Showing papers in "Macromolecules in 2005"
TL;DR: In this paper, a new and highly efficient direct solvent, 1-allyl-3methylimidazolium chloride (AMIMCl), has been used for the dissolution and regeneration of cellulose.
Abstract: A new and highly efficient direct solvent, 1-allyl-3-methylimidazolium chloride (AMIMCl), has been used for the dissolution and regeneration of cellulose. The cellulose samples without any pretreatment were readily dissolved in AMIMCl. The regenerated cellulose materials prepared by coagulation in water exhibited a good mechanical property. Because of its thermostable and nonvolatile nature, AMIMCl was easily recycled. Therefore, a novel and nonpolluting process for the manufacture of regenerated cellulose materials using AMIMCl has been developed in this work.
1,307 citations
TL;DR: In this article, the authors showed that in-plane π-stacking does not cause the mobility−MW relationship, and that modifying the morphology for a constant number-average molecular weight (MW) by changing the casting conditions or annealing the samples strongly affects the charge transport and morphology in the low-mobility, low-MW films, but has little effect on the high-mogulular poly(3-hexylthiophene).
Abstract: Morphological characterization has been used to explain the previously observed strong correlation between charge carrier mobility measured with thin-film transistors and the number-average molecular weight (MW) of the conjugated polymer regioregular poly(3-hexylthiophene). Atomic force microscopy and X-ray diffraction show that the low-mobility, low-MW films have a highly ordered structure composed of nanorods and the high-mobility, high-MW films have a less ordered, isotropic nodule structure. Modifying the morphology for a constant MW by changing the casting conditions or annealing the samples strongly affects the charge transport and morphology in the low-mobility, low-MW films, but has little effect on the high-MW films. In-plane grazing incidence X-ray scattering shows the in-plane π-stacking peak increases when the mobility increases for a constant MW. When the MW is changed, this correlation breaks down, confirming that in-plane π-stacking does not cause the mobility−MW relationship. We believe a ...
1,020 citations
TL;DR: In this paper, a new crystal modification named the α form was proposed for the crystal structure of poly(l-lactic acid) samples annealed at temperature below 120 °C.
Abstract: Recently, we reported the isothermal crystallization behaviors of poly(l-lactic acid) (PLLA) from the melt and glassy states, respectively [J. Phys. Chem. B 2004, 108, 11514; Macromolecules 2004, 37, 6433]. Surprisingly, the quite different infrared (IR) spectral evolutions occur in the two crystallization processes at different temperatures in which the same crystal modification is expected to be formed. To clarify this unusual phenomenon, the crystal modifications and thermal behavior of PLLA samples prepared under different crystallization temperatures are investigated in detail by TEM, WAXD, and FTIR techniques. On the basis of the WAXD and IR data, a new crystal modification named the α form is proposed for the crystal structure of PLLA samples annealed at temperature below 120 °C. Such crystal modification with loose 103 helical chain packing is less thermally stable than the standard α form of PLLA. This assignment can explain all the experiment observations well. Other possible mechanisms for the ...
751 citations
TL;DR: In this paper, the effects of charge density on weak polyelectrolyte multilayer growth were investigated by assembling several strong poly electrolytes with either poly(allylamine hydrochloride) (PAH) or poly(acrylic acid) (PAA) to keep one polymer fully charged while varying the degree of ionization of the other.
Abstract: The effects of charge density on weak polyelectrolyte multilayer growth were investigated by assembling several strong polyelectrolytes with either poly(allylamine hydrochloride) (PAH) or poly(acrylic acid) (PAA) to keep one polymer fully charged while varying the degree of ionization of the other. The degree of ionization of the weak polyelectrolytes in solution and in a multilayer film was controlled by pH adjustment and quantified by Fourier transform infrared spectroscopy analyses. In all cases, the bilayer thickness exhibited a dramatic change from molecularly thin bilayers (case of two fully charged polymers) to much thicker bilayers when the degree of ionization of the weak polyelectrolyte decreased below 70−90% charged units. We also confirmed and quantified earlier observations that both the charge density and the effective pKa of a weak polyelectrolyte can change substantially from solution-state values when the polymer is incorporated into a multilayer film. In addition, it was found that the d...
