Showing papers in "Journal of Polymer Science Part A in 2003"
TL;DR: In this article, the reaction mechanism of chitosan, bovine serum albumin (BSA), and gelatin with genipin (a natural crosslinking reagent) was examined with infrared, ultraviolet-visible, and 13C NMR spectroscopies; protein-transfer reaction mass spectrometry; photon correlation spectroscopy; and dynamic oscillatory rheometry.
Abstract: The reaction mechanism of chitosan, bovine serum albumin (BSA), and gelatin with genipin (a natural crosslinking reagent) was examined with infrared, ultraviolet–visible, and 13C NMR spectroscopies; protein-transfer reaction mass spectrometry; photon correlation spectroscopy; and dynamic oscillatory rheometry. Two reactions that proceeded at different rates led to the formation of crosslinks between primary amine groups. The fastest reaction to occur was a nucleophilic attack on genipin by a primary amine group that led to the formation of a heterocyclic compound of genipin linked to the glucosamine residue in chitosan and the basic residues in BSA and gelatin. The second, slower, reaction was the nucleophilic substitution of the ester group possessed by genipin to form a secondary amide link with chitosan, BSA, or gelatin. A decreased crosslinking rate in the presence of deuterium oxide rather than water suggested that acid catalysis was necessary for one or both of the reactions to proceed. The behavior of the gel time with polymer concentration was consistent with second-order gelation kinetics resulting from an irreversible crosslinking process, but was complicated by the oxygen radical-induced polymerization of genipin that caused the gels to assume a blue color in the presence of air. The lower elastic modulus attained after a given time during crosslinking of the globular protein BSA as compared to the coiled protein gelatin, despite possessing more crosslinkable basic residues, demonstrated the importance of protein secondary and tertiary structures in determining the availability of sites for crosslinking with genipin in protein systems. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3941–3953, 2003
541 citations
TL;DR: In this paper, the authors describe recent developments in reversible addition-fragmentation transfer (RAFT) polymerization and provide details of synthetic methodologies for making a wide range of architectures ranging from stars to combs, microgels, and blocks.
Abstract: This highlight describes recent developments in reversible addition-fragmentation transfer (RAFT) polymerization. Succinct coverage of the RAFT mechanism is supplemented by details of synthetic methodologies for making a wide range of architectures ranging from stars to combs, microgels, and blocks. In addition, RAFT reactions in different media such as emulsion and ionic liquids receive attention. Finally, a specific example of a novel material design is briefly introduced, whereas polymers prepared via RAFT are adopted for microporous/honeycomb membrane design.
367 citations
TL;DR: In this article, the authors focus on applications of dendrimers that take advantage of their structural features and polyva- lent character, which can be applied to the design of a varied array of energy harvesting, light- emitting, or catalytic macromole- cules.
Abstract: Given their size, in the single-digit nanometer range, and the versatility of their function- ality, dendrimers and other dendritic macromolecules are poised to make a significant contribution to the rap- idly expanding fields of nanoscience and nanotechnology. This highlight focuses on nascent applications of dendrimers that take advantage of their structural features and polyva- lent character. In particular, the con- cept of dendritic encapsulation of function, borrowed from Nature, can be applied to the design of a varied array of energy-harvesting, light- emitting, or catalytic macromole- cules. Similarly, the compact size and hierarchical ordering of compo- nents within dendrimers make them ideal for exploring the limits of nanolithography. Finally, the pres- ence of differentiated functionalities and the polyvalent character of den-
335 citations
TL;DR: In this article, the internal structures of polyamide-6 and polylactide nanofibers with an average diameter of about 50 nm were analyzed, and they were found to be partially crystalline, with degrees of crystallinity not significantly smaller than those found for less rapidly quenched and much thicker melt-extruded fibers.
