bluuebunny/crossref_metadata_2025_split huggingface dataset:
Improved synthesis of polystyrene–poly(ethylene oxide)‐heparin block copolymers
Authors: Vulić I. , Loman A. J. B. , Feijen J. , Okano T. , Kim S. W. 
Published: April 2003

AbstractA novel procedure for the synthesis of block copolymers composed of a hydrophobic block of polystyrene, a hydrophilic block of poly(ethylene oxide) and a bioactive block of nitrous acid‐degraded heparin was developed. Amino‐semitelechelic polystyrene was prepared by anionic polymerization of styrene in cyclohexane, using sec‐butyllithium as initiator and N‐(benzylidene)trimethylsilylamide as terminator. After purification using preparative column chromatography, polystyrene with one amino group per chain and a narrow molecular weight distribution was obtained. The terminal amino group was used in the coupling reaction with amino‐telechelic poly(ethylene oxide) using toluene 2,4‐diisocyanate to produce amino‐semitelechelic polystyrene‐poly(ethylene oxide) diblock copolymer (PS‐PEO‐NH2). The block copolymer was purified by preparative column chromatographic separations and had a narrow molecular weight distribution. Approximately one amino group per chain was found. When methylene 4,4′‐diphenyl diisocyanate or hexamethylene diisocyanate were used as coupling agents low yields of PS‐PEO‐NH2 were obtained. Polystyrene‐poly(ethylene oxide)‐heparin triblock copolymer was synthesized in a DMF‐H20 (40:1, v/v) mixture by a coupling reaction of PS‐PEO‐NH2 with nitrous acid‐degraded heparin, in which aldehyde groups react with the primary amino groups of PS‐PEO‐NH2 at pH 7 in the presence of NaBH3CN via reductive amination. Using this procedure, 18–32% w/w heparin was incorporated, corresponding to ±1 PS‐PEO chain per heparin molecule. These procedures enable the synthesis of well defined heparin containing block copolymers, which will be further evaluated for thier blood compatibility.
Synthesis, decomposition, and initiator properties of macroazonitriles for the preparation of polymers with crown ether units
Authors: Tunca Umit , Yagci Yusuf 
Published: April 2003

AbstractMacroazonitriles containing crown ether moieties and various amounts of N  Nunits in the main chain were prepared by solution polycondensatio between cis‐diamino dibenzo‐18‐crown‐6 (DADC) and adipoyl chloride (AC) or terephtaloyl chloride (TPC) with the addition of 4,4′‐azobis(4‐cyanopentanyl chloride) (ACPC). Decomposition of the azo linkage present in the polyamides, obtained by using TPC, were studied by DSC. The rate constants and activation energies for the decomposition were determined and a small effect of terephtaloyl group on the rate was observed. The kinetics of the polymerization of styrene by the poly(azoamide), obtained from ACPC and DADC were investigated in DMSO.
Photo‐induced “charge transfer” copolymerizations of donor monomers with acceptor monomers by irradiating their CT complexes
Authors: Li Tong , Lou Bin , Chu Guobei , Hall H. K. 
Published: April 2003

AbstractThe photo‐induced “charge‐transfer” copolymerization of various donor monomer‐acceptor monomer pairs was studied by irradiation of their CT complexes with 365 nm light. The influence of the donor and acceptor strength on the rate of polymerization shows that stronger donor/weaker acceptor pairs or weaker donor/stronger acceptor pairs favor copolymerization. The proposed initiation mechanism involves the formation of an excited complex, which then collapses to the tetramethylene diradical for initiation of free radical copolymerizations.
Grafting of polyesters from ultrafine inorganic particles: Copolymerization of epoxides with cyclic acid anhydrides initiated by COOK groups introduced onto the surface
Authors: Tsubokawa Norio , Kogure Akira , Sone Yasuo 
Published: April 2003

AbstractThe grafting of polyesters onto ultrafine inorganic particles, such as silica, titanium oxide, and ferrite, by use of potassium carboxylate (COOK) groups introduced onto the surface was investigated. The introduction of COOK groups onto the surface was achieved by the neutralization of acid anhydride groups, which were introduced by the reaction of 4‐trimethoxysilyltetra‐hydrophthalic anhydride with hydroxy groups on the surface: the amount of COOK groups introduced onto the surface of silica, titanium oxide, and ferrite was estimated to be 1.92, 0.94, and 0.62 mmol/g, respectively. It was found that the anionic ring‐opening copolymerization of epoxides with cyclic acid anhydrides is initiated by COOK groups introduced onto the surface. In the polymerization, polyester formed was effectively grafted onto the surface based on the propagation of the polymer from COOK groups on the surface: the percentage of grafting of polyester from chloromethyloxirane and phthalic anhydride onto silica, titanium oxide, and ferrite reached to 118.3, 82.1, and 7.5%, respectively. The rate of the polymerization and percentage of grafting increased with an increase in COOK group content of the ultrafine particles. The grafting of polyester onto these particles was confirmed by infrared spectroscopy. Polyester‐grafted ultrafine particles produced a stable colloidal dispersion in organic solvent.
Direct polycondensation of 4,4′‐azobis‐4‐cyanopentanoic acid with diols and diamines using 1‐methyl‐2‐chloropyridinium iodide
Authors: Matsukawa Kimihiro , Ueda Akira , Inoue Hiroshi , Nagai Susumu 
Published: April 2003