734 citations
TL;DR: In this paper, a versatile method to produce superhydrophobic surfaces by combining electrospinning and initiated chemical vapor deposition (iCVD) is described, and a wide variety of surfaces including electrospun polyester fibers, may be coated by the inventive method.
Abstract: Disclosed is a versatile method to produce superhydrophobic surfaces by combining electrospinning and initiated chemical vapor deposition (iCVD). A wide variety of surfaces, including electrospun polyester fibers, may be coated by the inventive method. In one embodiment, poly(caprolactone) (PCL) was electrospun and then coated by iCVD with a thin layer of hydrophobic polymerized perfluoroalkyl ethyl methacrylate (PPFEMA). In certain embodiments said coated surfaces exhibit water contact angles of above 150 degrees, oleophobicities of at least Grade-8 and sliding angles of less than 12 degrees (for a water droplet of about 20 mg).
641 citations
TL;DR: The Grignard metathesis (GRIM) polymerization of 3-alkylthiophenes proceeds by a quasi-living chain growth mechanism, not by a step growth process as mentioned in this paper.
Abstract: The Grignard metathesis (GRIM) polymerization of 3-alkylthiophenes proceeds by a quasi-“living” chain growth mechanism, not by a step growth process. Kinetic studies of the Grignard metathesis polymerization of 2,5-dibromo-3-alkylthiophenes showed that the molecular weight of poly(3-alkylthiophenes) is a function of the molar ratio of the monomer to nickel initiator, and conducting polymers with predetermined molecular weights and relatively narrow molecular weight distributions (PDIs = 1.2−1.5) can be made. Sequential monomer addition resulted in new block copolymers containing different poly(3-alkylthiophene) segments.
602 citations
TL;DR: In this article, a method is developed to enable emulsion polymerization to be performed under RAFT control to give living character without the problems that often affect such systems: formation of an oily layer, loss of colloidal stability, or loss of molecular weight control.
Abstract: A method is developed to enable emulsion polymerization to be performed under RAFT control to give living character without the problems that often affect such systems: formation of an oily layer, loss of colloidal stability, or loss of molecular weight control. Trithiocarbonate RAFT agents are used to form short stabilizing blocks from a water-soluble monomer, from which diblocks can be created by the subsequent polymerization of a hydrophobic monomer. These diblocks are designed to self-assemble to form micelles. Polymerization is initially performed under conditions that avoid the presence of monomer droplets during the particle formation stage and until the hydrophobic ends of the diblocks have become sufficiently long to prevent them from desorbing from the newly formed particles. Polymerization is then continued at any desired feed rate and composition of monomer. The polymer forming in the reaction remains under RAFT control throughout the polymerization; molecular weight polydispersities are generally low. The number of RAFT-ended chains within a particle is much larger than the aggregation number at which the original micelles would have self-assembled, implying that in the early stages of the polymerization, there is aggregation of the micelles and/or migration of the diblocks. The latexes resulting from this approach are stabilized by anchored blocks of the hydrophilic monomer, e.g., acrylic acid, with no labile surfactant present. Sequential polymerization of two hydrophobic monomers gives completely novel core-shell particles where most chains extend from the core of the particles through the shell layer to the surface.
566 citations
TL;DR: In this article, the microstructures of the nanocomposites (epoxy/S-clays) were characterized by means of optical microscopy and transmission electron microscopy (TEM).
Abstract: Epoxy/clay nanocomposites with a better exfoliated morphology have been successfully prepared using a so-called “slurry-compounding” process. The microstructures of the nanocomposites (epoxy/S-clays) were characterized by means of optical microscopy and transmission electron microscopy (TEM). It was found that clay was highly exfoliated and uniformly dispersed in the resulting nanocomposite. Characterizations of mechanical and fracture behaviors revealed that Young's modulus increases monotonically with increasing the clay concentration while the fracture toughness shows a maximum at 2.5 wt % of clay. No R-curve behavior was observed in these nanocomposites. The microdeformation and fracture mechanisms were investigated by studying the microstructure of arrested crack tips and the damage zone using TEM and scanning electron microscopy (SEM). The initiation and development of microcracks are the dominant microdeformation and fracture mechanisms in the epoxy/S-clay nanocomposites. Most of the microcracks in...
