bluuebunny/crossref_metadata_2025_split huggingface dataset:
Silicone‐based impact modifiers for poly(vinyl chloride), engineering resins, and blends
Authors: Yanagase Akira , Ito Masakazu 
Published: January 2004

AbstractSilicone‐based impact modifiers were prepared in a previous study. The modifiers were composed of silicone/acrylic rubber cores and grafted acrylic shells. They improved the toughness of poly(vinyl chloride) (PVC) and poly(methyl methacrylate). The silicone emulsion that was used to produce the silicone‐based impact modifiers was prepared via two routes: emulsion polymerization and bulk polymerization of octamethyltetracyclosiloxane. Many silicone‐based impact modifiers were produced that had different silicone/acrylic rubber characteristics. Through a toughness examination of modified PVC, the best composition of the silicone‐based impact modifiers was obtained, and the silicone content in the rubber composition was 25 wt %. The morphology of the silicone‐based impact modifiers, determined by transmission electron microscopy, was as follows: core and second shell polymers were mainly poly(butyl acrylate), and the first shell polymer was silicone. The silicone‐based impact modifiers were blended with engineering resins such as PVC, polycarbonate (PC), poly(butylene terephthalate) (PBT), and PC/PBT mixtures. The impact strength under standard conditions and after weathering test conditions for blends of the silicone‐based impact modifiers were investigated with respect to two commercially available acrylic and methyl methacrylate/butadiene/styrene impact modifiers. The results showed good weatherability and good toughness under low‐temperature conditions for the silicone‐based impact modifiers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1112–1119, 2004
Effect of the crosslink density on the morphology and properties of reaction‐injection‐molding poly(urethane urea) elastomers
Authors: Li Zaifeng , Yang Guanghua , Xu Chunming 
Published: January 2004

AbstractThe effect of the crosslink density on the morphology and properties of reaction‐injection‐molding poly(urethane urea) (PUU) elastomers was investigated. Fourier transform infrared spectroscopy data showed that the linear and crosslinked PUU had entirely different hard‐domain sizes and hard‐segment ordering. A study of the morphology indicated that an increase in the crosslink density increased microphase mixing. Differential scanning calorimetry studies indicated that the hard‐segment initial glass‐transition temperature was independent of the crosslink density. The glass‐transition temperature of the soft segment was highest when the network was perfect. The tensile‐strength behavior showed that the mechanical properties of PUU reached a maximum when the network was perfect. The increase in the resilience of the crosslinked PUU elastomer was higher than that of the linear PUU elastomer with an increase in temperature, and the reduction of the hardness of the former was also higher than that of the latter. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1126–1131, 2004
Performance of various activators in ethylene polymerization based on an iron(II) catalyst system
Authors: Wang Qi , Yang Huaxiang , Fan Zhiqiang , Xu Hong 
Published: January 2004

AbstractEthylisobutylaluminoxane (EBAO) and its analogues were synthesized by a reaction between an triethylaluminum (Et3Al)/triisobutylaluminum (i‐Bu3Al) mixture and 4‐fluorobenzeneboronic acid, phenylboronic acid, or n‐butaneboronic acid and subsequent hydrolysis with water. They were used as cocatalysts in ethylene polymerization catalyzed by an iron complex {[(ArNC(Me))2C5H3N]FeCl2, where Ar is 2,6‐diisopropylphenyl}. Polyethylene with a high molecular weight and a narrow molecular weight distribution was prepared with modified EBAOs, and the performance of the iron complex at high polymerization temperatures was greatly improved. The activators for the iron complex also affected the polymerization activity and the molecular weight of the resultant polyethylene. It was suggested that the stereo and electronic effects of the substitute groups of aluminoxane contributed to the improved performance of the new activators. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1093–1099, 2004
New blue electroluminescent n‐type polyfluorene copolymers with a 1,3,4‐oxadiazole unit in the main chain
Authors: Yang Nam Choul , Lee Sang Min , Yoo Young Man , Kim Jai Kyeong , Suh Dong Hack 
Published: January 2004

