bluuebunny/crossref_metadata_2025_split huggingface dataset:
IR studies of polyimides. I. Effects of chemical and physical changes during cure
Authors: Pryde C. A. 
Published: April 2003

AbstractA detailed study has been made of the thermal cure of two polyimides using infrared analysis. It is shown that two of the IR bands commonly used to determine the amount of imidization are affected by both interference from other species and by polymer morphology. These bands, located near 1780 cm−1 and 730 cm−1, overlap bands attributed to anhydride, which is formed when the polymer is heated. A correction for this effect is described. However, the measured absorbances of these bands are also subject to a dichroic effect. Any anisotropy in the samples can therefore affect the results. A third band, that located near 1370 cm−1, does not overlap anhydride peaks and did not, using the approach described here, display any effect due to dichroism. Thus it appears to offer a reliable way of following imidization by IR.
Studies of the polymerization of diallyl compounds. XLI. Discussion of substantially identical gel points among three isomeric diallyl phthalates
Authors: Matsumoto Akira , Ogasawara Yuji , Nishikawa Sadahiko , Aso Takayuki , Oiwa Masayoshi 
Published: April 2003

AbstractIn the bulk polymerization of three isomeric diallyl phthalates, diallyl phthalate (DAP), diallyl isophthalate, and diallyl terephthalate (DAT), no difference in the actual gel point was substantially observed. This interesting gelation behavior is discussed in terms of the correlation between gelation and the difference in cyclization modes, and the difference in reactivity between the uncyclized and cyclized radicals for crosslinking; the nonconsecutive addition in DAT polymerization led to a delayed gelation and the cyclized radical in DAP polymerization showed an enhanced reactivity for crosslinking.
Preparation of poly(ethylene terephthalate) in the presence of a telechelic perfluoropolyether
Authors: Pilati F. , Bonora V. , Manaresi P. , Munari A. , Toselli M. , Re A. , De Giorgi M. 
Published: April 2003

AbstractPolyethylene terephthalate (PETP) has been prepared from dimethyl terephthalate and ethylene glycol in the presence of various amounts of a telechelic fluorinated macromer with methyl ester end‐groups using Ti(OBu)4 as the catalyst. The final products are heterophasic with a perfluoropolyether phase embedded in a PETP matrix. The effects of the fluorinated polymer on the reaction rates in the first and second stages of the reaction and on some properties (Tg, Tm, and contact angle) are discussed.
Synthesis and characterization of liquid crystalline polymethacrylates, polyacrylates, and polysiloxanes containing 4‐methoxy‐4′‐hydroxy‐α‐methylstilbene‐based mesogenic groups
Authors: Percec Virgil , Tomazos Dimitris 
Published: April 2003

AbstractThe synthesis and characterization of polymethacrylates and polyacrylates containing 4‐methoxy‐4′‐hydroxy‐α‐methylstilbene side groups attached either directly or through flexible spacers containing eleven, eight, six, three, and respectively two methylenic units, and of the polysiloxanes containing the same mesogenic group connected through flexible spacers containing eleven, eight, six, and respectively three methylenic units are described. All polymers exhibit thermotropic liquid crystallinity. The nature of the mesophase is determined by the spacer length. However, the nature of the polymer backbone determines the thermal stability of the mesophase. That is, for the same spacer length and similar polymer molecular weight, the most flexible polymer backbone leads to the highest isotropization temperature.
A study of sulfur‐free thiuram vulcanization using differential scanning calorimeter
Authors: Duchác̆ek Vratislav , Bhattacharyya Timir Baran , Kuta Antonin 
Published: April 2003

AbstractA number of curative mixtures without rubber and with natural rubber or polybutadiene based on binary and tertiary combinations of zinc oxide, tetramethylthiuram disulfide, and 2‐mercaptobenzothiazole were treated in a differential scanning calorimeter. From the shapes of exothermal curves a zinc‐accelerator complex formation has been examined. Although the experimental results can give no direct evidence for the structure of the complexes, they do contribute to an elucidation of the complex formation in the vulcanization process.
Polyimides containing carbonyl and ether connecting groups. II
Authors: Hergenrother P. M. , Havens S. J. 
Published: April 2003