533 citations
TL;DR: In this paper, a novel procedure was developed for activation of an oxidatively stable catalyst complex added to an atom transfer radical polymerization (ATRP) procedure, which improved the simultaneous normal and reverse initiation (SR&NI) by eliminating free radical initiators for the activation of the higher oxidation state catalyst complex.
Abstract: A novel procedure was developed for activation of an oxidatively stable catalyst complex added to an atom transfer radical polymerization (ATRP). Tin(II) 2-ethylhexanoate (Sn(EH)2) was used as a reducing agent of various Cu(II) complexes in ATRP of various monomers initiated by alkyl halides. This approach further improves a simultaneous normal and reverse initiation (SR&NI) by eliminating free radical initiators for the activation of the higher oxidation state catalyst complex. As a result, “activator generated by electron transfer” (AGET) ATRP allows the preparation of pure block copolymers. Several combinations of monomer/catalyst complex precursor were studied, including styrene/CuCl2/dNbpy, octadecyl methacrylate/CuCl2/dNbipy, methyl methacrylate/CuCl2/PMDETA, n-butyl acrylate/CuBr2/PMDETA, and methyl acrylate/CuCl2/Me6TREN. Polymerization proceeded in a controlled way for all systems, producing well-defined polymers with controlled degree of polymerization and narrow molecular weight distribution, d...
528 citations
TL;DR: In this paper, a surface-initiated ATRP of methyl methacrylate mediated by a copper complex was carried out with the initiator-fixed SiPs in the presence of a free initiator.
Abstract: Monodisperse silica particles (SiPs) of diameter between 100 and 1500 nm were surface-modified in a mixture of ethanol/water/ammonia with a newly designed triethoxysilane having an atom transfer radical polymerization (ATRP) initiating site, (2-bromo-2-methyl)propionyloxyhexyltriethoxysilane. The surface-initiated ATRP of methyl methacrylate (MMA) mediated by a copper complex was carried out with the initiator-fixed SiPs in the presence of a “sacrificial” (free) initiator. The polymerization proceeded in a living manner in all examined cases, producing SiPs coated with well-defined PMMA of a target molecular weight up to 480K with a graft density as high as 0.65 chains/nm2. These hybrid particles had an exceptionally good dispersibility in organic solvents. Transmission electron microscopic and atomic force microscopic observations of their monolayers prepared at the air−water interface revealed that they formed an ordered 2-dimensional lattice extending throughout the monolayer.
527 citations
TL;DR: In this paper, room temperature atom transfer radical polymerization of N-isopropylacrylamide (NIPAM) carried out in 2-propanol (i-PrOH) and tert-butyl alcohol (t-BuOH) resulted in PnIPAMs with polydispersities.
Abstract: Room temperature atom transfer radical polymerizations of N-isopropylacrylamide (NIPAM) carried out in 2-propanol (i-PrOH) and tert-butyl alcohol (t-BuOH) resulted in PNIPAMs with polydispersities ...
TL;DR: In this article, the process of forming the unique organic/inorganic network structure of nanocomposite hydrogels (NC gels) was studied through changes in viscosity, optical transparency, X-ray diffraction, and mechanical properties.
Abstract: The process of forming the unique organic/inorganic network structure of nanocomposite hydrogels (NC gels) was studied through changes in viscosity, optical transparency, X-ray diffraction, and mechanical properties. It was concluded that, during the preparation of the initial reaction solutions, a specific solution structure was formed from monomer (NIPA) and clay, where NIPA prevents gel formation of clay itself, and initiator (KPS) is located near the clay surface through ionic interactions. In subsequent in-situ free-radical polymerization, it was observed that the viscosity increased markedly during NC gel syntheses and in a manner similar to that in OR gel syntheses. Also, NC gels with different polymer contents exhibit characteristic two-step changes in the stress−strain curves, which correspond to the primary network formation and subsequent increase of cross-link density. These are because the polymerization proceeds on the clay particles which are relatively immobile, and clay platelets act as e...
