T-1) distributions were recently established as a powerful tool for characterizing moisture adsorption in natural amorphous polymers. Here, such computational-experimental synergy is demonstrated in a system with intrinsically high structural heterogeneity, namely crystalline cellulose nanofibrils (CNFs) in highly hydrated aggregated state. In such a system, structure-function properties on the nanoscale remain largely uncovered by experimental means alone. In this work, broadly polydispersed experimental C-13 NMR T-1 distributions could be successfully reproduced in simulations and, for the first time, were decomposed into contributions from distinct molecular sources within the aggregated CNFs, namely, (i) the core and (ii) the less-accessible and accessible surface regions of the CNFs. Furthermore, within the surface groups structurally different sites such as (iii) residues with different hydroxymethyl orientations and (iv) center and origin chains could be discerned based on their distinct molecular dynamics. The MD simulations unravel a direct correlation between dynamical and structural heterogeneity at an atomistic-level resolution that cannot be accessed by NMR experiments. The proposed approach holds the potential to enable quantitative interpretation of NMR data from a range of multicomponent high-performance nanocomposites with significantly heterogeneous macromolecular structure.
  •  
43.
  • Chen, Yulan, et al. (författare)
  • Facile Synthesis of 3,8-Dibromo-Substituted Phenanthridine Derivatives and Their Conjugated Polymers
  • 2010
  • Ingår i: MACROMOLECULES. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 43:3, s. 1349-1355
  • 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.
  •  
44.
  • Chen, Yongzhen, et al. (författare)
  • In Situ Spectroscopic and Electrical Investigations of Ladder-type Conjugated Polymers Doped with Alkali Metals
  • 2022
  • Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 55:16, s. 7294-7302
  • Tidskriftsartikel (refereegranskat)abstract
    • Ladder-type conjugated polymers exhibit a remarkable performance in (opto)electronic devices. Their double-stranded planar structure promotes an extended pi-conjugation compared to inter-ring-twisted analogues, providing an excellent basis for exploring the effects of charge localization on polaron formation. Here, we investigated alkali-metal n -doping of the ladder-type conjugated polymer (polybenzimidazobenzophe-nanthroline) (BBL) through detailed in situ spectroscopic and electrical characterizations. Photoelectron spectroscopy and ultraviolet-visible-near-infrared (UV-vis-NIR) spectroscopy indicate polaron formation upon potassium (K) doping, which agrees well with theoretical predictions. The semiladder BBB displays a similar evolution in the valence band with the appearance of two new features below the Fermi level upon K-doping. Compared to BBL, distinct differences appear in the UV-vis-NIR spectra due to more localized polaronic states in BBB. The high conductivity (2 S cm(-1)) and low activation energy (44 meV) measured for K-doped BBL suggest disorder-free polaron transport. An even higher conductivity (37 S cm(-1)) is obtained by changing the dopant from K to lithium (Li). We attribute the enhanced conductivity to a decreased perturbation of the polymer nanostructure induced by the smaller Li ions. These results highlight the importance of polymer chain planarity and dopant size for the polaronic state in conjugated polymers.
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45.
  • Cheun, H., et al. (författare)
  • Polarized optical absorption spectroscopy, NEXAFS, and GIXRD measurements of chain alignment in polyfluorene thin films
  • 2008
  • Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 41:17, s. 6463-6472
  • Tidskriftsartikel (refereegranskat)abstract
    • The uniaxial chain alignment of low molecular weight poly(9,9-bis(ethylhexyl)fluorene-2,7-diyl) (PF2/6) in thin films cast atop rubbed polyimide templates is characterized by polarized optical absorption spectroscopy, carbon K near-edge X-ray absorption fine structure spectroscopy (NEXAFS), and grazing incidence X-ray diffraction (GIXRD) in response to thermal annealing and increasing film thickness (ca. 15-150 nm). The highest overall levels of uniaxial alignment are obtained in the thinnest PF2/6 films. However, the orientation of chains at the top surface after thermal annealing is nearly thickness independent despite a large drop in the maximum optical dichroic ratio as the film thickness increases. The kinetics of chain alignment on heating are strongly film thickness dependent and only weakly correlated with a crossover to a nematic liquid crystal state. All told these data support a structural model in which there is a graded morphology such that the top and bottom surfaces exhibit appreciable planar, uniaxial alignment while the film interior includes a greater proportion of nomplanar (i.e., tilted) chains after thermal cycling. These inhomogeneities are likely to influence technologically important optical and transport properties.
  •  
46.
  • Chronakis, IS, et al. (författare)
  • Generation of molecular recognition sites in electrospun polymer nanofibers via molecular imprinting
  • 2006
  • Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 39:1, s. 357-361
  • Tidskriftsartikel (refereegranskat)abstract
    • A simple method for the formation of molecular recognition sites in polymer nanofibers was developed. Electrospun nanofibers were prepared from a Solution mixture of poly(ethylene terephthalate) (PET) and polyallylamine in the presence of a template molecule, 2,4-dichlorophenoxyacetic acid (2,4-D). The polyamine was used to provide functional groups that interact with the template during the electrospinning process, and PET acted as a major supporting matrix to ensure easy fiber formation and to minimize the conformational change of the polymers when the nanofibers were subjected to different solvent treatments. When the template was removed by solvent extraction, imprinted binding sites were left in the nanofiber materials that are capable of selectively rebinding the target molecule. The molecularly imprinted nanofibers were characterized by SEM, FT-IR, and radioligand binding analysis.
