bluuebunny/crossref_metadata_2025_split huggingface dataset:
Palladium‐ and platinum‐catalyzed coupling reactions of allyloxy aromatics with hydridosilanes and hydridosiloxanes: Novel liquid crystalline/organosilane materials
Authors: Sellinger Alan , Laine Richard M. , Chu Vano , Viney Christopher 
Published: April 2003

AbstractPt‐and Pd‐catalyzed reactions of a set of allyloxyaromatic mono‐and diesters with selected silanes were examined to develop simple, mild methods of forming liquid crystal (LC)/ siloxane and LC/silsesquioxane polymers. Pt complexes catalyze hydrosilylation to give primarily (≤ 80% selectivity at 100% conversion) terminal silylation of the allyloxys. The catalyst, platinum‐1,3‐divinyltetramethyldisiloxane [Pt (dvs), gives the cleanest reactions, fewest side products, under the mildest conditions. Model studies of Pt(dvs) catalyzed hydrosilylation of 4‐allyloxy methylbenzoate gave relative reactivities (HSiO1.5)8≫ Et3SiH > HMe2SiOSiMe2H > Ph2SiH2. The cubic silsesquioxane, (HSiO1.5)8, is so reactive hydrosilylation is over in 1–3 h at 0°C. All other reactions required > 40°C and longer reaction times. Initial efforts to form high polymers by Pt‐catalyzed reactions of bis‐allyloxy aromatics with Ph2SiH2provide polymers with bimodal MW distributions (polystyrene),Mws ≈ 30 kDa, and PDIs ≈ 5. Pd catalysis gives quite different products resulting from loss of propene with coincident formation of SiO bonds, “oxysilylation.” The same products appear (10–15%) in some Pt catalyzed reactions. Palladium dibenzylideneacetone/ Ph3P[Pd(dba)2/Ph3P], gives the cleanest oxysilylation reactions. Relative oxysilylation activities are: Ph2SiH2> HMe2SiOSiMe2H > Et3SiH. Polymerization with Pd catalysts provides polymers withMws ≈ 11 kDa, and PDIs ≈ 2. Reaction of 1 equiv. of (HSiO1.5)8with 4 equiv. of 4‐(4‐allyloxy‐benzoyloxy) biphenyl gives relatively pure tetrasubstituted LC/silsesquioxane [Mn≈ 1860 Da, PDI ≈ 1.09 (styrene equiv.) vs. 1746 Da caled.] A detailed analysis of the products formed, the catalytic reactivity patterns of the his (allyloxy) aromatic diesters and their LC transitions is presented. © 1994 John Wiley & Sons, Inc.
The antioxidant role of α‐tocopherol in polymers. I. The nature of transformation products of α‐tocopherol formed during melt processing of LDPE
Authors: Al‐Malaika S. , Ashley H. , Issenhuth S. 
Published: April 2003

AbstractThe antioxidant role of α‐tocopherol (vitamin E) in low‐density polyethylene (LDPE), and the nature of its transformation products formed during extrusion of the polymer are investigated. The melt stabilizing effectiveness of α‐tocopherol was found to be very high, higher than that of the commercial hindered phenol antioxidants, Irganox 1076 and 1010, after single and multiple extrusion. The high antioxidant activity of α‐tocopherol as a melt stabilizer is due, at least in part, to its transformation products. The importance of the processing history and the parent antioxidant concentration on the transformation products is discussed. Transformation products of α‐tocopherol were analyzed after each of the four extrusion passes of the polymer. These were fractionated, analyzed, and characterized by HPLC and spectroscopy, respectively. The main products formed are diastereoisomers of dimers and trimers, as well as aldehydes; the relative concentration of each was shown to depend on processing severity (number of extrusion passes) and the initial concentration of α‐tocopherol. The dihydroxydimer was found to be formed at a high concentration relative to the other products and proportional with the initial concentration of tocopherol. Based on both the identity and distribution of transformation products, a mechanism is proposed for the melt stabilization effect of α‐tocopherol in LDPE. © 1994 John Wiley & Sons, Inc.
Synthesis and characterization of maleimide polymers with pendant pyrazole groups. IV. Copolymerization of pyrazole‐modified maleimides with vinyl ethers
Authors: Ameduri Bruno , Boutevin Bernard , Malek Fouad 
Published: April 2003