TL;DR: In this article, the Atom Transfer Radical Polymerization (ATRP) of propargyl methacrylate (PgMA) resulted in high polydispersities (Mw/Mn > 3), multimodal molecular weight distributions, and cross-linked networks at moderate to high conversion.
Abstract: To prepare polymers with pendant functionality capable of participating in highly efficient CuI-catalyzed 1,3-dipolar cycloaddition of azide and alkynes, monomers with acetylene or azido groups were polymerized via controlled radical polymerization Atom transfer radical polymerization (ATRP) of propargyl methacrylate (PgMA) resulted in high polydispersities (Mw/Mn > 3), multimodal molecular weight distributions, and cross-linked networks at moderate to high conversion The poor results obtained with this monomer were presumably due to addition of the propagating radicals to the acetylene group, transfer reactions, and/or interference with the catalyst A novel monomer, 3-azidopropyl methacrylate (AzPMA), was polymerized via ATRP with good control of the polymer molecular weight distribution and retention of chain functionality Poly(3-azidopropyl methacrylate) was coupled with propargyl alcohol, propargyl triphenylphosphonium bromide, propargyl 2-bromoisobutyrate, and 4-pentynoic acid via a highly effici
TL;DR: In this paper, structural and conformational properties of generations 4, 5, and 6 PAMAM dendrimers at various protonation levels through extensive molecular dynamics simulations in explicit solvent were reported.
Abstract: We report various structural and conformational properties of generations 4, 5, and 6 PAMAM (polyamidoamine) dendrimer [EDA (ethylenediamine) core)] at various protonation levels through extensive molecular dynamics (MD) simulations in explicit solvent. The presence of solvent leads to swelling of the dendrimer (by 33% for G5 compared to the case of no solvent). We find that decreasing the solution from high pH (∼10, no protonation) to neutral (∼7, only primary amines protonated) to low pH (∼4, tertiary amines also protonated) changes the radius of gyration of G5 from 21 to 22 to 25 A, respectively. We also report such other structural quantities as radial density, distribution of terminal groups, solvent accessible surface area and volume, shape, and structure factors (to compare with SAXS and SANS experiments) at various pH conditions. We find significant back-folding of the outer subgenerations in the interior of the molecules at all levels of pH, contrary to original expectations and some SANS experiments but in agreement with other SANS experiments. We find significant water penetration inside the dendrimer, with ∼3 water/tertiary amine for high pH and ∼6 water/tertiary amine for low pH (all for G5). This indicates that the interior of the dendrimer is quite open with internal cavities available for accommodating guest molecules, suggesting using PAMAM dendrimer for guest−host applications. This estimate of internal waters suggests that sufficient water is available to facilitate metal ion binding.
Abstract: A novel series of semiconducting conjugated copolymers, derived from alkyl-substituted fluorene, 4,7-diselenophen-2‘-yl-2,1,3-benzothiadiazole (SeBT), and 4,7-diselenophen-2‘-yl-2,1,3-benzoselenadiazole (SeBSe), was synthesized by a palladium-catalyzed Suzuki coupling reaction with various feed ratios. The optical band gap of copolymers is very low, 1.87 eV for SeBT and 1.77 eV for SeBSe. The efficient fast energy transfer from fluorene segments to narrow-band-gap sites was observed. The emission of photoluminescence and electroluminescence is dominated by narrow-band-gap species and peaked at 670−790 nm, in the range from deep-red to near-infrared (NIR). The external electroluminescent (EL) quantum efficiencies reached 1.1% and 0.3% for devices from these two types of copolymers, respectively. Bulk−heterojunction polymer photovoltaic cells (PPVCs) made from composite thin film of the copolymer 9,9-dioctylfluorene and SeBT (PFO−SeBT) in blend with fullerene derivative [6,6]-phenyl C61 butyric acid methyl ...
TL;DR: The high fidelity and efficiency of Click chemistry are exploited in the synthesis of a library of chain end functionalized dendritic macromolecules, demonstrating an evolving synergy between advanced organic chemistry and functional materials.