Abstract: Electrospinning gives rise to polymer nanofibers. The spinning process is characterized by strong deformations of the polymer material taking place during the spinning process and a very rapid structure formation process happening within milliseconds. We were interested in the influence of the peculiar spinning process on the structures of nanofibers. For this purpose, we analyzed the internal structures of nanofibers spun from polyamide-6 and polylactide with an average diameter of about 50 nm. The fibers were partially crystalline, with degrees of crystallinity not significantly smaller than those found for less rapidly quenched and much thicker melt-extruded fibers. The annealing of polyamide fibers at elevated temperatures resulted in a transformation from the disordered γ modification to the more highly ordered α modification, and this again was in close agreement with the response of melt-extruded fibers. The orientation of the crystals along the fiber axis was strongly inhomogeneous: it was, on average, very weak, yet it could be quite pronounced locally. Small elongations of approximately 10% resulted in well-developed homogeneous crystal orientations. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 545–553, 2003
332 citations
TL;DR: In this article, sulfonated poly(arylene ether sulfone) copolymers with high molecular weights were successfully synthesized with controlled degrees of disulfonation of up to 70 mol % via the direct copolymerization of sulfonsated aromatic dihalides and one of four structurally distinct bisphenols.
Abstract: New sulfonated poly(arylene ether sulfone) copolymers with high molecular weights were successfully synthesized with controlled degrees of disulfonation of up to 70 mol % via the direct copolymerization of sulfonated aromatic dihalides, aromatic dihalides, and one of four structurally distinct bisphenols. The disodium salts of the 3,3′-disulfonated-4,4′-dichlorodiphenyl sulfone and 3,3′-disulfonated-4,4′-difluorodiphenyl sulfone comonomers were synthesized via the sulfonation of 4,4′-dichlorodiphenyl sulfone or 4,4′-difluorodiphenyl sulfone with 30% fuming sulfuric acid at 110 °C. Four bisphenols (4,4′-bisphenol A, 4,4′-bisphenol AF, 4,4′-biphenol, and hydroquinone) were investigated for the syntheses of novel copolymers with controlled degrees of sulfonation. The composition and incorporation of the sulfonated repeat unit into the copolymers were confirmed by 1H NMR and Fourier transform infrared spectroscopy. Solubility tests on the sulfonated copolymers confirmed that no crosslinking and probably no branching occurred during the copolymerizations. Tough, ductile films were solvent-cast that exhibited increased water absorption with increasing degrees of sulfonation. These copolymers are promising candidates for high temperature proton-exchange membranes in fuel cells, which will be reported separately in part II of this series. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2264–2276, 2003
276 citations
TL;DR: In this paper, a rigid polyacetylene skeleton is used to guide the alignments of mesogenic pendants and proves that polyacetylenes can be highly emissive with photoluminescence quantum yields of up to 98% and electrolumine performances comparable or superior to those of the best blue-light-emitting polymers.
Abstract: Rigid polymer backbones have often been considered to be detrimental to the packing of mesogenic pendants, and polyacetylenes have generally been regarded as unpromising materials for light-emitting applications. Our group, however, has succeeded in creating a series of liquid-crystalline polyacetylenes with rigid backbones and a variety of light-emitting polyacetylenes with luminescent chromophores. Here we demonstrate that the rigid polyacetylene skeleton can play a constructive role in guiding the alignments of mesogenic pendants and prove that polyacetylenes can be highly emissive with photoluminescence quantum yields of up to 98% and electroluminescence performances comparable or superior to those of the best blue-light-emitting polymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2607–2629, 2003
217 citations
TL;DR: In this paper, the first living radical polymerization of vinyl chloride carried out in water at 25 °C was reported, initiated by iodoform and catalyzed by nascent Cu0 produced by the disproportionation of CuI in the presence of strongly CuII binding ligands such as tris(2-aminoethyl)amine or polyethyleneimine.
Abstract: The first example of living radical polymerization of vinyl chloride carried out in water at 25 °C is reported. This polymerization was initiated by iodoform and catalyzed by nascent Cu0 produced by the disproportionation of CuI in the presence of strongly CuII binding ligands such as tris(2-aminoethyl)amine or polyethyleneimine. The resulting poly(vinyl chloride) was free of structural defects, had controlled molecular weight and narrow molecular weight distribution, contained two ∼CHClI active chain ends, and had a higher syndiotacticity (62%) than the one obtained by conventional free-radical polymerization at the same temperature (56%). This novel polymerization proceeds, most probably, by a combination of competitive pathways that involves activation by single electron transfer mediated by nascent Cu0 and degenerative chain transfer. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3283–3299, 2003
210 citations
TL;DR: A novel epoxy system was developed through the in situ curing of bisphenol A type epoxy and 4,4′-diaminodiphenylmethane with the sol-gel reaction of a phosphorus-containing trimethoxysilane (DOPO-GPTMS) as mentioned in this paper.