  •  
47.
  • Chronakis, IS, et al. (författare)
  • Thermoreversible gels of hydrophobically modified hydroxyethyl cellulose cross-linked by amylose
  • 2002
  • Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 35:10, s. 4113-4122
  • Tidskriftsartikel (refereegranskat)abstract
    • Aqueous mixtures of hydrophobically modified hydroxyethyl cellulose (HMHEC) or unmodified hydroxyethyl cellulose (HEC), with amylose (AM) or potato amylopectin (PAP), have been investigated by rheology, turbidity, and H-1 NMR measurements. It is concluded that the AM molecules cross-link HMHEC chains by forming helical inclusion complexes with the hydrophobic side chains of HMHEC, leading to thermoreversible, elastic, and thixotropic gels at ambient temperatures. The complexation ability, the setting-melting temperature of the AM-HMHEC complexes, the strength of the association, and the viscoelastic behavior of the gels vary with the polymer concentrations, the pH, and the preparation method. AM-HMHEC complexes were obtained at a pH range of 7-12.5, but a maximum storage modulus was observed at pH approximate to 10. The AM-HMHEC complexation is modified or completely abolished by the addition of surfactant. A weak synergistic interaction was found for mixtures of PAP with HNIHEC. No complexation was observed between HEC and either AM or PAP.
  •  
48.
  • Claes, Stan, et al. (författare)
  • Free Volume Expansion of Poly[1-(trimethylsilyl)-1-propyne] Treated in Supercritical Carbon Dioxide As Revealed by Positron Annihilation Lifetime Spectroscopy
  • 2011
  • Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 44:8, s. 2766-2772
  • 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.
  •  
49.
  • Colombini, Didier, et al. (författare)
  • Direct and reverse mechanical modeling of an alkyd acrylic hybrid system: A morphological study
  • 2004
  • Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 37:7, s. 2596-2602
  • Tidskriftsartikel (refereegranskat)abstract
    • Mechanical modeling and dynamic mechanical analysis were associated to investigate the viscoelastic properties of an alkyd acrylic hybrid system in connection with its morphology, which was characterized by transmission electron microscopy. Theoretical predictions based on the interlayer model used in direct mode were successfully combined with the experimental viscoelastic data to lead to relevant additional information about the complex particulate morphology of the hybrid system. Thus, using direct mechanical modeling, it was concluded that the experimental response of the alkyd acrylic hybrid system to a sinusoidal mechanical stress corresponds to the mechanical response of a sample whose morphology involves a acrylic-rich interphase between continuous and dispersed alkyd-rich domains. For the very first time, the interlayer model was then used in reverse mode in order to separate the actual viscoelastic properties of such a acrylic-rich interphase from those experimentally obtained for the alkyd acrylic hybrid system. The differences in these extracted viscoelastic properties, when compared to those of the pure latex film, were presented as reflecting the changes in the molecular mobility of the macromolecules resulting from the mutual influence of the phases in the multiphase hybrid material.
  •  
50.
  • Colombini, Didier, et al. (författare)
  • Influence of the particle size and particle size ratio on the morphology and viscoelastic properties of bimodal hard/soft latex blends
  • 2004
  • Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 37:18, s. 6865-6873
  • Tidskriftsartikel (refereegranskat)abstract
    • The morphology and viscoelastic properties of films prepared from bimodal latex blends containing equal weight fractions of soft and hard latex particles were investigated as a function of the particle sizes and the particle size ratio (soft particle diameter/hard particle diameter). Minimum film formation temperature (MFT) measurements were associated with transmission electron microscopy (TEM) to emphasize the particle size ratio dependence of the film formation properties. A significant increase of the MFT values with the soft/hard particle size ratio was observed. As long as the particle size ratio was low, TEM micrographs showed that the film forming soft particles, undergoing complete coalescence, clearly act as the continuous phase where the non film forming hard particles are found evenly dispersed while keeping their initial spherical shape. At higher values of the particle size ratio, TEM micrographs pointed out that the soft particles are prevented from coming into contact with each other by the surrounding hard particles, therefore dramatically increasing the MFT of the sample and resulting in a non film forming latex blend. The existence of a critical volume fraction of hard particles that is directly related to the soft/hard particle size ratio was then established on the basis of geometrical arguments involving the percolation theory. The higher the particle size ratio, the lower the critical volume fraction of hard particles that leads to a macroscopic phase inversion resulting in a non film forming bimodal latex blend. Subsequently, the mechanical film properties were investigated by solid-state dynamic mechanical analysis. The size of the dispersed hard phase was found to affect the final viscoelastic film properties. The smaller the size of the hard particles, the better the mechanical enhancement of the mechanical film properties. Last, the experimental viscoelastic thermograms were compared with some theoretical predictions based on self-consistent mechanical modeling. The final film properties of the bimodal hard/soft latex blends were then directly connected to the film formation properties.
  •  
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