bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rigid rod molecules as liquid crystal thermosets. I. Rigid rod amides
Authors: Hoyt Andrea E. , Benicewicz Brian C. 
Published: April 2003

AbstractA series of rigid rod amide monomers based on 2,2′‐disubstituted‐4,4′‐diaminobiphenyl were prepared and characterized by DSC and hot stage polarized light microscopy. The monomers were endcapped with maleimide, nadimide, and methylnadimide functionalities. With one exception, all of the materials could be thermally polymerized. Nematic liquid crystalline behavior was observed in three of the new materials which could be crosslinked in either the nematic or isotropic phase. Fast heating rates with hot stage polarized light microscopy were necessary to determine the melting and phase behavior before substantial crosslinking occurred during the heating process. One of the methylnadimide endcapped monomers also showed lyotropic liquid crystalline behavior.
Phenylquinoxaline–Aryl ester block copolymers
Authors: Labadie Jeff W. , Hedrick James L. 
Published: April 2003

AbstractPhenylquinoxaline–aryl ester block copolymers were synthesized using well‐defined phenolic hydroxyl terminated oligomers via a monomers/oligomer approach. Phenylquinoxaline oligomers with molecular weights of 5600 and 12,900 g/mol were prepared from the condensation of 1,4‐bis(phenylglyoxalyl)benzene and 3,3′‐diaminobenzidine in the presence of 4‐hydroxylbenzil. The oligomers were copolymerized with isophthaloyl chloride and bisphenol A in tetrachloroethane to afford the desired phenylquinoxaline–aryl ester block copolymers. Copolymers with polyester compositions ranging from 15–50 wt % were prepared by controlling the monomers/oligomer stoichiometry. The majority of the materials displayed single phase morphologies with Tgs intermediate to the Tgs for the poly (phenylquinoxaline) and polyester homopolymers. Plots of the reciprocal of the Tg of the copolymers versus composition agreed well with values predicted by the Fox equation. A multiphase morphology was obtained for the copolymer with the highest polyester block length (⋍ 13,000 g/mol), which displayed a Tg at 190 and 300°C indicative of a glassy–glassy system. Significant improvement in the elongations were observed for the copolymers relative to the poly(phenylquinoxaline) homopolymer. The improved elongations were obtained with minimal sacrifice to the modulus. These materials represent the first example of poly(phenylquinoxaline) block copolymers from well‐defined phenylquinoxaline oligomers.
Evidence for long chain branching in polyethyloxazoline
Authors: Warakomski John M. , Thill Bruce P. 
Published: April 2003

AbstractIt has been reported that in the polymerization of 2‐alkyl‐2‐oxazolines extensive chain transfer to monomer occurs with subsequent repolymerization and the formation of branched polymer. We undertook a study to determine if polyethyloxazoline is branched. The approach was hydrolysis of the polymer followed by reacylation; characterization at each step was by size exclusion chromatography, viscometry, and NMR spectroscopy. In addition, ethyl oxazoline was polymerized to low and high conversion and characterized. We conclude that polyethyloxazoline does contain hydrolytically unstable linkages which are probably branches formed late in the polymerization.
Molecular location in a nonaqueous lyotropic liquid crystal polymer
Authors: Friberg Stig E. , Yu Bing , Campbell Gregory A. 
Published: April 2003

AbstractA surfactant bis[2‐(10‐undecenoyloxycarbonyl)ethyl] (p‐vinylbenzoyl) methylammonium chloride formed a lamellar liquid crystal in native form and retained the structure after polymerization. Addition of heptadiene, of glycerylmonomethacrylate, and of both to the surfactant monomer gave an isotropic solution, which was transformed to a lamellar liquid crystal after polymerization. Low angle X‐ray diffractometry was used to determine the interlayer spacing and to estimate the location of the added molecules. 1.6‐Heptadiene was located between methyl group layers of the surfactant chains with 46 vol % of the molecules penetrating between the hydrocarbon chains of the surfactant. Addition of both the polar and the nonpolar monomer followed by polymerization caused the latter to be expelled from the space in between the chains.
Studies on the thermotropic liquid crystalline polymer. I. Synthesis and properties of polyamide‐azomethine‐ether
Authors: Li Chien‐Hui , Chang Teh‐Chou 
Published: April 2003