Abstract: A novel epoxy system was developed through the in situ curing of bisphenol A type epoxy and 4,4′-diaminodiphenylmethane with the sol–gel reaction of a phosphorus-containing trimethoxysilane (DOPO–GPTMS), which was prepared from the reaction of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) with 3-glycidoxypropyltrimethoxysilane (GPTMS). The preparation of DOPO–GPTMS was confirmed with Fourier transform infrared, 1H and 31P NMR, and elemental analysis. The resulting organic–inorganic hybrid epoxy resins exhibited a high glass-transition temperature (167 °C), good thermal stability over 320 °C, and a high limited oxygen index of 28.5. The synergism of phosphorus and silicon on flame retardance was observed. Moreover, the kinetics of the thermal oxidative degradation of the hybrid epoxy resins were studied. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2354–2367, 2003
157 citations
TL;DR: In this paper, polydisperse hyperbranched polyesters were modified for use as novel multifunctional reversible additionfragmentation chain-transfer (RAFT) agents, which were subsequently employed to synthesize star polymers of n-butyl acrylate and styrene.
Abstract: Polydisperse hyperbranched polyesters were modified for use as novel multifunctional reversible addition-fragmentation chain-transfer (RAFT) agents. The polyester-core-based RAFT agents were subsequently employed to synthesize star polymers of n-butyl acrylate and styrene with low polydispersity (polydispersity index 70%) and molecular weights [M-n > 140,000 g mol(-1), linear poly(methyl methacrylate) equivalents)], the corresponding styrene-based system reached a maximum molecular weight at low conversions (approximate to30%, M-n = 45,500 g mol(-1), linear polystyrene equivalents). The resulting star polymers were subsequently used as platforms for the preparation of star block copolymers of styrene and n-butyl acrylate with a polyester core with low polydispersities (polydispersity index < 1.25). The generated polystyrene-based star polymers were successfully cast into highly regular honeycomb-structured microarrays. (C) 2003 Wiley Periodicals, Inc.
139 citations
TL;DR: In this paper, the authors described the preparation of novolac-type phenolic resin/silica hybrid organic-inorganic nanocomposite, with a sol-gel process.
Abstract: This article describes the preparation of novolac-type phenolic resin/silica hybrid organic-inorganic nanocomposite, with a sol- gel process. The coupling agent was used to improve the interface between the organic and inorganic phases. The effect of the structure of the nanocomposite on its physical and chemical properties is dis- cussed. The coupling agent reacts with the resin to form covalent bonds. The structure of the modified hybrid nanocomposites was identified with a Fourier transform infrared spectroscope. The silica network was characterized by nuclear magnetic resonance imaging ( 29 Si NMR). Results revealed that Q4 (tetrasubstituted) and T3 (trisubstituted) are the dominant microstructures. The size of the silica in the phenolic resin was characterized with a scanning electron microscope. The size of the particles of inorganic silica in the modified system was less than 100 nm. The nanocomposite exhibited good transparency. Moreover, the thermal and mechanical properties exhibited significant improvement. The modified hybrid composite exhibited favorable thermal properties. The temperature at which a weight loss of 5% occurred increased from 281 to 350 °C. The flexural strength increased by 6 -30%. The limiting oxygen index of the nanocom- posite reached 37, and the Underwriters Laboratory test was 94V-0. Consequently, these materials possess excellent flame-retardant properties. © 2003 Wiley Periodicals,
136 citations
TL;DR: In this paper, the authors investigated the mechanism behind the termination of polymer growth and showed that at high concentrations of radicals, termination by radical recombination limits film growth, and that the removal of radical recombinations may also limit the film thickness.