AbstractThe synthesis of maleimides that have pyrazolic or bipyrazolic pendant groups is described. Their homopolymerization and their copolymerization with 2‐chloroethyl vinyl ether (CEVE) is reported. The homopolymerizations of such maleimides were performed under various conditions and led to low molecular‐weight polymers. However, alternating copolymers were obtained from CEVE as comonomers whatever the monomers feed compositions. A similar behavior was also observed for maleimides that do not exhibit any spacer, whereas for bulky vinyl ethers, random copolymers were produced. A comparison of the thermal behavior between these copolymers (glass transition temperatures, Tg, and decomposition temperatures) and other copolymers having different spacers between the nitrogenated cycles and the chain are related. Thus, an important decrease of Tg, was observed when C3H6CO2CH2 groups were used as the spacer instead of methylene groups. Moreover, the thermal weakness of these copolymers may come from the substituents of the vinyl ether and is discussed. © 1994 John Wiley & Sons, Inc.
Characterization of novel modified amorphous poly (ether sulphone)s
Authors: Maes C. , Devaux J. , Legras R. , Parsons I. W. , Mcgrail P. T. 
Published: April 2003

AbstractNew high‐temperature amorphous polymers with chlorine, amine, and maleimide chain‐ends have been synthesized by nucleophilic polycondensation and fully characterized by 13C‐NMR, 1H‐NMR, and potentiometric titration. From chain‐end determination, number average molecular masses were calculated. It was confirmed that transetherification during the synthesis led to a randomized polymer of the monomer residues. For nominally amine‐ended polymers obtained by addition of m‐aminophenol at the end of the synthesis, a small amount of hydroxyl chain‐ends was observed. This is ascribed also to transetherification. Complete reaction of the amine chain‐ends with maleic anhydride was demonstrated. Reaction of hydroxyl chain‐ends with acetic anhydride was also observed. The thermal stability of these different polymers was investigated; lower thermal stability was observed for amine and maleimide‐ended polymers. By two different methods, a Tg around 270d°C was determined for these novel amorphous aromatic polymers. © 1994 John Wiley & Sons, Inc.
The role of the triplet state in the photosensitization of cationic polymerizations by anthracene
Authors: Nelson E. W. , Carter T. P. , Scranton A. B. 
Published: April 2003

AbstractThe photosensitization mechanism for cationic polymerizations initiated by diaryliodonium salts photosensitized by anthracene was investigated using fluorescence and phosphorescence spectroscopy. In situ photosensitizer fluorescence measurements confirmed that the photosensitization reaction proceeds by an electron transfer process. Transient phosphorescence studies demonstrated that electron transfer occurred from the triplet excited state of anthracene to the initiator, with an intrinsic kinetic rate constant of 2 × 108 L/mol s. Further evidence for the role of the triplet state was provided by an observed seven‐fold decrease in the polymerization rate upon addition of a triplet state quencher. Finally, numerical solution of the photophysical kinetic equations indicated that the triplet state concentration was approximately three orders of magnitude higher than that of the singlet state, and that 94‐96% of the active cationic centers are produced by reaction of the initiator with the triplet state. These results indicate that the electron transfer occurs primarily from the triplet state of anthracene, with the singlet state providing only a minor contribution to the photosensitization reaction. © 1995 John Wiley & Sons, Inc.
Trimethylsilyl triflate as an initiator for cationic polymerization: Improved initiation through the use of promoters
Authors: Hrkach Jeffrey S. , Matyjaszewski Krzysztof 
Published: April 2003

AbstractTrimethylsilyl triflate (TMSOTf) can be used as an initiator for the cationic polymerization of alkenes and heterocycles. However, TMSOTf without additives and promoters acts inefficiently. Initiation in the cationic polymerization of tetrahydrofuran is slow because of unfavorable charge distribution in the trimethylsilyltetrahydrofuranium cation—a product of the reaction of monomer with TMSOTf. Acetone, 1,3‐dioxolane, and 1,2‐propylene oxide have been used as promoters to react with TMSOTf to create more reactive initiating species and to improve efficiency of initiation. Of these promoters, 1,2‐propylene oxide has been the most successful. When TMSOTf has been used to initiate the polymerization of 2‐methyl‐2‐oxazoline, unfavorable charge distribution in the N‐trimethylsilyl‐2‐methyl‐2‐oxiranium cation has produced an unreactive imine dimeric cation which extends the time required for polymerization to several weeks. 1,2‐Propylene oxide has been utilized to prevent formation of the imine dimeric cation by producing a more reactive initiating species. In the polymerization of isobutyl vinyl ether initiated by TMSOTf, 1,2‐propylene oxide has been shown to be ineffective as a promoter, but acetone can be used successfully. © 1995 John Wiley & Sons, Inc.
The effects of the charge density and structure of the polymer on the dye‐binding characteristics of some cationic polyelectrolytes
Authors: Vishalakshi B. 
Published: April 2003