AbstractNovel polyfluorene copolymers alternately having an 1,3,4‐oxadiazole unit in the main chain were prepared by both one‐step and two‐step methods for polyoxadiazole synthesis. They displayed highly efficient blue photoluminescence, the properties of which were affected by the extent of conjugation and the changes in the electron density by a side chain. An electrochemical analysis of the polymers using cyclic voltammetry suggested that they could be used as electron‐transport/hole‐blocking materials as well as blue emission materials for polymer light‐emitting diodes. A simple double‐layer device consisting of poly(N‐vinylcarbazole) as a hole‐transport layer and poly[(9,9′‐didodecylfluorene‐2,7‐diyl)‐alt‐((1,4‐bis(1,3,4‐oxadiazole)‐2,5‐di(2‐ethylhexyloxy)phenylene)‐5,5′‐diyl)] as an emission layer exhibited narrow blue electroluminescence with a maximum at 430 nm. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1058–1068, 2004
Fluorescent probes for monitoring the pulsed‐laser‐induced photocuring of poly(urethane acrylate)‐based adhesives
Authors: Peinado Carmen , Salvador Enrique F. , Corrales Teresa , Bosch Paula , Catalina Fernando 
Published: January 2004

AbstractFluorescence spectroscopy was used to study the kinetics of polymerization of acrylic adhesive formulations exposed to a 355‐nm pulsed emission from an Nd‐YAG laser. Nine fluorescent probes were used for monitoring the laser curing, showing different sensitivities. In general, the fluorescence intensity emission increased as crosslinking occurred. In addition, solvatochromic fluorescent probes showed a blueshift in their emission. A relative method was applied for the evaluation of the polymerization rates in three different acrylic systems. Special features of pulsed‐laser‐induced polymerization were treated in detail, such as the influence of the laser pulse frequency and the incident laser beam intensity. The polymerization rate slowed down as the pulse repetition rate decreased. An inhibition period due to oxygen quenching was observed, and it was highly dependent on the laser repetition rate and the nature of the photoinitiator. The effect of the laser beam intensity on the kinetics of such fast reactions was studied. In general, increasing the laser energy improved the rate of polymerization. The degree of cure improved as the polymerization rate increased as a result of faster crosslinking, rather than relaxation volume kinetics. Moreover, a saturation rate effect occurred that depended on the photoinitiator. The different behaviors of the two photoinitiators in the curing of the same acrylic formulation was explained on the basis of primary radical termination. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1227–1238, 2004
Measurement of the dissolved oxygen concentration in acrylate monomers with a novel photochemical method
Authors: Gou Lijing , Coretsopoulos Chris N. , Scranton Alec B. 
Published: January 2004

AbstractBecause of the well‐known radical‐scavenging behavior, molecular oxygen is capable of inhibiting free‐radical chain polymerizations of unsaturated monomers. The deleterious effects of diffused oxygen in a polymerization system result in both a reduced polymerization rate and the loss of surface properties of a polymer film or coating. However, reliable data for oxygen concentration in organic monomers are relatively scarce because of the experimental and instrumental limitations of the commercially available techniques. In this study, a photochemical method was developed and was used to obtain the dissolved oxygen concentration in seven acrylate monomers. The principle of the method was to convert ground‐state molecular oxygen dissolved in monomer to the excited, singlet‐state oxygen and then react the singlet oxygen with a third compound (singlet oxygen trapper). By monitoring the concentration of this singlet oxygen trapper spectrophotometrically, the concentration of dissolved oxygen can be obtained with the established stoichiometry for the reaction between singlet oxygen and trapper. The singlet oxygen concentrations in the acrylate monomers varied from 0.59 to 2.07 × 10−3 mol/L, depending on the monomer structure. The strategies and considerations for generalizing the method to other systems, including highly oxygenated organics, are discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1285–1292, 2004
Copper‐mediated radical polymerization on a microcellular monolith surface
Authors: Moine Laurence , Deleuze Hervé , Degueil Marie , Maillard Bernard 
Published: January 2004