Abstract: Although atom transfer radical polymerization (ATRP) is often a controlled/living process, the growth rate of polymer films during surface-initiated ATRP frequently decreases with time. This article investigates the mechanism behind the termination of film growth. Studies of methyl methacrylate and methyl acrylate polymerization with a Cu/tris[2-(dimethylamino)ethyl]amine catalyst system show a constant but slow growth rate at low catalyst concentrations and rapid growth followed by early termination at higher catalyst concentrations. For a given polymerization time, there is, therefore, an optimum intermediate catalyst concentration for achieving maximum film thickness. Simulations of polymerization that consider activation, deactivation, and termination show trends similar to those of the experimental data, and the addition of Cu(II) to polymerization solutions results in a more constant rate of film growth by decreasing the concentration of radicals on the surface. Taken together, these studies suggest that at high concentrations of radicals, termination of polymerization by radical recombination limits film growth. Interestingly, stirring of polymerization solutions decreases film thickness in some cases, presumably because chain motion facilitates radical recombination. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 386–394, 2003
TL;DR: In this paper, a kinetic model for reversible addition-fragmentation transfer (RAFT) polymerization with the method of moments was developed, which predicts the monomer conversion, number-average molecular weight, and polydispersity of the molecular weight distribution.
Abstract: A kinetic model has been developed for reversible addition-fragmentation transfer (RAFT) polymerization with the method of moments. The model predicts the monomer conversion, number-average molecular weight, and polydispersity of the molecular weight distribution. It also provides detailed information about the development of various types of chain species during polymerization, including propagating radical chains, adduct radical chains, dormant chains, and three types of dead chains. The effects of the RAFT agent concentration and the rate constants of the initiator decomposition, radical addition, fragmentation, disproportionation, and recombination termination of propagating radicals and cross-termination between propagating and adduct radicals on the kinetics and polymer chain properties are examined with the model.
TL;DR: In this article, the authors explain the estimates of k(f) similar to 10(4)/s and the choices of the rate constant in modeling based on experimental polymerization rate and radical concentration data, which appears to directly contradict the reported electron spin resonance (ESR) data in the range of <10(-6) mol/L.
Abstract: There has been an ongoing debate regarding the mechanism that causes rate retardation phenomena observed in some reversible addition-fragmentation transfer (RAFT) polymerization systems. Some attribute the retardation to slow fragmentation of adduct radicals, others attribute it to fast fragmentation coupled with cross-termination between propagating and adduct radicals. There exists a difference of six orders of magnitude (10(-2) versus 10(4)/s) in the reported values of the fragmentation rate constant (k(f0)) for virtually similar RAFT systems of PSt-S-C . (Ph)-S-PSt. In this communication, we explain the estimates of k(f) similar to 10(4)/s and the choices of the rate constant in modeling based on experimental polymerization rate and radical concentration data. The use of k(f) similar to 10(-2)/s in the model results in a calculated adduct radical concentration level of 10(-4) to 10(-3) mol/L, which appears to directly contradict the reported electron spin resonance (ESR) data in the range of <10(-6) mol/L. We hope that this open discussion can stimulate more effort to resolve this outstanding difference. (C) 2003 Wiley Periodicals, Inc.
TL;DR: In this paper, the authors argue that irreversible termination reactions are more likely to be a result of slow fragmentation of the intermediate macro-RAFT radical, which is stabilized by a phenyl group attached to the radical center or a poor leaving group.
Abstract: There is appreciable uncertainty concerning the magnitude of the fragmentation rate coefficient of the intermediate radical in reversible addition-fragmentation chain transfer (RAFT) polymerizations. A large proportion of the experimental and theoretical evidence suggests that it is a stable species with a lifetime longer than 0.0001 s. This is particularly the case when the intermediate macro-RAFT radical is stabilized by a phenyl group attached to the radical center or has a poor leaving group. Although the occurrence to some extent of irreversible termination reactions cannot be excluded, we argue that such reactions are more likely to be a result of slow fragmentation of the intermediate macro-RAFT radical.
TL;DR: The bulk polymerization of methyl methacrylate and styrene in the presence of an organically modified clay containing a vinyl group that can be involved in the polymerization produces exfoliated nanocomposites.
Abstract: The bulk polymerization of methyl methacrylate and styrene in the presence of an organically modified clay containing a vinyl group that can be involved in the polymerization produces exfoliated nanocomposites. These nanocomposites have been characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, mechanical properties, and cone calorimetry. The onset temperature of thermal degradation increases with the mechanical properties. The peak heat release rate is significantly reduced for nanocomposites containing 3 or 5% clay. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1124–1135, 2003
TL;DR: In this article, an ion-conductive mesogenic monomer with an imidazolium ionic moiety has been designed to obtain self-assembled materials forming ionic layers.