AbstractA series of polyamide‐azomethine‐ethers was prepared by condensation of 4,4′‐diaminoanilide with 4,4′‐diformyl‐α,ω‐diphenoxyalkane, 4,4′‐diformyl‐3,3′‐methoxy‐α,ω‐diphenoxyalkane, and 4,4′‐diformyl‐3,3′‐ethoxy‐α,ω‐diphenoxyalkane, respectively. The inherent viscosities of polymers were obviously increased when the polymers were treated by heat under nitrogen at 220°C. The thermotropic liquid crystalline properties were examined by DSC, microscope observations, and TGA. All of the polymers, except polymer A‐1, exhibit thermotropic liquid crystalline properties. They also exhibit threaded and/or Schlieren textures examined by the polarizing microscope which indicate a nematic phase. In most cases, the mesophase exists up to ca. 400‐460°C shown by TGA study. The mesophase cannot exist above 400‐460°C because of the thermal decomposition.
Polyurethane elastomers with hydrolytic and thermooxidative stability. II. Polyurethanes with n‐alkylated polyurethane soft blocks
Authors: Chapman Toby M. , Benrashid Ramazan 
Published: April 2003

AbstractBlock copolyurethanes with N‐alkylated polyurethanes as nonself‐associating soft segments are prepared. The polymers compare well in hydrolytic stability with block copoly(N‐alkylamide urethane)s prepared in an earlier study but have better dimensional stability on exposure to moist heat. They show comparable hydrolytic stability and better oxidative stability than a poly(ether urethane) from the earlier study. The effect of different alkyl substituents on tensile properties and thermostability is studied. The tensile properties are also examined as a function of soft‐segment molecular weight at constant weight‐percent of hard‐block. It is shown that yield stress and ultimate stress increase and elongations decrease as the soft‐block M̄n increases. DSC measurements do not generally show well defined endotherms with few exceptions but dynamic mechanical testing of some samples does show transitions between 14 and 23°C.
Studies of alkylthio‐substituted aromatic diamines as curatives for polyurethane cast elastomers
Authors: Davis Robert L. , Nalepa Christopher J. 
Published: April 2003

AbstractA series of alkylthio‐substituted aromatic diamines was synthesized using a convenient high yield procedure. The method consisted of heating a mixture of dialkyl disulfide and aromatic diamine in the presence of cuprous iodide or other Lewis acid catalyst. Dialkyl disulfide was continually replenished as consumed, throughout the reaction, to maintain the desired reaction temperature. Compounds so prepared were isolated by first precipitating the catalyst with solid caustic and then vacuum flashing the crude products. When desired, the final product purity could be increased by washing with acid to remove starting material or reaction intermediates. The final products were often liquids or low melting solids and showed utility as curatives for polyurethane cast elastomers. Alkylthio substitution of the aromatic diamines lowered reactivity toward isocyanates and generally provided for facile processing during molding. The series of derivatives allowed for great flexibility in controlling both diamine reactivity and the physical properties of the final elastomers. These benefits arose from the diverse electronic, steric and isomeric properties of the derivatives. Polymers were prepared from the alkylthio‐substituted compounds and commercially available TDI‐based prepolymers using conventional cast elastomer techniques. The physical properties of the polymers were determined and their relation to alkylthiodiamine structure examined.
Living carbocationic polymerization of p‐halostyrenes. III. Syntheses and characterization of novel thermoplastic elastomers of isobutylene and p‐chlorostyrene
Authors: Kennedy J. P. , Kurian Joseph 
Published: April 2003