AbstractPolyesters and polyamides derived from 4,4′‐azobis‐4‐cyanopentanoic acid (ACPA) were prepared by the direct polycondensation using 1‐methyl‐2‐chloropyridinium iodide (MCPI) as a condensation reagent at room temperature, in which the azo group was not decomposed. These polyesters and polyamides containing the azo groups could be used for effective initiators of radical polymerizations with some vinyl monomers.
Anionic polymerization of lactones initiated by alkali graphitides. V. Initiation mechanism and nature of the active centers
Authors: Gitsov Ivan , Rashkov Iliya B. , Panayotov Ivan M. 
Published: April 2003

AbstractThe initiation mechanism of the anionic polymerization of ϵ‐caprolactone (ϵ‐CL) under the action of the potassium graphitide KC24 was studied by 1H‐NMR spectroscopy of low molecular weight products of the polymerization. On the basis of the experimental results, the assumption was made that the initiation proceeds through a proton transfer from the monomer to the initiator. From the results of end group analysis it was assumed that the active centers of the growing polymer chain are of an alcoholate type. Comparative investigations were performed on the mechanism of ϵ‐CL polymerization under the action of anion‐radicals (potassium‐naphthylide) and alkali metals (K‐mirro). The results obtained showed that anion‐radicals initiate the polymerization predominantly via addition to the monomer and the pure alkali metals by proton transfer from the monomer to the initiator. The active centers of propagation in these systems were most probably of an alcoholate type in spite of the difficulties for direct proof of their nature.
Silyl enol ethers as monomer. II. Radical copolymerizations of α‐trimethylsilyloxystyrene with electron‐accepting monomers and acid‐catalyzed desilylation of the resulting copolymers
Authors: Nagai Katsutoshi , Chiba Keiji , Asada Keisuke , Masui Keikichi , Kuramoto Noriyuki 
Published: April 2003

AbstractRadical copolymerizations of α‐trimethylsilyloxystyrene (TMSST), a silyl enol ether of acetophenone, with electron‐accepting monomers such as maleic anhydride (MA) and fumaronitrile (FN) were investigated. TMSST underwent alternating copolymerizations with both MA and FN irrespective of the feed composition, whereas it failed to copolymerize with diethyl fumarate (DEF). The alternating copolymers of TMSST with MA and FN were desilylated with concentrated hydrochloric acid as a catalyst to form polymers containing γ‐lactone rings. The formation of the lactone rings was also observed in the desilylation of an alternating copolymer of TMSST with acrylonitrile (AN) under the similar conditions.
Thermoset resins containing sterically hindered alkyne groups for reduced crosslink density
Authors: Unroe Marilyn R. , Reinhardt Bruce A. 
Published: April 2003

AbstractA series of thermoset matrix materials with phenylethynyl and phenoxyphenylethynyl end groups were prepared to assess the extent of crosslinking in the cured resins by thermoanalytical and thermomechanical methods. These novel materials with varying flexibility and thermal stability of both the end group and backbone were evaluated against a group of materials known to contain a substantial number of primary acetylenic thermal crosslinking sites. The evaluation indicated increased thermooxidative stability of the secondary acetylenic materials over the primary acetylenic systems at or below 600°F (312°C). However, above 600°F, the secondary systems were less thermooxidatively stable than the primary structures due to the thermal decomposition of the phenyl pendants near 400–450°C (750–842°F). Cure exotherms for the monomers exhibited typical Gaussian behavior with discernable cure onsets and maxima. Cure maxima for the secondary acetylene quinoxalines were close to their thermal decomposition temperature (450°C). Percentages of weight retained varied from 64 to 92% after isothermal aging at 600°F for 200 h in circulating air. Glass transition temperatures of the secondary systems more closely approximated the values calculated for linear homopolymers of similar structure. The increased linearity of the cured secondary systems is further verified by fracture analysis which indicated a 20% increase over the room temperature value of the observed KQ for its comparable primary system analog.
Synthesis and the preliminary analysis of block copolymers of 3,3′‐bis(azidomethyl)‐oxetane and 3‐nitratomethyl‐3′‐methyloxetane
Authors: Talukder Mostafa A. H. , Lindsay Geoffrey A. 
Published: April 2003