AbstractHigh‐capacity microcellular monoliths were prepared by a two‐step process, including the synthesis of a bromoester‐functionalized scaffold by the copolymerization of a highly concentrated emulsion and an in situ surface polymerization of methyl methacrylate with atom transfer radical polymerization. The influence of various parameters, such as the feed ratio, the concentration of immobilized bromoester groups, and the presence of a spacer group on the poly(methyl methacrylate) loading, was studied. Monoliths with capacities of up to 7 mmol g−1 were obtained. Thermogravimetric analyses, scanning electron microscopy experiments, and mercury intrusion porosimetry measurements were used for the characterization of the final materials. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1216–1226, 2004
Preparation and properties of poly(N‐isopropylacrylamide)/poly(N‐isopropylacrylamide) interpenetrating polymer networks for drug delivery
Authors: Zhang Jian‐Tao , Huang Shi‐Wen , Cheng Si‐Xue , Zhuo Ren‐Xi 
Published: January 2004

AbstractA novel poly(N‐isopropylacrylamide) (PNIPA)/PNIPA interpenetrating polymer network (IPN) was synthesized and characterized. In comparison with conventional PNIPA hydrogels, the shrinking rate of the IPN hydrogel increased when gels, swollen at 20 °C, were immersed in 50 °C water. The phase‐transition temperature of the IPN gel remained unchangeable because of the same chemical constituent in the PNIPA gel. The reswelling kinetics were slower than those of the PNIPA hydrogel because of the higher crosslinking density of the IPN hydrogel. The IPN hydrogel had better mechanical strength because of its higher crosslinking density and polymer volume fraction. The release behavior of 5‐fluorouracil (5‐Fu) from the IPN hydrogel showed that, at a lower temperature, the release of 5‐Fu was controlled by the diffusion of water molecules in the gel network. At a higher temperature, 5‐Fu inside the gel could not diffuse into the medium after a burst release caused by the release of the drug on the surface of the gel. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1249–1254, 2004
Poly(phenylene vinylene)‐based copolymers containing 3,7‐phenothiazylene and 2,6‐pyridylene chromophores: Fluorescence sensors for acids, metal ions, and oxidation
Authors: Wu Tzi‐Yi , Chen Yun 
Published: January 2004

AbstractA novel copolymer, poly(N‐hexyl‐3,7‐phenothiazylene‐1,2‐ethenylene‐2,6‐pyridylene‐1,2‐ethenylene) (P3), containing N‐hexyl‐3,7‐phenothiazylene and 2,6‐pyridylene chromophores was synthesized to investigate the effect of protonation, metal complexation, and chemical oxidation on its absorption and photoluminescence (PL). Poly(N‐hexyl‐3,8‐iminodibenzyl‐1,2‐ethenylene‐1,3‐phenylene‐1,2‐ethenylene) and poly(N‐hexyl‐3,7‐phenothiazylene‐1,2‐ethenylene‐1,3‐phenylene‐1,2‐ethenylene) (P2), consisting of 1,3‐divinylbenzene alternated with N‐hexyl‐3,8‐iminodibenzyl and N‐hexyl‐3,7‐phenothiazylene, respectively, were also prepared for comparison. Electrochemical investigations revealed that P3 exhibited lower band gaps (2.34 eV) due to alternating donor and acceptor conjugated units (push–pull structure). The absorption and PL spectral variations of P3 were easily manipulated by protonation, metal chelation, and chemical oxidation. P3 displayed significant bathochromic shifts when protonated with trifluoroacetic acid in chloroform. The complexation of P3 with Fe3+ led to a significant absorption change and fluorescence quenching, and this implied the coordination of ferric ions with the 2,6‐pyridylene groups in the backbone. Moreover, both phenothiazylene‐containing P2 and P3 showed conspicuous PL quenching with a slight redshift when oxidized with NOBF4. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1272–1284, 2004
Emulsion polymerization: From fundamental mechanisms to process developments
Authors: Asua José M. 
Published: January 2004

AbstractEmulsion polymers are “products by process” whose main properties are determined during polymerization. In this scenario of margins reduction, increasing competition, and public sensitivity to environmental issues, the challenge is to achieve an efficient production of high‐quality materials in a consistent, safe, and environmentally friendly way. This highlight reviews the investigations carried out at The University of the Basque Country to develop a knowledge‐based strategy to achieve these goals. First, the research in fundamental mechanisms is discussed. This includes studies in radical entry and exit, oil‐soluble initiators, propagation‐rate constants of acrylic monomers, processes involved in the formation of branched and crosslinked polymers, microstructure modification by postreaction operations, the formation of particle morphology, and reactive surfactants. The advanced mathematical models developed in the group are also reviewed. In the second part, the advances in process development (optimization, online monitoring and control, monomer removal, production of high‐solids, low‐viscosity latices, and process intensification) are presented. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1025–1041, 2004
From analysis of protein structural alignments toward a novel approach to align protein sequences
Authors: Sunyaev Shamil R. , Bogopolsky Gennady A. , Oleynikova Natalia V. , Vlasov Peter K. , Finkelstein Alexei V. , Roytberg Mikhail A. 
Published: January 2004