AbstractIn a continuation of our effort on polyimides containing carbonyl and ether connecting groups between aromatic rings, several new polyimides were prepared and characterized. A few of these polymers were semi‐crystalline. Glass transition temperatures ranged from 164 to 258°C and crystalline melt temperatures were observed between 350 and 424°C. The semi‐crystalline polyimide from the reaction of 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride and 1,3‐bis(4‐aminophenoxy‐4′‐benzoyl)benzene provided transparent orange films with excellent tensile properties, exceptional resistance to solvents and strong base, and high thermooxidative stability. In addition, this polyimide provided excellent adhesive strength for joining titanium (6A1–4V) to titanium.
Kinetic modelling and optimization of the trifluoropropylmethylsiloxane polymerization
Authors: Veith C. A. , Cohen R. E. 
Published: April 2003

AbstractUse of promoter dimethylsulfoxide (DMSO) in conjunction with initiator normal butyllithium has resulted in rapid and controllable ring‐opening polymerization of 1,3,5‐tris‐(3′,3′,3′‐trifluoro‐propyl)1,3,5‐trimethylcyclotrisiloxane at 40°C; monomer consumption rate can be varied by at least four orders of magnitude depending on the ratio of promoter‐to‐initiator concentrations. Compared to the sodium counterion also studied here, the lithium initiator slows the backbiting alkyl‐reactions which cause degradation of polymer to cyclics containing four or more fluoroal‐kylsiloxy units. This previously uninvestigated polymerization methodology offers greater opportunity for capturing high, nonequilibrium polymer yield of this fluoroalkylsiloxane through appropriately timed termination of the reaction. To facilitate this optimization, a kinetic model of the polymerization was developed by solving the isothermal, constant density rate expressions for a two‐step, series mechanism. The solution to the coupled system of nonhomogeneous ordinary differential equations is obtained by matrix variation of parameters. The rate constants were determined by appropriate kinetic analysis of the experimental data obtained for polymer and cyclics concentrations as a function of time under various conditions. This results in a quantitative model capable of predicting optimum polymerization time to maximize the yield of poly(3,3,3‐trifluoropropylmethylsiloxane) at ca. 85–90%.
On the kinetics and mechanism of copolymerization of vinyl acetate and itaconic monomers
Authors: Kotzeva L. , Mateva R. 
Published: April 2003

AbstractThe introduction of anionic hydrophylic groups in the pendant chain of polyvinyl alcohol improves its surface and adhesive properties. For the purpose of synthesizing raw materials for preparation of modified polyvinyl alcohol with enhanced performance characteristics, the copolymerization of vinyl acetate with itaconic acid and diethyl itaconate at concentrations up to 9 mol % in methanol solution using azo‐bis‐isobutyronitrile and tert‐butylcyclohexylperoxydicarbonate as initiators has been studied. The experiments were performed using two different methods of addition of the itaconic monomer—single, at the beginning of the process, and continuous. It was established that the process rate decreases as the quantity of the second comonomer increases. The reaction order in terms of itaconic acid ( −2, 95) and reactivity ratios for both pairs vinyl acetate and itacinic acid (r1 = 0.053 and r2 = 31) and vinyl acetate and diethyl itaconate (r1 = 0.125 and r2 = 18) were determined. The products obtained were characterized by IR and NMR. It was confirmed that for the case of single addition at the beginning of the process a two‐phase system is formed while the continuous addition resulted in random group distribution.
Metallocene–methylaluminoxane catalysts for olefin polymerizations. III. Reduction of η5‐cyclopentadienyl trichlorides of titanium and zirconium
Authors: Bueschges Ulrich , Chien James C. W. 
Published: April 2003