AbstractThe preparation of poly[3,3′‐bis(azidomethyl)oxetane‐b‐3‐nitratomethyl‐3′‐methyloxetane‐b‐3,3′‐bis(azidomethyl)oxetane], BAMO–NMMO–BAMO triblock copolymer, was attempted by using p‐bis(α,α‐dimethylchloromethyl)benzene (p‐DCC) with silver hexafluoroantimonate (AgSbF6) to initiate the sequential polymerization of NMMO and BAMO. The analysis of the polymer by different techniques such as nuclear magnetic resonance (NMR), infrared (IR) spectroscopy, and differential scanning calorimetry (DSC) show that the structure of the polymer is composed of a two‐phase domain structure of amorphous NMMO phases and crystalline BAMO phase. The molecular weight distribution of the polymer, determined by gel permeation chromatography‐low angle laser light scattering (GPC‐LALLS) was fairly narrow which indicates that the chains could be propagating by a quasi‐living ionic mechanism. Thermogravimetric analysis (TGA) shows that the decomposition temperature of the polymer is about 204°C, which indicates good thermal stability of the polymer.
Polyamideimides containing carbonyl and ether connecting groups
Authors: Havens S. J. , Hergenrother P. M. 
Published: April 2003

AbstractPolyamideimides were prepared from the reaction of trimellitic anhydride chloride with seven diamines containing carbonyl and ether groups between the aromatic rings. Several of these polyamideimides were semicrystalline as evidenced by wide angle x‐ray diffraction and differential scanning calorimetry. Glass transition temperatures ranged between 187 and 245°C and crystalline transition temperatures ranged between 317 and 416°C. A series of copolyamideimides from a mixture of 1,3‐bis(4‐aminophenoxy‐4′‐benzoyl) benzene and 1,4‐bis(4‐aminophenoxy‐4′‐benzoyl) benzene were similarly prepared. These copolyamideimides were semicrystalline and formed tough, solvent resistant films with good tensile properties.
Polymerization photoinitiated by carbonyl compounds. IX. Methyl methacrylate polymerization photoinitiated by anthraquinone in presence of triethylamine
Authors: Encinas M. V. , Majmud C. , Lissi E. A. 
Published: April 2003

AbstractAddition of triethylamine (TEA) notably increases the efficiency of anthraquinone (AQ) as photoinitiator of methyl methacrylate (MMA) free radical polymerization in nonpolar solvents. On the other hand, when alcohols or acetonitrile are employed as solvents the addition of TEA decreases the AQ photoinitiated polymerization rate. The polymerization efficiency measured in nonpolar solvents decreases when the MMA concentration increases. These results are explained in terms of quenching of the AQ‐TEA charge transfer complex by MMA. This conclusion is supported by the decrease in AQ photoconsumption and AQH2 formation produced by the monomer addition.
Polymeric oxidizing reagents based on polyacrylamides: Effect of the nature and extent of crosslinking on reactivity
Authors: George Benny K. , Pillai V. N. Rajasekharan 
Published: April 2003

AbstractAcrylamide was copolymerized with N,N′‐methylene‐bis‐acrylamide (NNMBA), tetraethyl‐eneglycol diacrylate (TEGDA), and divinyl benzene (DVB) in different proportions to afford crosslinked polyacrylamides with varying nature and extent of crosslinking. These insoluble polymers were functionalized with the N‐bromoamide function and the reactivity of the resulting polymeric N‐bromoamide was investigated under different conditions. The capacities of the reagents varied from 6.7 mequiv / g for the linear polymeric reagent to 1.1 mequiv / g for the 15% DVB‐crosslinked reagent. Oxidation of benzoin to benzil was used as the model reaction. Investigation of the reaction under different conditions of solvent and varying molar excess revealed a significant influence of the nature and extent of crosslinking in deciding the extent of reaction. In the case of NNMBA‐crosslinked reagents, the reactivity increased up to 10% crosslinking and then decreased. The reactivity of the reagents increased up to 15% crosslinking in the case of TEGDA‐crosslinked ones and for DVB‐crosslinked reagents the reactivity decreased with crosslinking. The polarity of the crosslinking agent and its molar percentage on the polymeric reagent (crosslink density) are factors affecting the solvent compatibility, which in turn, is decisive in the facilitation of the reactions.
Solution polymerization of methyl methacrylate using trioctylmethylammonium persulfate initiator: Kinetics of polymerization and activation parameters for the primary decomposition of the initiator
Authors: Gupta G. N. , Mandal B. M. 
Published: April 2003