AbstractNovel linear and three‐arm star radial thermoplastic elastomers (TPE) comprising rubbery polyisobutylene (PIB) center blocks connected to glassy poly(p‐chlorostyrene) (PpClSt) outer blocks have been synthesized by sequential monomer addition. For triblock polymer synthesis isobutylene (IB) was added continuously to a bifunctional initiating system (dicumylmethyl ether/TiCl4) dissolved in CH3Cl/methylcyclohexane solvent mixture at –80°C. After the living PIB sequence has reached the desired molecular weight p‐chlorostyrene (pClSt) was added to produce the PpClSt end blocks. The synthesis conditions for the TPEs were developed with the help of model experiments using the 2‐chloro‐2,4,4‐trimethylpentane (TMPCl)/TiCl4 initiating system and subsequent PIB‐PpClSt diblock syntheses. The triblock and radiol block polymers after solvent extraction exhibited excellent TPE characteristics. Copolymer compositions were determined by 1H‐NMR and UV spectroscopy and further characterization was carried out by GPC, DSC, DMTA, and selective solvent extraction techniques. The TPEs exhibit two Tg's characteristic of glassy PpClSt (129°C) and rubbery PIB (−70°C) segments. Cast TPE films were clear and gave tensile strengths of 1.2‐21 MPa with elongations of 460–1500%. Transmission electron microscopy (TEM) of a triblock polymer containing ca. 38 wt % PpClSt suggests cylindrical PpClSt domains of 40–70 nm length and 25–35 nm diam embedded in a PIB matrix.
Polyurethane‐polyacrylamide IPNs. I. Synthesis and characterization
Authors: Nair Prabha D. , Jayabalan M. , Krishnamurthy V. N. 
Published: April 2003

AbstractHydrophobic‐hydrophilic interpenetrating polymer networks (IPNs) of polyurethane and polyacrylamide have been synthesized. The IPNs have been characterized by IR, thermal, and mechanical studies. SEM studies indicate phase mixing of some IPNs. Solvent resistance and surface hydrophilicity as evidenced by contact angle measurements suggest that these IPNs could be used for biomedical applications.
Liquid crystal polymers containing macroheterocyclic ligands. III. Side chain liquid crystalline polymethacrylates containing mesogenic units based on diarylacetylenes and benzo‐15‐crown‐5
Authors: Percec V. , Rodenhouse R. 
Published: April 2003

AbstractThe synthesis and polymerization of 4′‐[4‐ethynyl‐1‐(11‐methacryloylundecan‐1‐yloxy) benzene] benzo‐15‐crown‐5 (8), 4′‐[4‐ethynyl‐4′‐(11‐methacryloylundecan‐1‐yloxy) biphenyl] benzo‐15‐crown‐5 (15), 4′‐[2‐ethynyl‐6‐(11‐methacryloylundecan‐1‐yloxy) naphthalene] benzo‐15‐crown‐5 (24), and 4′‐[2‐ethynyl‐6‐(11‐methacryloylundecan‐1‐yloxy)naphthalene]‐5′‐ethylbenzo‐15‐crown‐5 (35) is described. The synthesis and characterization of 4′‐[4‐(4‐ethynyl‐1‐(2‐ethynyl‐6‐(6‐hydroxyhexan‐1‐yloxy)naphthathalene)benzene]) benzo‐15‐crown‐5 (29) is also presented. Both monomers and polymers were characterized for their mesomorphic behavior. 8, poly(8), and 15 are crystalline. Due to the insolubility of 15, poly(15) could not be synthesized. 24 is crystalline, while poly(24) displays a monotropic nematic mesophase. 29 exhibits also a monotropic nematic mesophase. 35 is crystalline, while poly(35) displays an enantiotropic nematic mesophase which is kinetically controlled due to its close proximity to the glass transition temperature.
Copolymers of 2‐vinyl‐4,4‐dimethylazlactone with styrene and ethyl α‐hydroxymethylacrylate
Authors: Muthiah Jeno , Mathias Lon J. 
Published: April 2003