AbstractThe interaction of various structurally different water‐soluble cationic polyelectrolytes with methyl orange, an anionic dye, has been studied. The changes in the UV‐Vis spectra of methyl orange in the presence of methyl and benzyl quaternized polyvinylpyridines and trialkylammonium and triphenylphosphonium salts of polyvinylbenzyl chloride have been used to investigate the effect of the structure on the dye‐binding characteristics of the polycations. The results are interpreted in the light of a simple theory of cooperative binding to a linear lattice. The extent of binding of the dye aggregates on the polymers has been calculated. The binding ability of the above‐mentioned polyelectrolytes has been found to depend on the nature of the substituent on the polycation. The contribution of the coulombic forces on binding of the dye by these polymers has been emphasized. © 1995 John Wiley & Sons, Inc.
Simulation model for the molecular weight distribution in emulsion polymerization
Authors: Tobita Hidetaka , Takada Yuko , Nomura Mamoru 
Published: April 2003

AbstractA Monte Carlo simulation model for the kinetics of emulsion polymerization is proposed. In the present model, the formation of each polymer molecule is simulated by the use of only a couple of probability functions; therefore, the calculation can be handled well even on personal computers. It is straightforward to account for virtually any kinetic event, such as the desorption of oligomeric radicals and chain length dependence of kinetic parameters, and as a consequence very detailed information such as the full distributions of the dead polymer molecular weights and the macroradicals among various polymer particles can be obtained. When bimolecular terminations are the dominant chain stoppage mechanism, the instantaneous molecular weight distribution (produced in a very small time interval) becomes broader than that for homogeneous polymerizations due to a higher possibility that short and long polymer radicals react with each other if bimolecular reactions are fast enough. The increase in the polydispersity of the MWD is fairly large, especially when bimolecular termination by disproportionation is significant; however, the gel permeation chromatography (GPC) may not be a suitable analytical technique to detect such broadening since oligomeric peaks may not be observed in the elution curve. The present simulation method provides greater insight into the complicated phenomena of emulsion polymerizations. © 1995 John Wiley & Sons, Inc.
Synthesis and characterization of bismaleimide–polyurethane crosslinked copolymers
Authors: Liao D. C. , Hsieh K. H. , Kao S. C. 
Published: April 2003

AbstractA series of novel crosslinked copolymers of bismaleimide (BMI) and polyurethanes (PU) were prepared by direct copolymerization of BMI monomer and urethane‐modified bismaleimide (UBMI). The copolymers were characterized by FT‐IR and solid state 13C‐NMR. The reaction rate of the BMI monomer can be significantly increased by copolymerization with UBMI. The crosslinked copolymers show good mechanical properties and high thermal stability. Studies on glass transition temperatures and dynamic mechanical properties indicate that the copolymer is a homogeneous system as the polyester‐type PU employed. The transmission electron microscopy (TEM) of the copolymer illustrated a one‐phase structure of the cured resins when the polyester‐type PU was incorporated. © 1995 John Wiley & Sons, Inc.
Factors affecting propagating fronts of addition polymerization: Velocity, front curvature, temperatue profile, conversion, and molecular weight distribution
Authors: Pojman John A. , Willis Jason , Fortenberry Dionne , Ilyashenko Victor , Khan Akhtar M. 
Published: April 2003

AbstractSeveral properties of propagating fronts of addition polymerization were studied. A power function could be fit to the velocity dependence on initiator concentration, but not with the exponents predicted by current models or in agreement with other published work. Bubbles from the volatile by‐products of initiator decomposition were found to affect the front velocity and curvature. The front velocity for triethylene glycol dimethacrylate polymerization was found to depend linearly on temperature over a moderate range. The conversion of methacrylic acid in fronts varied greatly with initiator type and concentration. Benzoyl peroxide produced much lower conversion than t‐butyl peroxide, but fronts with tBPO propagated slower. A dual initiator system of BPO and tBPO produced rapidly propagating fronts with good conversion but the contribution of each initiator to the velocity was not additive. The possibility of chain branching was considered. The apparent molecular weight distributions were very broad, often trimodal, and found to depend on initiator type and concentration as well as the tube diameter. The temperature profiles were measured and found to be very sharp for BPO and broader for tBPO but both had front temperatures in excess of 200°C, indicating a high ceiling temperature. © 1995 John Wiley & Sons, Inc.
Effect of stoichiometry and diffusion on an epoxy/amine reaction mechanism
Authors: Finzel Mark C. , Delong John , Hawley Martin C. 
Published: April 2003