AbstractAlignment of protein sequences is a key step in most computational methods for prediction of protein function and homology‐based modeling of three‐dimensional (3D)‐structure. We investigated correspondence between “gold standard” alignments of 3D protein structures and the sequence alignments produced by the Smith–Waterman algorithm, currently the most sensitive method for pair‐wise alignment of sequences. The results of this analysis enabled development of a novel method to align a pair of protein sequences. The comparison of the Smith–Waterman and structure alignments focused on their inner structure and especially on the continuous ungapped alignment segments, “islands” between gaps. Approximately one third of the islands in the gold standard alignments have negative or low positive score, and their recognition is below the sensitivity limit of the Smith–Waterman algorithm. From the alignment accuracy perspective, the time spent by the algorithm while working in these unalignable regions is unnecessary. We considered features of the standard similarity scoring function responsible for this phenomenon and suggested an alternative hierarchical algorithm, which explicitly addresses high scoring regions. This algorithm is considerably faster than the Smith–Waterman algorithm, whereas resulting alignments are in average of the same quality with respect to the gold standard. This finding shows that the decrease of alignment accuracy is not necessarily a price for the computational efficiency. Proteins 2003;9999:000–000. © 2003 Wiley‐Liss, Inc.
Substrate binding to mononuclear metallo‐β‐lactamase from Bacillus cereus
Authors: Dal Peraro Matteo , Vila Alejandro J. , Carloni Paolo 
Published: January 2004

AbstractStructure and dynamics of substrate binding (cefotaxime) to the catalytic pocket of the mononuclear zinc‐β‐lactamase from Bacillus cereus are investigated by molecular dynamics simulations. The calculations, which are based on the hydrogen‐bond pattern recently proposed by Dal Peraro et al. (J Biol Inorg Chem 2002; 7:704–712), are carried out for both the free and the complexed enzyme. In the resting state, active site pattern and temperature B‐factors are in agreement with crystallographic data. In the complexed form, cefotaxime is accommodated into a stable orientation in the catalytic pocket within the nanosecond timescale, interacting with the enzyme zinc‐bound hydroxide and the surrounding loops. The β‐lactam ring remains stable and very close to the hydroxide nucleophile agent, giving a stable representation of the productive enzyme‐substrate complex. Proteins 2004;54:000–000. © 2003 Wiley‐Liss, Inc.
Comparison of the transition state ensembles for folding of Im7 and Im9 determined using all‐atom molecular dynamics simulations with ϕ value restraints
Authors: Paci Emanuele , Friel Claire T. , Lindorff‐Larsen Kresten , Radford Sheena E. , Karplus Martin , Vendruscolo Michele 
Published: January 2004

AbstractDelineation of the structural properties of transition states is key to deriving models for protein folding. Here we describe the structures of the transition states of the bacterial immunity proteins Im7 and Im9 obtained by all‐atom molecular dynamics simulations with ϕ value restraints derived from protein engineering experiments. This pair of proteins is of special interest because, at pH 7 and 10 °C, Im7 folds via an intermediate while Im9 folds with a two‐state transition. The structures of the transition states for Im7 and Im9, together with their radii of gyration and distances from the native state, are similar. The typical distance between any two members of the transition state ensemble of both proteins is large, with that of Im9 nearly twice that of Im7. Thus, a broad range of structures make up the transition state ensembles of these proteins. The ensembles satisfy the set of rather low ϕ values and yet are consistent with high βT values (> 0.85 for both proteins). For both Im7 and Im9 the inter‐helical angles are highly variable in the transition state ensembles, although the native contacts between helices I and IV are well conserved. By measuring the distribution of the accessible surface area for each residue we show that the hydrophobic residues that are buried in the native state remain buried in the transition state, corresponding to a hydrophobic collapse to a relatively ordered globule. The data provide new insights into the structural properties of the transition states of these proteins at an atomic level of detail and show that molecular dynamics simulations with ϕ value restraints can significantly enhance the knowledge of the transition state ensembles (TSE) provided by the experimental ϕ values alone. Proteins 2004;54:000–000. © 2003 Wiley‐Liss, Inc.
Prediction of protein relative solvent accessibility with support vector machines and long‐range interaction 3D local descriptor
Authors: Kim Hyunsoo , Park Haesun 
Published: January 2004