Abstract: The high fidelity and efficiency of Click chemistry are exploited in the synthesis of a library of chain end functionalized dendritic macromolecules. In this example, the selectivity of the Cu-catalyzed [3 + 2π] cycloaddition reaction of azides with terminal acetylenes, coupled with mild reaction conditions, permits unprecedented functional group tolerance during the derivatization of dendrimeric and hyperbranched scaffolds. The resulting dendritic libraries are structurally diverse, encompassing a variety of backbones/surface functional groups, and are prepared in almost quantitative yields under very mild conditions. The robust and simple nature of this procedure, combined with its applicability to many aspects of polymer synthesis and materials chemistry, demonstrates an evolving synergy between advanced organic chemistry and functional materials.
TL;DR: In this article, phase diagrams with very flat LCST phase separation line for aqueous poly(N-isopropylacrylamide) (PNIPAM) solutions are theoretically derived on the basis of sequential hydrogen bond formation between polymer chains and water molecules (cooperative hydration) and compared with experimental spinodal curves.
Abstract: Phase diagrams with very flat LCST phase separation line for aqueous poly(N-isopropylacrylamide) (PNIPAM) solutions are theoretically derived on the basis of sequential hydrogen bond formation between polymer chains and water molecules (cooperative hydration) and compared with experimental spinodal curves. The two-phase region systematically changes its shape with the cooperativity parameter σ, and the spinodals turned out to be almost independent of the polymer molecular weight for strongly cooperative hydration (small σ) as observed in PNIPAM solutions. Hydration takes place sharply within a very narrow temperature region. The number of hydrogen-bonded water molecules on a chain is calculated as a function of the temperature and the polymer concentration.
TL;DR: In this paper, surface carboxylated cellulose nanocrystals with different sizes and degrees of oxidation were prepared by TEMPO-mediated oxidation of cotton linters and microfibrils of parenchyma cell cellulose (PCC).
Abstract: Surface carboxylated cellulose nanocrystals with different sizes and degrees of oxidation were prepared by TEMPO-mediated oxidation of cotton linters and microfibrils of parenchyma cell cellulose (PCC). The size of the oxidized crystals depended on (i) the starting material, (ii) an eventual acid prehydrolysis, and (iii) the oxidation conditions. The oxidized cellulose nanocrystals were characterized by transmission electron microscopy, conductometric titration, and solid-state NMR spectroscopy. During TEMPO oxidation, the main reaction corresponded to a selective oxidation of surface primary hydroxyl groups into carboxylic groups. At the same time, a decrease of the crystal size occurred, resulting from some degradation in the amorphous areas of the starting material. The introduction of negative charges at the interface of the crystalline domains induced a better individualization of the crystallites. The degrees of oxidation (DO) determined by conductometric titration were in agreement with those deduc...
TL;DR: In this article, the authors derived a GISAXS formula under the distorted wave Born approximation for various compositions of polystyrene-b-polyisoprene (PS-bPI) diblock copolymer thin films on silicon substrates.
Abstract: The grazing incidence small-angle X-ray scattering (GISAXS) from structures within a thin film on a substrate is generally a superposition of the two scatterings generated by the two X-ray beams (reflected and transmitted beams) converging on the film with a difference of twice the incidence angle (αi) of the X-ray beam in their angular directions; these two scatterings may overlap or may be distinct, depending on αi. The two scatterings are further distorted by the effects of refraction. These reflection and refraction effects mean that GISAXS is complicated to analyze. To quantitatively analyze GISAXS patterns, in this study we derived a GISAXS formula under the distorted wave Born approximation. We applied this formula to the quantitative analysis of the GISAXS patterns obtained for various compositions of polystyrene-b-polyisoprene (PS-b-PI) diblock copolymer thin films on silicon substrates with native oxide layers. This analysis showed that the diblock copolymer thin films consist of hexagonally pac...
TL;DR: Using a modified Grignard metathesis (GRIM) reaction, a series of polymers have been synthesized bearing functional groups on one or both ends of the polymer as mentioned in this paper.