AbstractThe reactions occurring between the components of metallocene and methylaluminoxane (MAO) catalyst leading to the reduction of the former were studied by electron paramagnetic resonance (EPR). At low Al/Zr ratios, CpZrCl3 (Cp = η5‐cyclopentadienyl) was reduced to simple trivalent Zr species (g = 1.998, a(91Zr) = 12.3 G) without other superhyperfine splittings. At higher Al/Zr ratios the reactions proceed further to form two CpZr(III) hydrides (g = 1.991, a(H) = 5.5 G; and g = 2.00, a(H) = 3 G). Two CpTi(III) hydrides were also produced by the reaction of MAO with CpTiCl3 (g = 1.989, a(H) = 7.4 G, a(Ti) = 8 G; and, g = 1.995, a(H) = 4.5 G, a(Ti) = 8 G). In the case of Cp*TiCl3 (Cp* = η5‐pentamethyl cyclopentadienyl) initially a multitude of paramagnetic species were formed. After long reaction time the final products show EPR features consistent with two η3: η4‐(1,2,3‐trimethyl‐4,5‐dimethylene cyclopentadienyl)hydrido Ti(III) species: the abundant one with g = 1.999, (H, sextet) = 9.5 G, a(Ti) = 9.5 G, and a weaker one of g = 1.975, a(H) = 4.8 G. All the five protons of these species and as well as those in the Cp hydrido complexes of Ti and Zr undergo facile HD exchanges with D2. MAO is important in the formation of these hydrides because they are not formed by trimethyl aluminum reduction. The presence of tetrahydrofuran suppresses the hydride formation. The possible structures for the hydrido species and reactions producing them are discussed.
Copolymerization of methyl acrylate and vinyl acetate catalyzed by ethylaluminium chlorides
Authors: Florjańczyk Zbigniew , Skórkiewicz Bogdan 
Published: April 2003

AbstractThe copolymerization of vinyl acetate with methyl acrylate in the presence of Et2AlCl, Et1.5AlCl1.5, and Et2AlCl‐benzoyl peroxide systems has been investigated. The influence of monomer ratios and organoaluminium compound concentration on the copolymer yield and composition have been determined and discussed. The monomer sequences distribution has been studied by means of 13C‐NMR. It was found that organoaluminium compounds in the studied systems catalyze not only the alternating copolymerization, but also the homopropagation of both monomers. An alternating copolymer was obtained in reactions carried out at −78°C, when a large excess of vinyl acetate was used in the monomer feed.
Radiolysis of poly(acetaldehyde‐co‐chloral): A positive E‐beam resist
Authors: Zhao X. , Xu B. , Chien James C. W. , Khanna D. N. 
Published: April 2003

AbstractAcetaldehyde and chloral were copolymerized using triethyl aluminum catalyst. The copolymer (ACC) obtained with equimolar monomer feed is not alternating in structure as it was once thought to be; it is comprised of two fractions differing in MW and composition. ACC has good thermal stability which is further improved by endcapping. Radiolysis in vacuo caused depolymerization with a G(M) value (number of monomers produced per 100 eV) of about 4000 to 80% completion. The G(S) value for chain scission is 1.9. These processes are effectively inhibited by benzoquinone. Oxygen markedly increases G(M) to ca. 18,000 and > 97% completion. Addition of tetrabutyl ammonium salt or tetramethyl urea has no effect on the depolymerization, whereas the addition of di‐t‐butyl‐p‐cresol causes an induction period after which normal unzipping ensues. Even UV photolysis of ACC in the presence of oxygen produces monomer with a quantum yield of 1.7, but very little photolysis occurs in the absence of oxygen. Gamma radiolysis sensitized by (C6H5)2IPF6 has G(M) value of 32,700. These results are very similar to the radiolysis and photolysis of the homopolymer of monochloroacetaldehyde and reinforce the mechanisms proposed for them. The E‐beam sensitivity of ACC is about 3 × 10−6 C cm−2.
Surface modification of polymers. II. Grafting with glycidyl acrylates and the reactions of the grafted surfaces with amines
Authors: Allmér K. , Hult A. , Rånby B. 
Published: April 2003