Abstract: An ion-conductive mesogenic monomer with an imidazolium ionic moiety has been designed to obtain self-assembled materials forming ionic layers. Self-standing polymer films are prepared by in situ photopolymerization of the monomer that forms homeotropic monodomain on a normal glass substrate in the smectic A phase. Macroscopically oriented, layered nanostructures are formed in the film. The ionic conductivity parallel to the smectic layer has been measured for the oriented film. In the smectic A phase at 150 °C, the magnitude of conductivity is about 10 - 2 S cm - 1 .
TL;DR: Several synthetic strategies for the incorporation of supramolecular binding units into polymers are described in this article, and general statements regarding metal complex stability are pre- sented as well as a special case representing the selective con- struction of heteroleptic terpyri-dine complexes.
Abstract: Several synthetic strategies for the incorporation of supramolecular binding units into polymers are described. Specifi- cally, terpyridine ligands have been introduced into polymers in such a way that they are distributed either randomly throughout the polymer backbone or at the chain end(s). Two terpyridine ligands form octahedral complexes with a variety of transition-metal ions, each having different properties. Some general statements regarding metal complex stability are pre- sented as well as a special case representing the selective con- struction of heteroleptic terpyri- dine complexes. This leads to a kind of LEGO system for connect- ing and disconnecting the polymer blocks via metal complexes. Me- tallo-supramolecular block copoly- mers, graft copolymers, and chain- extended polymers can be de- signed and prepared with the principles described. Once the de- sign parameters have been derived, thorough control over the final ma- terial and its properties can be gained. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1413- 1427, 2003
TL;DR: In this paper, temperature-sensitive poly(N-isopropylacrylamide) (PNIPAAm) hydrogels were synthesized with poly(ethylene glycol)s (PEGs; molecular weight = 2000-6000) as the pore-forming agents.
Abstract: Macroporous, temperature-sensitive poly(N-isopropylacrylamide) (PNIPAAm) hydrogels were synthesized with poly(ethylene glycol)s (PEGs; molecular weight = 2000–6000) as the pore-forming agents. The influence of the molecular weight and PEG content on the responsive kinetics of these macroporous hydrogels was investigated. The PEG-modified PNIPAAm hydrogels were characterized by the swelling ratio, deswelling–reswelling kinetics, Fourier transform infrared, and differential scanning calorimetry. The morphology of these hydrogels was analyzed with scanning electron microscopy. The prepared macroporous hydrogels exhibited some unique properties in comparison with the gels with low molecular weight PEGs (molecular weight < 2000) as the pore-forming agents. In addition, a preliminary study on the controlled release of bovine serum albumin from these macroporous hydrogels was carried out. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 152–159, 2003
TL;DR: In this article, statistical and block all-siloxane copolymers containing quaternary ammonium salt (QAS) groups with biocidal activity as lateral substituents were synthesized as models for the study of the effect of the arrangement of the QAS groups in the copolymer chain on their antimicrobial activity.
Abstract: Statistical and block all-siloxane copolymers containing quaternary ammonium salt (QAS) groups with biocidal activity as lateral substituents were synthesized as models for the study of the effect of the arrangement of the QAS groups in the copolymer chain on their antimicrobial activity. The bioactive siloxane unit was [3-n-octyldimethylammoniopropyl]methylsiloxane, and the neutral unit was dimethylsiloxane. The copolymers also contained siloxane units with unreacted precursor 3-chloropropyl or 3-bromopropyl groups. A small number of units containing highly hydrophilic 3-(3-hydroxypropyl-dimethylammonio)propyl groups were introduced to increase the solubility of the copolymers in water. The bioactive and bioneutral units were arranged in the polymer chain either in blocks or in statistical order. The block copolymers differed in the number and length of segments. The copolymers were obtained by the quaternization of tertiary amines by chloropropyl or bromopropyl groups attached to polysiloxane chains. The arrangement of the bioactive groups was controlled by the arrangement of the halogenopropyl groups in the bioactive copolymer precursor. All model siloxane copolymers showed high bactericidal activity in a water solution toward the gram-negative bacteria Escherichia coli and the gram-positive bacteria Staphylococcus aureus. However, no essential differences in the activities of the copolymers with block and statistical arrangements of units were detected.
TL;DR: In this paper, diamino-terminated poly(ethylene glycol) (PEG) was used to crosslink hyperbranched fluoropolymers (HBFPs).