AbstractThe kinetics of solution polymerization of methyl methacrylate using trioctylmethylammonium persulfate (aliquat persulfate) at 60°C has been studied in t‐butyl alcohol, N,N‐dimethyl formamide, acetonitrile, dioxane, acetone, and methyl ethyl ketone. The rate of polymerization depends markedly on the solvent used. The initiator exponent is close to 0.5 in the first three solvents but larger than this value in the other three solvents. The overall activation energy of the polymerization has been determined in all the solvents. The rate constants and activation parameters for the primary decomposition of the initiator have been determined in the first three solvents where ideal polymerization conditions prevail. The activation parameters for the decomposition of AQ2S2O8 in the organic solvents depend on the type of solvent. They are very different from those of the free S2O2−8 ion in water. These differences have been explained taking into consideration the various ionic forms in which the initiator exists in the studied solvents using a previously postulated model of the activated state.
13C‐NMR study of crosslinking and long‐chain branching in linear polyethylene induced by 60Co gamma ray irradiation at different temperatures
Authors: Zhu Qingren , Horil Fumitaka , Kitamaru Ryozo , Yamaoka Hitoshi 
Published: April 2003

AbstractH‐type crosslinking and Y‐type long‐chain branching have been examined for linear polyethylene samples irradiate at different temperatures with 60Co gamma rays in vacuum by solution‐state 13C‐NMR spectroscopy. In this study, relatively low molecular weight samples were irradiated with doses less than a gel dose in both solid and molten states. Resonance lines associated with H‐links and Y‐branches have clearly been observed for each irradiated sample and their radiation yields significantly depend on the irradiation temperature and the morphology of the samples. In particular, the G‐value for the production of Y‐branches is higher than that for H‐links at lower temperatures, while the latter is superior to the former at higher temperatures. This may be due to the decrease in the concentration of the primary radicals, which are formed by main‐chain scissions and associated with the production of Y‐branches, by the recombination with small fragments at higher temperatures. The radiation yields of methyl branches and double bonds are also briefly discussed.
Fluorinated poly(ether sulfone)s
Authors: Feiring Andrew E. , Wonchoba Edward R. , Arthur Samuel D. 
Published: April 2003

AbstractNew fluorinated poly(ether sulfone)s were prepared from bisphenols and α,ωbis(4‐fluorophenylsulfonyl)perfluoroalkanes. The fluorinated sulfone monomers were synthesized by reaction of 4‐fluorobenzenethiol salts with perfluoroalkylene diiodides, followed by oxidation. Sodium carbonate mediated polymerization gave high molecular weight polymers in excellent yield. The polymers are generally soluble in chlorinated hydrocarbons and some dipolar solvents, are amorphous with Tg's in the range of 120–160°C and are stable to 400°C. They form clear, colorless films by solution casting. Cast films have dielectric constants and dissipation factors somewhat below those of typical poly(ether sulfone)s, and show good permeability and selectivity for O2/N2 gas separations.
Anionic polymerization of acrylates. I. Polymerization of 2‐ethylhexylacrylate in nonpolar solvents
Authors: Vlčcek Petr 
Published: April 2003

AbstractInitiation with a combined initiator n‐butyllithium/lithium tert‐butoxide in the ratio 1:6 brings the anionic polymerization of 2‐ethylhexylacrylate (EtHA) in toluene and n‐heptane at temperatures between −78 and −20°C up to a quantitative conversion. In the initial stages of the process the molecular weight distribution (MWD) of the products is polymodal as a result of the stablizing function of the alkoxide; MWD of the final product after a complete consumption of the monomer is medium, being visibly dependent on the reaction temperature and without any distinct content of low‐molecular weight components, which suggests a sufficient activity of all growth centers, and thus an essential restriction of side termination reactions.
Lifetime of living polymers in cationic polymerization. III. Living polymerization of isobutyl vinyl ether initiated by a cationogen/etalcl2 system in the presence of 1,4‐dioxane as an added base
Authors: Choi Won Ok , Sawamoto Mitsuo , Higashimura Toshinobu 
Published: April 2003