AbstractThe prediction of protein relative solvent accessibility gives us helpful information for the prediction of tertiary structure of a protein. The SVMpsi method, which uses support vector machines (SVMs), and the position‐specific scoring matrix (PSSM) generated from PSI‐BLAST have been applied to achieve better prediction accuracy of the relative solvent accessibility. We have introduced a three‐dimensional local descriptor that contains information about the expected remote contacts by both the long‐range interaction matrix and neighbor sequences. Moreover, we applied feature weights to kernels in SVMs in order to consider the degree of significance that depends on the distance from the specific amino acid. Relative solvent accessibility based on a two state‐model, for 25%, 16%, 5%, and 0% accessibility are predicted at 78.7%, 80.7%, 82.4%, and 87.4% accuracy, respectively. Three‐state prediction results provide a 64.5% accuracy with 9%; 36% threshold. The support vector machine approach has successfully been applied for solvent accessibility prediction by considering long‐range interaction and handling unbalanced data. Proteins 2004;54:000–000. © 2003 Wiley‐Liss, Inc.
Structural principles of leucine‐rich repeat (LRR) proteins
Authors: Enkhbayar Purevjav , Kamiya Masakatsu , Osaki Mitsuru , Matsumoto Takeshi , Matsushima Norio 
Published: January 2004

AbstractLRR‐containing proteins are present in over 2000 proteins from viruses to eukaryotes. Most LRRs are 20–30 amino acids long, and the repeat number ranges from 2 to 42. The known structures of 14 LRR proteins, each containing 4–17 repeats, have revealed that the LRR domains fold into a horseshoe (or arc) shape with a parallel β‐sheet on the concave face and with various secondary structures, including α‐helix, 310‐helix, and pII helix on the convex face. We developed simple methods to charactere quantitatively the arc shape of LRR and then applied them to all known LRR proteins. A quantity of 2Rsin(φ/2), in which R and φ are the radii of the LRR arc and the rotation angle about the central axis per repeating unit, respectively, is highly conserved in all the LRR proteins regardless of a large variety of repeat number and the radius of the LRR arc. The radii of the LRR arc with β‐α structural units are smaller than those with β‐310 or β‐pII units. The concave face of the LRR β‐sheet forms a surface analogous to a part of a Möbius strip. Proteins 2004;54:000–000. © 2003 Wiley‐Liss, Inc.
Is there a weak H‐bond → LBHB transition on tetrahedral complex formation in serine proteases?
Authors: Shokhen Michael , Albeck Amnon 
Published: January 2004

AbstractThe transformation of a weak hydrogen bond in the free enzyme into a low‐barrier hydrogen bond (LBHB) in the tetrahedral intermediate has been suggested as an important factor facilitating catalysis in serine proteases. In this work, we examine the structure of the H‐bond in the Asp102–His57 diad of serine proteases in the free enzyme and in a covalent tetrahedral complex (TC) with a trifluoromethylketone inhibitor. We apply ab initio quantum mechanical calculations to models consisting of a large molecular fragment of the enzyme active site, and the combined effect of the rest of the protein body and the solvation by surrounding bulk water was simulated by a self‐consistent reaction field method in our novel QM/SCRF(VS) approach. Potential profiles of adiabatic proton transfer in the Asp102–His57 diad in these model systems were calculated. We conclude that the hydrogen bond in both the free enzyme and in the enzyme‐inhibitor TC is a strong ionic asymmetric one‐well hydrogen bond, in contrast to a previous suggestion that it is a weak H‐bond in the former and a double‐well LBHB in the latter. Proteins 2004;54:000–000. © 2003 Wiley‐Liss, Inc.