AbstractThe surface of low density polyethylene has been grafted with glycidyl acrylate and glycidyl methacrylate by photoinitiation. ESCA measurements on the grafted surface showed a 72% coverage for glycidyl acrylate and 52% for glycidyl methacrylate after 10 min of grafting with UV irradiation. ATR–IR showed a 10 times more extensive grafting for glycidyl acrylate than for glycidyl methacrylate after 10 min of grafting, indicating reaction to deeper layers. Acetone and ethanol were used as solvents: acetone yielded slightly more grafting at the surface. The grafted surfaces were reacted with 2M solutions of aniline and propylamine in ethanol. After 4 h reaction at 60°C, with aniline 52% of the epoxy groups while for propylamine 96% of the groups were consumed, as measured with ATR–IR.
Synthesis of poly(amino acid)s on molecular assemblies formed by functional active esters of amino acids
Authors: Hanabusa K. , Tsutsumi H. , Kurose A. , Shirai H. , Hayakawa T. , Hojo N. 
Published: April 2003

AbstractThe new active β‐alanine and glycine esters (6 and 7) of N‐hydroxy‐2,3‐dihexadecylsuccinimide were prepared and their polycondensation was studied. The aggregation behavior of these esters was examined by an electron microscopy and an osmotic method. They formed multilamella in water and reversed micelle in nonpolar solvents. These solvents were found to be suitable for the polycondensation, which gave the corresponding poly(amino acid)s. The results of polycondensation can be explained by assuming that the aggregations, that is, multilamella in water and reversed micelle in nonpolar solvents, are playing an important role in the polycondensation.
Grafting of a bicycloorthoester onto polymers bearing sulfonium salt structures
Authors: Uno Hitomi , Takata Toshikazu , Endo Takeshi 
Published: April 2003

AbstractGraft copolymerization of a bicycloorthoester (BOE) with polymer‐supported sulfonium salts was studied. Several polymer‐supported sulfonium salts were prepared by the homopolymerizations of p‐vinylbenzyl tetramethylenesulfonium hexafluoroantimonate (2) and 4‐(p‐vinylphenyl)butyl tetramethylenesulfonium hexafluoroantimonate (3), and by the copolymerizations of 2 with some vinyl monomers (n‐butyl vinyl ether, styrene, acrylonitrile, and p‐styrenesulfonic acid potassium salt). These sulfonium salts could initiate the polymerization of BOE to give grafted polymers. Temperature dependences of the catalytic activity of them were not so dramatic as that of benzyl tetramethylenesulfonium hexafluoroantimonate (1), but the activities of them were higher than that of 1 at temperatures lower than 80°C. The conversion of BOE in the polymerizations with these polymer initiators was ca. 30–70% at 120°C for 7 h. An effect of the comonomer structure on the catalytic activity was observed and styrene was the best comonomer for 2 in terms of the reactivity of the copolymer. The spacer‐modified sulfonium salt (homopolymer of 3) was slightly lower than polymer‐supported benzyl type sulfonium salt (homopolymer of 2) in the catalytic activity.
Polymerization of methyl methacrylate with cupric laurate–benzoin system as initiator
Authors: Pal Prabir Kumar , Nandi Dipa , Chaudhuri Ajit Kumar 
Published: April 2003

AbstractThe polymerization of methyl methacrylate initiated by cupric laurate in combination with benzoin has been investigated in carbon tetrachloride medium at 60°C. The rate of polymerization was found to be proportional to the square root of both cupric ion and benzoin concentrations, and to the 1.5th power of the monomer concentration. Spectral studies indicated that there is a complex formation between cupric ion and the monomer methyl methacrylate. A reaction scheme, based on initial formation of the complex and its subsequent reaction with benzoin to produce the free radicals responsible for initiation has been postulated to explain the observed results.
Preparation and complexation of an A–B–A type triblock copolymer consisting of helical poly(L‐proline) and random‐coil poly(ethylene oxide)
Authors: Jeon Seung Ho , Park Soon Moon , Ree Taikyue 
Published: April 2003