AbstractThe monomer reactivity ratios for copolymerization of 2‐vinyl‐4,4‐dimethylazlactone (VA) and ethyl α‐hydroxymethylacrylate (EHMA) were 0.20–0.24 and 0.53–0.74, respectively, which show that EHMA is slightly more reactive with VA than with itself and should lead to random copolymers favoring alternation. The VA–styrene (VA–St) system also has a tendency to form random copolymers but with increased tendency for alternation with both r1 and r2 between 0.18–0.22. Tg's of VA–EHMA and VA–St copolymers varied between 100 and 136°C, and 96 and 117°C, respectively. Thermolysis of VA–EHMA copolymers resulted in crosslinking via the ring‐opening reaction of VA groups by EHMA alcohols, followed by transesterification involving EHMA units at higher temperatures leading to highly crosslinked structures. The performed dimer of EHMA and VA was also synthesized and found to be an effective crosslinking agent in free radical vinyl polymerizations.
Synthesis and characterization of new soluble aromatic polyimides from 3,4‐bis (4‐aminophenyl)‐2,5‐diphenylfuran and aromatic tetracarboxylic dianhydrides
Authors: Jeong Hwa‐Jin , Oishi Yoshiyuki , Kakimoto Masa‐Aki , Imai Yoshio 
Published: April 2003

AbstractNew soluble polyimides with inherent viscosities of 0.2–0.6 dL/g were synthesized from 3,4‐bis (4‐aminophenyl)‐2,5‐diphenylfuran and various aromatic tetracarboxylic dianhydrides by the conventional two‐step method which involved ring‐opening polyaddition and subsequent cyclodehydration. Almost all of the polymides were generally soluble in a wide range of organic solvents such as N,N‐dimethylacetamide, 1,3‐dimethyl‐2‐imidazolidone, m‐cresol, o‐chlorophenol, and pyridine. The polyimide prepared from pyromellitic dianhydride was crystalline, whereas the other polyimides were amorphous. All the polyimides have glass transition temperatures in the range of 281–344°C and showed no appreciable weight loss up to 410°C in both air and nitrogen atmospheres.
Infrared spectral study of noncrystalline rodlike polymers
Authors: Gaudiana R. A. , Sinta R. F. 
Published: April 2003

AbstractOriented and unoriented films of noncrystalline, wholly‐aromatic, rodlike polyamides, and polyesteramides were examined by infrared spectroscopy. The results indicate that orientation, accomplished by means of mechanical stretching, approaches 80% in both polymer classes. Examination of the NH and the CO stretching region revealed an increase in the population of nonhydrogen bonded species (plateauing at ∼ 85%) as orientation increases. This unusual result may be caused by interchain steric interactions which may also be responsible for both the noncrystalline morphology and the non‐lyotropic behavior exhibited by these polymers.
Synthesis and electroconductivities of poly(2‐methoxy‐5‐methythio‐1,4‐phenylene vinylene) and copolymers
Authors: Jin Jung‐Il , Park Chi‐Kyun , Shim Hong‐Ku 
Published: April 2003

AbstractPoly(2‐methoxy‐5‐methylthio‐1,4‐phenylene vinylene), PMTPV, and copolymers containing both unsubstituted or 2,5‐dimethoxy‐substituted and 2‐methoxy‐5‐methylthio‐1,4‐phenylene vinylene units were prepared in thin films from their water‐soluble, sulfonium salt precursor polymers. Doping of drawn and undrawn films of PMTPV with I2 vapor led to conductivities of 10−4–10−3 S cm−1, which is significantly lower than those reported for poly(2,5‐dimethoxy‐1,4‐phenylene vinylene). Conductivity of I2‐doped copolymer films ranges from 10−3–100 S cm−1 depending on composition.
A model of the kinetics of macrocyclic BPA carbonate formation
Authors: Kosky P. G. 
Published: April 2003