Abstract: A simple method for the synthesis of end-functionalized regioregular poly(3-alkylthiophene)s is presented. Using a modified Grignard metathesis (GRIM) reaction, a series of polymers have been synthesized bearing functional groups on one or both ends of the polymer. This method has been demonstrated to work with a variety of different types of Grignard reagents (i.e., aryl, alkyl, allyl, vinyl, etc.). The reactivity of these depends on their nature, where allyl, ethynyl, and vinyl groups produced monofunctionalized polymers, and all others yielded difunctionalized polymers. The end group composition of the polymers was monitored by a combination of MALDI-TOF and 1H NMR and approaches 100% in most cases. By utilizing the proper protecting groups −OH, −CHO, and −NH2 groups have been incorporated onto the polymer ends. The main advantage of this method is that it allows for the in situ functionalization of regioregular polythiophene, generating a variety of end-capped polymers in one step. This approach is ad...
TL;DR: In this article, reversible addition-fragmentation chain transfer polymerization (RAFT) was used to prepare polymer brushes grafted onto silica nanoparticles, and the results showed that the molecular weights of grafted polymers increased linearly with conversions, and first-order kinetics were observed in the conversion range studied.
Abstract: Reversible addition−fragmentation chain transfer polymerization (RAFT) was used to prepare polymer brushes grafted onto silica nanoparticles. Novel RAFT-silane agents were prepared that contained both an active RAFT moiety and a silane coupling agent. RAFT agents were anchored to silica nanoparticles by the functionalization of colloidal silica with the RAFT-silane agents. RAFT polymerizations were then conducted from the particle surface to graft homopolymer and block copolymer brushes to the particles. The kinetics of styrene (St) and n-butyl acrylate (nBuA) surface RAFT polymerizations were investigated and compared with model polymerizations mediated by free RAFT agent. The molecular weights of grafted polymers increased linearly with conversions, and first-order kinetics were observed in the conversion range studied, indicating that the surface graft polymerization proceeded in a controlled manner. Well-defined PSt-block-PBuA copolymers attached to silica nanoparticles were also prepared.
TL;DR: In this paper, the effects of side chain length on the molecular aggregation states and surface properties of poly(fluoroalkyl acrylate) [PFA-Cy, where y is the fluoromethylene number of the Rf groups] thin films were systematically investigated.
Abstract: The effects of side chain length on the molecular aggregation states and surface properties of poly(fluoroalkyl acrylate) [PFA-Cy, where y is the fluoromethylene number of the Rf groups] thin films were systematically investigated. Spin-coated PFA-Cy thin films were characterized by static and dynamic contact angle measurements, X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry, and wide-angle X-ray diffraction. The receding contact angles showed small values for PFA-Cy with short side chain (y ≤ 6) and increased for ones with y ≥ 8. It has been revealed that PFA-Cy with y ≥ 8 was crystallized and formed ordered structures. These results suggest that the water-repellent mechanism of PFA-Cy can be attributed to the presence of highly ordered fluoroalkyl chains at the outermost surfaces. The results of XPS in the dried and hydrated states and the contact angle measurement in water indicate that the contact angle for water is lowered by exposure of the carbonyl groups to the water int...
TL;DR: In this paper, the authors used real-time infrared spectroscopy during the isothermal melt crystallization process of the PLLA/PDLA stereocomplex and observed a very small low-frequency shift (about 1 cm-1) of νas(CH3) and a much larger low-fractional shift (approximately 5 cm -1) for ν(CO) of poly(l-lactide) chains.
Abstract: The nature of the “peculiarly strong” interaction between the poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) chains was investigated by real time infrared spectroscopy during the isothermal melt crystallization process of the PLLA/PDLA stereocomplex. A very small low-frequency shift (about 1 cm-1) of νas(CH3) and a larger low-frequency shift (about 5 cm-1) of ν(CO) were observed. The typical butterfly pattern in the two-dimensional (2D) asynchronous correlation spectrum and the second-derivative spectra reveal that there is a “peak shift” for ν(CO). The red shifts of the stretching vibration modes of the methyl and carbonyl groups suggest that the interaction between the PLLA/PDLA stereocomplex is ascribed to CH3···OC hydrogen bonding. Another interesting result is that the peak shift of the ν(CO) band already occurs in the induction period, which indicates that the CH3···OC interaction is the driving force for forming the racemic nucleation of the PLLA/PDLA stereocomplex. Moreover, the 2D correlation ...