AbstractThe concentration ([P*]) and lifetime (half‐life) of the propagating species were measured in the living cationic polymerization of isobutyl vinyl either initiated by the 1‐(isobutoxy) ethyl acetate [CH3COOCH (OiBu) CH3]/ethylaluminum dichloride (EtAlCl2) system in the presence of excess 1,4‐dioxane in n‐hexane at 0 to +70°C; the acetate serves as a cationogen that forms an initiating vinyl ether‐type carbocation. The measurements were based on the end‐capping reaction with sodiomalonic ester [Na⊕⊖CH (COOEt)2], which was shown to react rapidly and quantitatively with the living growing end. From the terminal malonate group of the quenched polymers, [P*] was determined by 1H‐NMR spectroscopy. In contrast to its constancy during the polymerization, [P*] progressively decreased with time after the complete consumption of monomer. The postpolymerization decay was first order in [P*], and the lifetime (half‐life) of the living end was determined from the decay rate constant. The lifetime increased on lowering polymerization temperature, decreasing EtAlCl2 concentration, and increasing dioxane concentration. In particular, the “base‐stabilized” living ends, generated by the CH3COOCH (OiBu) CH3/EtAlCl2/dioxane system, turned out extremely stable at 0°C (half‐life > 5 days in the absence of monomer).
Synthesis and characterization of new photosensitive poly (oxyaryleneoxydisilane)s from 1,2‐bis (diethylamino) tetramethyldisilane and various bisphenols
Authors: Padmanaban Munirathina , Kakimoto Masa‐Aki , Imai Yoshio 
Published: April 2003

AbstractA new class of polymers containing a photosensitive disilane unit in the polymer main chain with inherent viscosities between 0.1 and 0.59 dL/g was prepared by the melt polycondensation of 1,2‐bis (diethylamino) tetramethyldisilane and various bisphenols. The polymers were characterized by UV, IR, 1H‐NMR, and elemental analysis. Poly(oxyaryleneoxydisilane)s were soluble in a variety of common organic solvents and have a wide range of glass transition temperatures varying between −65 and 135°C, depending on the arylene structure. Most of the polymers were stable up to 350°C in both air and nitrogen atmospheres. The inherent viscosity of the polymer containing the 1,6‐napthalene unit decreased drastically upon UV light irradiation, indicating its photodegradation.
Redox behavior of pyridinium salts and their polymers having radical stabilizing groups
Authors: Kitamura Naoya , Nambu Yoko , Endo Takeshi 
Published: April 2003

AbstractThe redox behavior of pyridinium salts having various substituents capable of stabilizing pyridinyl radicals at the 4‐position was investigated by cyclic voltammetry in water with a platinum electrode, and their redox potentials were more positive in the order of 4‐substituents of acetyl > cyano > carbomethoxy > carbamide groups. Sodium dithionite was found to be suitable for a chemical reducing agent of the pyridinium salts. Two types of homopolymers with pendant 4‐carbamido‐pyridinium groups were prepared and their redox potentials were more positive than the corresponding model compounds. The positive shift might be caused by charge repulsion between the neighboring pyridinium cations on the polymer main chain in the oxidized state.
Radical copolymerization of 2‐ethylacrylic acid and methacrylic acid
Authors: You Hong , Tirrell David A. 
Published: April 2003

AbstractCopolymers of 2‐ethylacrylic acid (EAA) and methacrylic acid (MAA) were prepared in bulk and in N,N‐dimethylformamide (DMF). Although precipitation of the copolymers was observed in bulk, the reaction mixtures remained apparently homogeneous in DMF. Best‐fit terminal‐model reactivity ratios were determined by a nonlinear least squares technique to be rMAA = 1.14 and rEAA = 0.23 in bulk, and rMAA = 1.91 and rEAA = 0.09 in 50% DMF solution. Examination of 13C‐NMR spectra provided convincing evidence for the formation of statistical copolymers. Copolymerizations richer in MAA provided copolymers of higher molecular weights.
Kinetic study of the cationic photopolymerization of epoxy monomers
Authors: Decker C. , Moussa K. 
Published: April 2003

AbstractThe photoinitiated cationic polymerization of di‐epoxy monomers has been studied using real‐time infrared (RTIR) spectroscopy. The polymerization rate and the amount of unreacted monomer were determined directly from the conversion vs. time curves recorded. The cure speed was greatly increased by using a Kr+ laser (337.4 nm) as radiation source. A 0.25 s exposure proved sufficient to make react more than 60% of the epoxy groups. The overall polymerization quantum yield was evaluated to be 200 mol photon‐1. Dark polymerization was shown to develop extensively after the UV exposure for about 30 min and may represent up to 80% of the total process. The hardening of the UV‐cured tack‐free coating was found to occur mainly in the dark, leading after 1 h to a very hard and glassy material. A bimolecular chain termination process is postulated to account for the decay profile of the reactive species observed after UV exposure.