Abstract: Hyperbranched fluoropolymers (HBFPs), based on benzyl ether linkages and having a large number of pentafluorophenyl chain ends, were crosslinked by a reaction with diamino-terminated poly(ethylene glycol) (PEG) or diamino-terminated poly(dimethyl siloxane) (PDMS) to form hyperbranched-linear copolymer networks of different compositions, structures, and properties. The crosslinking reactions involved the nucleophilic aromatic substitution of the pentafluorophenyl para-fluorines of HBFP by the amine functionalities of the respective telechelic linear segments. The contact angles, differential scanning calorimetry, thermogravimetric analysis, tensile measurements, and atomic force microscopy (AFM) were used to characterize the resulting network film samples. The surface wettability of the crosslinked materials was affected by the nature and amount of the linear polymer crosslinking agent employed. Amphiphilic polymer networks were formed by the incorporation of diamino-terminated PEG as a crosslinker, whereas diamino-terminated PDMS produced polymer networks of a hydrophobic character. The mechanical properties improved upon crosslinking, as measured by tensile testing. The mechanical integrity of the films was also found to improve upon crosslinking, as measured by AFM machining protocols. The AFM images revealed topographical morphologies that appeared to be the result of phase segregation of HBFP from PEG or PDMS; the dimensions of the phase-segregated domains were dependent on the stoichiometry of HBFP to the linear polymer and the thickness of the coating. As the content of PEG increased, fouling by human fibrinogen, used as a model protein, decreased. Further studies are in progress to determine the effects of the surface composition, morphology, and topography on the biofouling characteristics.
TL;DR: The first successful example of polycarbonate formation from 1-atm carbon dioxide and epoxide was demonstrated by the alternating copolymerization of carbon dioxide with manganese porphyrin as a catalyst as mentioned in this paper.
Abstract: The first successful example of the formation of polycarbonate from 1-atm carbon dioxide and epoxide was demonstrated by the alternating copolymerization of carbon dioxide and epoxide with manganese porphyrin as a catalyst. The copolymerization of carbon dioxide and cyclohexene oxide with (porphinato)manganese acetate proceeded under the 1-atm pressure of carbon dioxide to give a copolymer with an alternating sequence.
TL;DR: The reverse atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) was successfully carried out in 1-butyl-3-methylimidazolium hexafluorophosphate with 2,2-azobisisobutyronitrile/CuCl 2/bipyridine as the initiating system, which had been reported as not able to promote a controlled process of MMA in bulk as discussed by the authors.
Abstract: The reverse atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) was successfully carried out in 1-butyl-3-methylimidazolium hexafluorophosphate with 2,2-azobisisobutyronitrile/CuCl 2/bipyridine as the initiating system, which had been reported as not able to promote a controlled process of MMA in bulk. The living nature of the polymerization was confirmed by kinetic studies, end- group analysis, chain extension, and block copolymerization results. The polydispersity of the polymer obtained was quite narrow, with a weight-average molecular weight/ number-average molecular weight ratio of less than 1.2. In comparison with other reverse ATRPs in bulk or conventional solvents, a much smaller amount of the catalyst was used. After a relatively easy removal of the polymer and residue monomer, the ionic liquid and catalytic system could be reused without further treatment. © 2002 Wiley
TL;DR: In this article, the authors describe the development of optical pyrometry (OP) as a new analytical technique for the continuous monitoring of the progress of both free-radical and cationic photopolymerizations.
Abstract: This article describes the development of optical pyrometry (OP) as a new analytical technique for the continuous monitoring of the progress of both free-radical and cationic photopolymerizations. The method is rapid, reproducible, and very easy to implement. A temperature profile of a photopolymerization can be obtained. Preliminary studies have shown that the temperatures of some polymerizing monomers can easily reach temperatures in excess of 250 °C. The effects of the mass and reactivity of the monomer, light intensity, structures, and concentrations of the photoinitiators and monomers as well as the presence or absence of oxygen on various free-radical and cationic photopolymerizations were examined with this method. Coupling of real-time infrared spectroscopy with OP provides a convenient method for simultaneously monitoring both the chemical conversion and the temperature of a photopolymerization. This combined technique affords new insights into the effects of temperature-induced autoacceleration on the course of photopolymerizations.