TL;DR: A series of poly(phenylene)-based polyelectrolytes were synthesized from 1,4-bis(2,4,5-triphenylcyclopentadienone)benzene and 1, 4-diethynyl benzene by Diels−Alder polymerization.
Abstract: A series of poly(phenylene)-based polyelectrolytes were synthesized from 1,4-bis(2,4,5-triphenylcyclopentadienone)benzene and 1,4-diethynylbenzene by Diels−Alder polymerization. Postsulfonation of this high molecular weight and thermochemically stable poly(phenylene) with chlorosulfonic acid resulted in homogeneous polyelectrolytes with controllable ion content (IEC = 0.98−2.2 mequiv/g). Fuel cell relevant properties such as high proton conductivity (123 mS/cm), chemical/thermal stability, and film toughness suggest that this polyelectrolyte material shows promise as a potential candidate for polymer electrolyte membrane fuel cells. Physical properties of this material, such as water uptake, thermal stability, and proton conductivity, are reported with respect to ion exchange capacity and compared to Nafion and a series of sulfonated poly(ether sulfone)s.
TL;DR: In this paper, the effect of nanoconfinement on the glass transition temperature (Tg) of supported polystyrene (PS) films is investigated over a broad molecular weight (MW) range of 5000−3'000'000 g/mol.
Abstract: The effect of nanoconfinement on the glass transition temperature (Tg) of supported polystyrene (PS) films is investigated over a broad molecular weight (MW) range of 5000−3 000 000 g/mol. Polystyrene MW is shown to have no significant impact on the film thickness dependence of Tg − Tg,bulk. In contrast, a small modification to the repeat unit structure of PS has a dramatic impact on the Tg-nanoconfinement effect. The strength of the thickness dependence of Tg is greater for poly(4-methylstyrene) (P4MS) than for PS and yet much greater for poly(4-tert-butylstyrene) (PTBS). The Tg reduction for PTBS is 47 K below Tg,bulk for a 25 nm thick film, with the onset thickness for confinement effects in PTBS being 300−400 nm. Measurements of the size of cooperatively rearranging regions, ξCRR, in bulk polymer systems at Tg reveal that PS MW has no significant effect on ξCRR unless PS is oligomeric or nearly oligomeric. However, changes to repeat unit structure and diluent addition affect ξCRR values, but not in a ...
TL;DR: In this article, a new series of poly(p-phenylenebutadiynylene)s has been synthesized with unique polymer structural features, and the fluorescence quenching properties of these polymers in response to a series of electron-deficient aromatic compounds have been investigated in both solution and the solid state.
Abstract: A new series of poly(p-phenylenebutadiynylene)s has been synthesized with unique polymer structural features. In these systems each of the p-phenylene units in the conjugated backbone is the core of a rigid three-dimensional iptycene scaffold. The fluorescence quenching properties of these polymers in response to a series of electron-deficient aromatic compounds have been investigated in both solution and the solid state. It was found that in solution these polymers displayed higher quenching sensitivity toward studied quenchers compared to a more open-structure iptycene-containing poly(p-phenyleneethynylene). The quenching behaviors of the conjugated polymer were shown to be strongly influenced by the configuration of the incorporated iptycences. The thin films investigations revealed differences in both the fluorescence quenching and the recovery processes. Distinct behaviors indicated that the fluorescence quenching in the solid state is dictated by different factors than those in solution. Our results...
TL;DR: In this article, a series of cross-linked polymers, XLPEGDA, was prepared by photopolymerizing poly(ethylene glycol) diacrylate in the presence of varying amounts of water or monofunctional poly(methylene gl...
Abstract: A series of cross-linked polymers, XLPEGDA, was prepared by photopolymerizing poly(ethylene glycol) diacrylate (PEGDA) in the presence of varying amounts of water or monofunctional poly(ethylene gl...