AbstractThe bulk phase kinetics of an epoxy (DGEBA) /amine (DDS) thermoset have been studied using DSC, FTIR, and 13C‐NMR. In the absence of catalyst, the reaction was found to involve a main exothermic reaction between epoxide and amine hydrogen and a side reaction between tertiary amine formed in the main reaction and epoxide. The main reaction was exothermic while the side reaction had no discernable exotherm. Etherification did not occur to any significant extent. Since only the main reaction is exothermic, DSC was very useful for studying the main reaction kinetics. FTIR was used for determining whether epoxide and amine hydrogen were consumed at different rates as a way of following the side reaction. An IR band previously unused by other investigators was used to monitor the amine hydrogen concentration. NMR confirmed the above mechanism by identifying the formation of a quaternary ammonium ion/alkoxide ion pair as a reaction product of tertiary amine and epoxide. This mechanism has been successfully fit to a rate law valid over the entire extent of reaction. The rate constant for the epoxy/amine addition reaction was found to depend on hydroxide concentration (extent), reaction temperature, and glass transition temperature and included contributions from uncatalyzed and autocatalyzed parts. The side reaction (quaternary ammonium ion formation) formed weak bonds which did not affect the overall system Tg. Both reactions were second order. The rate constants for the main reaction first increase with increasing extent due to autocatalysis by hydroxide before decreasing due to the diffusion limit caused by gelation and vitrification. © 1995 John Wiley & Sons, Inc.
Polycarbonate synthesis by the melt phase carbonate‐ester interchange reaction of bisphenol‐A diacetate with dimethyl carbonate
Authors: Deshpande M. M. , Jadhav A. S. , Gunari A. A. , Sehra J. C. , Sivaram S. 
Published: April 2003

AbstractThe molecular weight of polycarbonate formed by the carbonate‐ester interchange reaction of bisphenol‐A diacetate (BPAC2) and dimethyl carbonate (DMC) was found to depend on the composition of the oligomer formed in its first stage. At a [DMC] : [BPAC2] ratio of 2, an oligomer with relatively higher acetate end group concentration was formed. This upon further polycondensation yielded a polycarbonate of inherent viscosity, 0.2‐0.25 dL/g. Upon addition of DMC at a later stage in the oligomer‐forming reaction, an oligomer containing relatively higher carbonate end groups could be obtained. These oligomers gave polycarbonates higher inherent viscosity, 0.4‐0.5 dL/g. It is therefore proposed that oligomers having carbonate end groups are more reactive in self‐polycondensation than those containing acetate end groups. © 1995 John Wiley & Sons, Inc.
Synthesis of poly(4‐vinylbenzocyclobutene) and its reaction with dienophiles
Authors: Endo Takeshi , Koizumi Toshio , Takata Toshikazu , Chino Keisuke 
Published: April 2003

Abstract4‐Vinylbenzocyclobutene (1) was prepared by the nickel‐catalyzed coupling reaction of 4‐bromobenzocyclobutene with vinylbromide in 70% yield. Radical homopolymerization of 1 at 60°C for 24 h afforded poly(4 vinylbenzocyclobutene) [poly(1)] in 89% yield and radical copolymerizations of 1 with styrene (St) or methyl methacrylate (MMA) were carried out to obtain the corresponding copolymers. The Q = 1.07, e = 0.046. As a model reaction of the polymer reaction of the polymer reaction of poly(1) and poly(4‐vinylbenzocyclobutene‐co‐styrene) [copoly(1‐St)] with dienophiles, the Diels‐Alder reaction of benzocyclobutene with N‐phenylmaleimide (MI) or maleic anhydride (MANH) was carried out to determine the optimum reaction conditions. Under the optimum condition, the Diels‐Alder reaction of poly(1) and copoly(1‐St) with MI and MANH in the presence of 4‐tert‐butyl‐catechol as an inhibitor were carried out to yield the corresponding polymers in good yields. The properties (solubilities, Tg, and temperature of 10% weight loss) of the products obtained from the polymer reaction were different from these of poly(1). © 1995 John Wiley & Sons, Inc.
Biodegradable polymers derived from natural fatty acids
Authors: Domb Abraham J. , Nudelman Raphael 
Published: April 2003