AbstractBy using L‐proline N‐carboxyanhydride (LPNCA) and amino‐group terminated poly(ethylene oxide) (ATPEO), an A–B–A–type [A = poly(L‐proline) (PLP), B = poly(ethylene oxide) (PEO)] triblock copolymer (POP) was prepared which is water‐soluble. In the POP, A = PLP is helical, and B = PEO is random coil. From the observations of the NMR spectra, specific optical rotation, and x‐ray diffraction of the POP, it was found that the PLP component of the POP exists nearly as Form II PLP with trans‐configuration, and interferes the crystal growth of PEO component, in solid state. With the addition of PMAA into an aqueous POP solution, dramatic decreases of reduced viscosity and pH are observed until the unit‐mole‐concentration‐ratio (UMCR) [PMAA]/[POP] reaches its value of unity, while a distinct increase in turbidity appears. This shows a 1 : 1 interpolymer complex formation between PMAA and POP in aqueous medium through hydrogen bonding. The curves of viscosity, pH, and turbidity versus UMCR [PMAA]/[POP] show breaks at [PMAA]/[POP] = 0.3, suggesting the selective complexation of PLP component (ca. 30 unit‐mol %) of POP with PMAA. The x‐ray diffraction curve of the complex POP/PMAA shows entirely no diffraction patterns, indicating that the ordered POP structure (mainly due to that of PLP component) is completely destroyed owing to the complexation between POP and PMAA.
γ‐irradiation of polypropylene in vacuum and in air
Authors: Imai Masahiko , Xu Lu Gong , Ametani Kazuo , Tutiya Mituaki 
Published: April 2003

AbstractPolypropylene films were irradiated with 60Co γ‐rays in vacuum or in air and stored in air. Just after irradiation, the concentration of carbonyl group of the sample irradiated in air only increased with dose. The concentrations of both samples increased with storage time. The more the absorbed doses, the higher the increasing rates. The increasing rate of the concentration of carbonyl group during irradiation in air was higher than those during storage in air. Just after irradiation, the tensile strengths and the elongations of the both samples somewhat increased with dose at the doses less than 5 Mrad, but decreased at doses more than 13 Mrad. The tensile strength and the elongation of the sample irradiated in air decreased with storage time. Those of the sample irradiated in vacuum also decreased with storage time but the decreasing rates were much smaller than those in the sample irradiated in air. The gel fractions of the samples irradiated in vacuum and annealed in vacuum were somewhat higher than those irradiated in vacuum and not annealed. To elucidate high oxidation rate in the sample irradiated in air during and after irradiation, reaction mechanisms were discussed. To clarify the difference of mechanical properties between the samples irradiated in vacuum and in air, the effect of crosslink was considered, together with the oxidation.
Radical ring‐opening polymerization behavior of vinylcyclopropanes derived from dienes and chloroform
Authors: Endo Takeshi , Suga Katsufumi 
Published: April 2003

Abstract1,1‐Dichloro‐2‐vinylcyclopropane (Ia), 1,1‐dichloro‐2‐methyl‐2‐vinylcyclopropane (Ib), 1,1,2‐trichloro‐2‐vinylcyclopropane (Ic) were prepared from the corresponding dienes and chloroform in the presence of a phase transfer catalyst (PTC), R4N+Cl−. Monomers Ia–Ic underwent a clean 1,5‐type radical ring‐opening process to afford the corresponding polymers in good yield. Further, the relative rate of polymerization and reaction of (I) with thiophenol were studied.
Electrochemical synthesis of conducting polymers from oligomers containing thiophene and furan rings
Authors: Galal Ahmed , Lewis Edmund T. , Ataman O. Yavuz , Zimmer Hans , Mark Harry B. 
Published: April 2003