AbstractCyclic oligocarbonates are synthesized by two‐phase interfacial reactions of aryl bischloroformates in the presence of an amine phase transfer catalyst and an alkali: nClOCOArOCOCl + 4nNaOH → (OArOCO)n + 2nNaCl + nNa2CO3 + 2nH2O. The organocarbonate product may be a macrocyclic oligomer or a linear chain polymer. A qualitative mechanism for this behavior has been proposed by Brunelle, Boden, and co‐workers. Four steps are identifiable: activation of the aryl bischloroformate by the amine catalyst, hydrolysis of a portion of this intermediate at the aqueous/organic phase interface, oligomerization between activated and hydrolyzed moieties also at the interface, and chain terminating carbamate formation that leads to polymer. An important modification is made within the framework of the Brunelle and Boden mechanism. While the intramolecular cyclization reaction is formally second‐order overall, it behaves as a first‐order process. The kinetic constants for both this pseudo‐first‐order cyclization step and the corresponding second‐order linearization step are simply related. It is speculated that the above relationship can be generalized for a whole class of pseudo‐first‐ and second‐order rate constants for similar macrocyclic reactions.
Amorphous celluloses stable in aqueous media: Regeneration from SO2–amine solvent systems
Authors: Isogai A. , Atalla R. H. 
Published: April 2003

AbstractAmorphous celluloses were prepared by regeneration of cellulose from its solutions in the SO2–diethylamine–dimethylsulfoxide (SO2–DEA–DMSO) solvent system, and other selected SO2–amine–organic solvents. The celluloses were amorphous whether regenerated in water or in alcohols or other organic solvents; in this respect the observations differ from all prior experience in the regeneration of cellulose. These celluloses retain their amorphous character even after extended soaking in water at room temperature. Viscosity measurements have shown that little or no depolymerization occurs during the dissolution, regeneration, and drying processes. Thus the procedures allow the preparation of amorphous celluloses of a wide range of molecular weights for use to model the behavior of amorphous domains in fibrous celluloses. The unusual stability of the amorphous cellulose structures prepared by these procedures is attributed to very rapid decomposition of the SO2–amine complex with the cellulosic hydroxyl groups which is believed to occur in the solvated state. The rate of decomposition of this complex appears to be sufficiently high so that the cellulose chains aggregate in an amorphous state before they have any opportunity to realign into crystalline domains.
Synthesis and characterization of silicon‐containing polyamides from aromatic sulfone ether diamines and aromatic organosilicon diacid chlorides
Authors: Jadhav A. S. , Maldar N. N. , Shinde B. M. , Vernekar S. P. 
Published: April 2003

AbstractNew polymides and copolyamides containing silicon and sulfone ether linkages, soluble in common aprotic solvents and having inherent viscosities of 0.3–0.6 dL/g have been synthesized by solution condensation of bis‐(4‐chlorocarbonyl phenyl) dimethylsilance (DMSC) and/or bis‐(4‐chlorocarbonyl phenyl) diphenylsilance (DPSC) with 4,4′‐[sulfonylbis‐(4,1‐phenylenoxy)] bisbenzenamine, 3,3′‐[sulfonylbis (4,1‐phenyleneoxy)] bisbenzenamine, and bis (4‐aminophenyl) ether. These polymers were characterized by infrared spectra, solution viscosity, thermooxidative degradation, differential scanning calorimetry, and x‐ray diffraction. These polymers show good thermal stability.
Cinnamate ester containing liquid crystalline side chain polymers
Authors: Whitcombe M. J. , Gilbert A. , Hirai A. , Mitchell G. R. 
Published: April 2003