AbstractA new class of polyanhydrides synthesized from nonlinear hydrophobic fatty acid esters, based on ricinoleic, maleic acid, and sebacic acid, possessed desired physico‐chemical and mechanical properties for use as drug carriers. The polymers were synthesized by melt condensation to yield film‐forming polymers with molecular weights exceeding 100,000. Their rate of elimination from rats in the course of about 2 months was faster than that found for similar polyanhydrides previously tested. In vitro studies showed that these polymers underwent rapid degradation in the first 10 days. The drug release followed first‐order kinetics, showing a rapid drug release rate in the first 10 days which correlated with the degradation of the polymers. The fatty acid ester monomers underwent in vitro enzymatic degradation to the natural starting acids. Tests in rats demonstrated their toxicological inertness and biodegradability. © 1995 John Wiley & Sons, Inc.
Synthesis and characterization of new poly(arylene ether)s containing heterocyclic units. II.
Authors: Bottino Francesco A. , DiPasquale Giovanna , Leonardi Nicoletta , Pollicino Antonino 
Published: April 2003

AbstractA series of new poly(arylene ether)s, containing naphthalene, pyridine, and quinoline units have been prepared by solution condensation polymerization. The synthesis involves nucleophilic displacement of aromatic dihalides with aromatic potassium bisphenates in an anhydrous dipolar aprotic solvent at elevated temperatures. The polymers, having inherent viscosity from 0.24 to 1.32 dL/g, were obtained in quantitative yield, have excellent thermal stability as shown by 10% weight loss temperatures in nitrogen and air (above 450 and 430°C, respectively) and high glass transition temperatures (in the range of 150–220°C). The introduction of quinoline moieties in the polymer backbone positively influences the thermal properties, such as high Tg/Tm ratios. © 1995 John Wiley & Sons, Inc.
Peroxide crosslinking of linear low‐density polyethylenes with homogeneous distribution of short chain branching
Authors: Sajkiewicz P. , Phillips P. J. 
Published: April 2003

AbstractExtraction and swelling experiments were carried out in order to measure the crosslinkability by dicumyl peroxide (DCP) of new homogeneous linear low‐density polyethylenes (LLDPEs) with different molecular weight, branch content, and length of branches. Considering that the tertiary radicals are most probable macroradicals, our results indicate that tertiary carbons in LLDPEs could be either sites for scission reaction of effective coupling, depending upon degree of branching and to a lesser extent on degree of crosslinking. In the range of branching between 16 and n CH3/1000 C (n − 31 for low DCP concentration and decreases with DCP content approaching the value of 23 for the range above ca. 6 DCP moles per number average PE mole), the tertiary carbons seem to be rather the sites for effective coupling. In this range of branching an increase of crosslinkability with branch concentration and molecular weight of PE is due to the increase of crosslinking efficiency, but the scission probability is very low. At branch content exceeding the value of n CH3/1000 C, the dominant reaction on tertiary carbons is scission, leading to a small decrease of crosslinkability with increasing branch content. The possible mechanisms favoring tertiary carbons for either coupling or scission are discussed. © 1995 John Wiley & Sons, Inc.
Reactions of hydroxyl (HO•) and hydroperoxyl (HO) radicals generated chemically and photochemically with poly(ethylene oxide)
Authors: Kaczmarek H. , Lindén L. Å. , Rabek J. F. 
Published: April 2003

AbstractPoly(ethylene oxide) (poly(oxy‐1,2‐ethanediyl) is rapidly oxidized by hydroxyl (HO•) and hydroperoxyl (HO) radicals generated by photolysis of hydrogen peroxide (H2O2) or by the catalytic decomposition of H2O2by metallic silver. This process is accompanied by a chain scission during which the molecular weight decreases and the polydispersity changes. As a result of this process, the crystalline structure of poly(ethylene oxide) disappears, and the polymer becomes completely amorphous. © 1995 John Wiley & Sons, Inc.
Spectrophotometric determination of thermal transition of polymeric systems using photochromic probes
Authors: Nayak Biswabimohan , Gupta Satyendra Nath 
Published: April 2003

AbstractMercury‐dithizone complex both free and bonded to a polymeric system has been synthesized and used to measure the thermal transition of polystyrene, poly(vinyl acetate), and some other polymers. The thermal relaxation rate of the activated complex in dark has been found to be dependent on the free volume of a polymer matrix. The rate goes through a maximum above Tg of a polymer. A very sensitive method, based on thermal recovery of activated photochromic probe chromophore has been devised to measure the thermal transition of both single and multicomponent polymer matrices. © 1995 John Wiley & Sons, Inc.