AbstractOligomers containing 2,5‐thienylene and 2,5‐furanylene units were synthesized by NiCl2 (dppp) (dppp = Ph2PCH2CH2CH2PPh2) coupling of Grignard compounds with the appropriate bromothiophene or bromofuran; UV and electrochemical data are given and discussed in terms of number and kind of heterolene units in the oligomeric species.
Surface and solution properties of polysiloxane–poly(methyl methacrylate) graft copolymer
Authors: Chujo Yoshiki , Samukawa Hiroshi , Yamashita Yuya 
Published: April 2003

AbstractA polysiloxane–poly(methyl methacrylate) (PMMA) graft copolymer was prepared by hydrosilylation reaction between a SiH containing polysiloxane and an allyl‐terminated PMMA. The obtained graft copolymer was blended with PMMA homopolymer. The addition of only 0.01 wt % of graft copolymer was sufficient to make PMMA surfaces hydrophobic. In acetone–cyclohexane mixed solvent, the graft copolymer formed a polymeric micelle by the aggregation of PMMA branches.
Preparation of monodisperse hydrophilic polyamide by anionic polymerization of bicyclic oxalactam
Authors: Hashimoto Kazuhiko , Sumitomo Hiroshi , Washio Atsuko 
Published: April 2003

AbstractThe preparation of a monodisperse hydrophilic polyamide was achieved in the anionic polymerization of a bicyclic oxalactam, 8‐oxa‐6‐azabicyclo[3.2.1]octan‐7‐one (abbreviated BOL) with the use of N‐benzoyl BOL and potassium pyrrolidonate (2 and 0.5 mol % to BOL, respectively) in dimethyl sulfoxide at 25°C. The number‐average molecular weight of the polyamide increased in direct proportion to the monomer conversion, and was consistent with the value calculated from the amounts of the consumed monomer and activator. The molecular weight distribution (MWD) of the polyamide obtained until the middle stage of polymerization (polymerization time, < 10 min; monomer conversion, < 60%) was found to be narrow (Mw/Mn = 1.1). The MWD was gradually broadened in the later stage of the polymerization, which may result from the redistribution of molecular weight of the resulting polyamide not only by the polymerization–depolymerization equilibrium, but also by transamidation between polymer chains.
Hydrolysis of alkyl cyanoacrylate and ethoxycarbonylpropenoylphosphonate polymers
Authors: Cooper A. W. , Harris P. J. , Kumar G. K. , Tebby J. C. 
Published: April 2003

AbstractThe polymers of ethyl α‐cyanopropenoate (widely known as cyanoacrylate) and dimethyl (α‐ethoxycarbonyl)propenoylphosphonate have been hydrolyzed and their rates of degradation to formaldehyde have been compared. The phosphate polymer produced much less formaldehyde than the cyanopropenoate polymer as required for an improved surgical adhesive. In a comparative study, the rate of aqueous hydrolysis of a high molecular weight cyanoacrylate polymer differed from a previous report. The nature and the hydrolytic properties of the end groups in the two types of polymer are discussed.
Synthesis of aromatic dicarboxyl‐terminated poly(methyl methacrylate) macromonomers
Authors: Chujo Yoshiki , Kobayashi Hisaaki , Yamashita Yuya 
Published: April 2003

AbstractHydroxyl‐ or amino‐terminated prepolymers were prepared by radical polymerization of methyl methacrylate in the presence of 2‐mercaptoethanol or 2‐aminoethanethiol hydrochloride, respectively, as a chain transfer agent. The resulting prepolymers were subjected to react with trimellitic anhydride to form aromatic dicarboxyl‐terminated poly(methyl methacrylate)s. These condensation‐type macromonomers and terephthalic acid were condensed with bisphenol‐A to produce polyester–poly(methyl methacrylate) graft copolymers.