TL;DR: In this article, sulfonated poly(phthalazinone ether ketone)s (SPPEKs) were obtained with a degree of sulfonation (DS) in the desired range of 0.6-1.2.
Abstract: As a novel class of proton exchange membrane materials for use in fuel cells, sulfonated poly(phthalazinone ether ketone)s (SPPEKs) were prepared by the modification of poly(phthalazinone ether ketone). Sulfonation reactions were conducted at room temperature with mixtures of 95–98% concentrated sulfuric acid and 27–33% fuming sulfuric acid with different acid ratios, and SPPEK was obtained with a degree of sulfonation (DS) in the desired range of 0.6–1.2. The presence of sulfonic acid groups in SPPEK was confirmed by Fourier transform infrared analysis, and the DS and structures were characterized by NMR. The introduction of sulfonic groups into the polymer chains increased the glass-transition temperature above the decomposition temperature and also led to an overall decrease in the decomposition temperature. Membrane films were cast from SPPEK solutions in N,N-dimethylacetamide. Water uptakes and swelling ratios of SPPEK membrane films increased with DS, and SPPEKs with DS > 1.23 were water-soluble at 80 °C. Proton conductivity increased with DS and temperature up to 95 °C, reaching 10−2S/cm. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 497–507, 2003
TL;DR: New degradable poly(ester anhydride)s were prepared by the melt polycondensation of diacid oligomers of poly(sebacic acid) (PSA) transesterified with ricinoleic acid via a melt bulk reaction between a high molecular weight PSA and ricinolesic acid.
Abstract: New degradable poly(ester anhydride)s were prepared by the melt polycondensation of diacid oligomers of poly(sebacic acid) (PSA) transesterified with ricinoleic acid The transesterification of PSA with ricinoleic acid to form oligomers was conducted via a melt bulk reaction between a high molecular weight PSA and ricinoleic acid A systematic study on the synthesis, characterization, degradation in vitro, drug release, and stability of these polymers was performed Polymers with weight-average molecular weights of 2000-60,000 and melting temperatures of 24-77 °C were obtained for PSA containing 20-90% (w/w) ricinoleic acid NMR and IR analyses indicated the formation of ester bonds along the polyanhydride backbone These new degradable copolymers have potential use as drug carriers
TL;DR: In this article, a review of advances in this emerging frontier of dendrimer science with a particular focus on covalent modifications is presented, including monomer design, syntheses, and properties of vari- ous dendritic backbone types.
Abstract: Chemists' fascina- tion with dendrimers mainly orig- inates from their unique architec- ture and its exploitation for the de- sign of well-defined functional macromolecules. Depending on the nature of the synthesis, func- tionalization is traditionally intro- duced at the core, the periphery, or both. However, the specific incor- poration of functional groups at the interior layers, i.e., generations, represents a considerable synthetic hurdle that must be overcome for the full potential of dendrimers to be realized. This review covers re- cent advances in this emerging frontier of dendrimer science with a particular focus on covalent modifications. Monomer design, syntheses, and properties of vari- ous dendritic backbone types are discussed. Internal functionaliza- tion dramatically increases the de- gree of complexity that can be implemented into a dendrimer macromolecule and, therefore, promises to lead to smart materials for future applications in bio- and nanotechnologies. © 2003 Wiley Peri-
TL;DR: New light-activated antimicrobial materials with a potentially wide range of possible uses in civilian settings were synthesized by the grafting of protoporphyrin IX and zinc protoporalin IX to nylon fibers, which showed increased antimicrobial activity against S. aureus with increasing exposure time.
Abstract: New light-activated antimicrobial materials with a potentially wide range of possible uses in civilian settings were synthesized by the grafting of protoporphyrin IX and zinc protoporphyrin IX to nylon fibers. These fibers were shown to be active against Staphylococcus aureus at light exposures of 10,000 lux and greater and against Escherichia coli at 60,000 lux. They were ineffective against both strains in the absence of light. At 40,000 lux, these fibers showed increased antimicrobial activity against S. aureus with increasing exposure time. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2297–2303, 2003
IBM1
TL;DR: The chemical amplification concept aimed at dramatically boosting the resist sensitivity was invented at IBM Research in San Jose, CA, in 1980 and was quickly employed in the manufacture of 1 megabit (Mbit) dynamic random access memory (DRAM) devices by deep ultraviolet (UV) (∼250 nm) lithography in IBM as mentioned in this paper.