AbstractThe synthesis of methacrylate esters of 4‐cyanophenyl‐(4‐(ω‐hydroxyalkyloxy)) cinnamates, with spacer lengths of 2 and 6 methylene units and the synthesis of the corresponding acrylate ester with a spacer of 2 methylene units are described. The methacrylate monomers were polymerized by free radical polymerization, both as homopolymers and as copolymers with the analogous benzoate monomer of spacer length 6. The acrylate ester could not be polymerized successfully under the same reaction conditions. Polymers were characterized by NMR spectroscopy, gel permeation chromatography, differential scanning calorimetry, and thermo‐optic observations. Of the monomers prepared, only the cinnamate with a hexamethylene spacer shows a mesophase, seen on supercooling of the melt. All of the polymers prepared were liquid crystalline, with smectic behavior predominating in the polymethacrylates with the longer spacer group. A narrow nematic region is seen just below the clearing temperature with a range of 3–9°C, nematic character is increased in the copolymer series with the degree of incorporation of the cinnamate monomer with the spacer group of length 2.
Polymerization of vinyl monomers initiated by KO2–charge transfer agent systems. II
Authors: Han Yang‐Kyoo , Kim Ji‐Heung , Choi Sam‐Kwon 
Published: April 2003

AbstractVinyl monomers having electron acceptor groups such as nitroethylene, acrylonitrile, and acrolein were polymerized by KO2–charge transfer agent initiator systems in dimethylsulfoxide (DMSO) at 25°C. The new initiator systems were found to be stable for almost 1 month under nitrogen atmosphere. The initial rate of polymerization was so fast that both conversion and molecular weight of the polymers obtained were high. Especially their molecular weight distribution was observed to be very narrow by means of gel permeation chromatography (GPC). The anion radicals generated by one electron transfer from potassium superoxide (KO2) to charge transfer agents such as naphthalene, benzoquinone, azobenzene, etc., were suitable as initiator for the anionic polymerization of electron acceptor monomers. Study on block copolymerization of nitroethylene with acrylonitrile or acrolein was also attempted.
Selective degradation of silicone copolymers and networks
Authors: Keohan F. L. , Swint S. A. , Buese M. A. 
Published: April 2003

AbstractAn exhaustive end‐capping method for the analysis of silicone copolymers and networks using hexamethyldisiloxane in the presence of trifluoromethanesulfonic acid was demonstrated. The hard block of a polymide‐co‐polysiloxane was isolated by the equilibration of the copolymer with a large excess of hexamethyldisiloxane and subsequently examined by size exclusion chromatography. Addition cured polyimidesiloxane networks were also equilibrated with an excess of the disiloxane and the resulting oligmoers characterized by gas chromatography of the end‐capped fragments.
Molecular engineering of liquid crystal polymers by living polymerization. II. Living cationic polymerization of 11‐[(4‐cyano‐4′‐biphenyl) oxy] undecanyl vinyl ether and the mesomorphic behavior of the resulting polymers
Authors: Percec V. , Lee M. , Jonsson H. 
Published: April 2003

AbstractThe synthesis and living cationic polymerization of 11‐[(4‐cyano‐4′‐biphenyl)oxy]‐undecanyl vinyl ether (6–11) are described. The mesomorphic phase behavior of poly(6–11) with different degrees of polymerization was compared to that of 6–11 and of 11‐[(4‐cyano‐4′‐biphenyl) oxy] undecanyl ethyl ether (8–11) which is the model compound of the monomeric structural unit of poly(6–11). 6–11 displays a monotropic SA and a monotropic nematic mesophase while 8–11 an enantiotropic SA mesophase. Poly(6–11) with low degrees of polymerization exhibits an enantiotropic SA mesophase. Poly(6–8) with high degrees of polymerization displays an enantiotropic SX (i. e., an unidentified smectic phase) and an enantiotropic SC mesophase. These results demonstrate that the transformation of the nematic mesophase of the monomer into a smectic mesophase after polymerization, occurs at the level of monomeric structural unit.
Polychloromethylstyrene microspheres: Synthesis and characterization
Authors: Margel Shlomo , Nov Eliahu , Fisher Inna 
Published: April 2003

AbstractThe synthesis and characterization of polychloromethylstyrene microspheres are described. The effect of various factors, e.g., monomer concentration, surfactant concentration, solvents, crosslinker, etc., on the yield, diameter, and size distribution of these microspheres was elucidated. Conditions to covalently bind various primary amino ligands to these microspheres in aqueous solution were also established. The possible routes to modify the surface of these microspheres to obtain functional groups other than chloromethyl are discussed.