Abstract: The chemical amplification concept aimed at dramatically boosting the resist sensitivity was invented at IBM Research in San Jose, CA, in 1980. The sensitivity enhancement is achieved by generating acid by irradiation, which induces a cascade of chemical transformations in a resist film. A chemically amplified resist based on acid-catalyzed deprotection was quickly employed in the mid-80s in manufacture of 1 megabit (Mbit) dynamic random access memory (DRAM) devices by deep ultraviolet (UV) (∼250 nm) lithography in IBM. The unexpectedly high-resolution capability of chemical amplification resists promoted their acceptance in the resist community and the microelectronics industry. All the advanced lithographic technologies (current workhorse 248 nm, maturing 193 nm, and emerging 157 nm, extreme UV, and projection electron beam) depend on chemical amplification resists. This article describes the invention, implementation in device manufacturing, current status, and future perspective of chemical amplification resists. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3863–3870, 2003
TL;DR: In this article, a bifunctional acrylamido-based reversible addition-fragmentation chain transfer (RAFT) chain-transfer agent (CTA) has been synthesized and used for the controlled free-radical polymerization of N,N-dimethylacrylamide (DMA).
Abstract: A novel bifunctional acrylamido-based reversible addition–fragmentation chain transfer (RAFT) chain-transfer agent (CTA), N,N′-ethylenebis[2-(thiobenzoylthio)propionamide] (CTA2), has been synthesized and used for the controlled free-radical polymerization of N,N-dimethylacrylamide (DMA). A comparative study of CTA2 and the monofunctional CTA N,N-dimethyl-s-thiobenzoylthiopropionamide (CTA1) has been conducted. Polymerizations mediated by CTA1 result in poly(N,N-dimethylacrylamide) (PDMA) homopolymers with unimodal molecular weight distributions, whereas CTA2 yields unimodal, bimodal, and trimodal distributions according to the extent of conversion. The multimodal nature of the PDMAs has been attributed to termination events and/or chains initiated by primary radicals. The RAFT polymerization of DMA with CTA2 also results in a prolonged induction period that may be attributed to the higher local concentration of dithioester functionalities early in the polymerization. A series of ω- and α,ω-dithioester-capped PDMAs have been prepared in organic media and subsequently employed as macro-CTAs for the synthesis of diblock and triblock copolymers in aqueous media with the zwitterionic monomer 3-[2-(N-methylacrylamido)-ethyldimethylammonio] propane sulfonate (MAEDAPS). Additionally, an ω-dithioester-capped MAEDAPS homopolymer has been used as a macro-CTA for the block polymerization of DMA. To our knowledge, this is the first example of a near-monodisperse, sulfobetaine-containing block copolymer prepared entirely in aqueous media. The diblock and triblock copolymers form aggregates in pure water that can be dissociated by the addition of salt, as determined by 1H NMR spectroscopy and dynamic light scattering. In pure water, highly uniform, micellelike aggregates with hydrodynamic diameters of 71–93 nm are formed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1262–1281, 2003
TL;DR: In this article, magnetite nanoparticles were obtained in the presence of poly(ethylene oxide) at the magnetite/monomer interface and the effect of the reaction medium polarity, the concentrations of the monomer, initiator, and stabilizer, and the temperature on the particle size, particle size distribution, and iron and oxirane group contents was studied.
Abstract: The precipitation of Fe 3 O 4 from an aqueous solution with ammonium hydroxide produced nanoparticles that were coated with a layer of oleic acid [or, in some cases, poly(ethylene oxide) or poly(vinylpyrrolidone)] before their dispersion into the organic phase. The encapsulation of magnetite nanoparticles in poly(2-hydroxyethyl methacrylate) or poly(2-hydroxyethyl methacrylate-co-glycidyl methacrylate) microparticles was achieved by dispersion polymerization in toluene/2-methylpropan-1-ol. Magnetic poly(glycidyl methacrylate) microparticles were obtained in the presence of poly(ethylene oxide) at the magnetite/monomer interface. The particles containing up to 20 wt % iron maintained their discrete nature and did not aggregate. The effect of the reaction medium polarity, the concentrations of the monomer, initiator, and stabilizer, and the temperature on the particle size, particle size distribution, and iron and oxirane group contents was studied.