bluuebunny/crossref_metadata_2025_split huggingface dataset:
Well‐defined side‐chain liquid‐crystalline polysiloxanes
Authors: Hempenius Mark A. , Lammertink Rob G. H. , Vancso G. Julius 
Published: April 2003

AbstractA route to well‐defined side‐chain liquid‐crystalline polysiloxanes (ratio of weight‐to number‐average molar masses M̄w/M̄n < 1.2 is reported. Anionic ring‐opening polymerization of pentamethylvinylcyclotrisiloxane yielded a poly(dimethylsiloxane‐co‐methylvinylsiloxane) backbone. A flexible disiloxane spacer was used to connect 4‐(ω‐alkenyloxy)‐4′‐cyanobiphenyl mesogenic molecules to the vinyl groups which belong to the backbone, leading to a side‐chain liquid‐crystalline polysiloxane (SCLCP) which has its mesogens distributed regularly along the main chain. Preliminary measurements indicate an electro‐optic switching time τs = 1 min at 20°C and 7 s at 32°C (dc, 5 V/μm)).
A deuteron NMR study on order and phase behaviour of liquid‐crystalline copolymers
Authors: Martin Andreas , Tefehne Christoph , Gronski Wolfram 
Published: April 2003

AbstractLiquid‐crystalline (LC) block copolymers of lamellar morphology were prepared via anionic polymerization of polystyrene‐block‐1,2‐polybutadiene and subsequent introduction of a deuterated mesogen by polymer analogous reaction. Deuteron NMR measurements show that the first‐order nematic/isotropic transition in the block copolymer is changed to a critical behaviour under the influence of shear. In the nematic phase the order parameter is reduced with respect to the homopolymer, and there is no evidence of an isotropic boundary layer of the LC‐block at the nematic/isotropic interface.
Syndiotactic‐specific polymerization of propene with a Ni‐based catalyst
Authors: Pellecchia Claudio , Zambelli Adolfo 
Published: April 2003

AbstractPolymerization of propene at −78°C in the presence of a homogeneous catalytic system based on a Ni(II) diimine derivative and methylaluminoxane affords prevailingly syndiotactic crystalline poly(propylene) (rr triad content ≈80%). 13C NMR analysis of the polymer microstructure indicates that the stereochemistry of the monomer insertion is controlled by the configuration of the methine carbon of the growing chain end (unlike‐1,3 asymmetric induction). This is the first example of stereospecific homopolymerization of propene promoted by a late transition metal catalyst.
Polymerization of o‐quinodimethanes, 1. Radical polymerization of 1‐methoxy‐o‐quinodimethane formed in situ by thermal isomerization of 1‐methoxy‐benzocyclobutene
Authors: Chino Keisuke , Takata Toshikazu , Endo Takeshi 
Published: April 2003

AbstractThe first radical polymerization of 1‐methoxy‐o‐quinodimethane (2) generated by thermal ring‐opening isomerization of 1‐methoxybenzocyclobutene (1) is described. The polymerization of 1 in the presence of a radical initiator afforded an MeOH‐insoluble polymer (3) in moderate yield at temperatures above 90°C. The structure of the obtained polymer is consistent with a ring‐opening polymerization. The yield of the polymer increased with the amount of initiator. Radical copolymerization with methyl acrylate was carried out. Treatment of 3 with acid gave poly(o‐phenylenevinylene), quantitatively.
Rate constants for the reaction of hydrated electrons and hydroxyl radicals with acrylate monomers
Authors: Bíró Ággnes , Takács Erzsébet , Wojnárovits Laszlo 
Published: April 2003

AbstractThe hydrated electron (e−aq) and hydroxyl radical rate constants with 18 acrylate‐, methacrylate‐, crotonate‐, fumarate‐ and maleate esters are discussed. The constants approach the diffusion‐controlled limit. k(e−aq) and k(OH) change in opposite direction; if k(e−aq) is high then k(OH) is small. This tendency is connected with the nucleophilic character of e−aq and the electrophilic character of OH, although the site of attack of e−aq and OH is different: carbonyl versus vinyl group.
Ring‐opening polymerization of cyclic urethanes and ring‐closing depolymerization of the respective polyurethanes
Authors: Neffgen Stephan , Keul Helmut , Höcker Hartwig 
Published: April 2003

AbstractThe cationic ring‐opening polymerization of trimethylene urethane (tetrahydro‐2 H‐1,3‐oxazin‐2‐one) in the melt with methyl trifluoromethanesulfonate as initiator results in poly(trimethylene urethane) in yields of ≈70%. Under the same reaction conditions 2,2‐dimethyltrimethylene urethane (5,5‐dimethyltetrahydro‐2H‐1,3‐oxazin‐2‐one) cannot be polymerized. Poly(2,2‐dimethyltrimethylene urethane), however, was obtained via polycondensation polymerization. Both polymers exhibit a uniform microstructure as deduced from NMR spectroscopic analysis. Ring‐closing depolymerization in the melt with dibutyltin dimethoxide or titanium tetraisopropoxide at 140°C results the respective monomers in yields of ≈90%.
Thermoreversible gelation of isotactic poly(methyl methacrylate) in butyl acetate: a differential scanning calorimetry study
Authors: Spěváček Jiří , Saiani Alberto , Guenet Jean‐Michel 
Published: April 2003

AbstractThe thermal behaviour of thermoreversible gels prepared well below room temperature from isotactic poly(methyl methacrylate) (i‐PMMA) in butyl acetate (BAC) was investigated by means of differential scanning calorimetry. Gel‐formation and gel‐melting enthalpies together with melting enthalpy of the solvent were determined as functions of polymer concentration. The results are consistent with the existence of a polymer/solvent complex with a stoichiometry of 1,5–2 BAC molecules per i‐PMMA monomeric unit.
Synthesis of vinyl ether‐capped telechelic poly(tetrahydrofuran)
Authors: Hashimoto Tamotsu , Furukawa Tomohiro , Kodaira Toshiyuki 
Published: April 2003

AbstractVinyl ether‐terminated telechelic poly(tetrahydrofuran) (poly(THF)) was synthesized by the reaction of a bifunctional living cationic polymer of THF with an excess of Na⊕⊖OCH2CH2OCHCH2 in THF at 0°C. The obtained polymer has narrow molecular weight distribution and end functionality close to two.
Hysteresis in the glucose permeability versus pH characteristic for a responsive hydrogel membrane
Authors: Baker John P. , Siegel Ronald A. 
Published: April 2003

AbstractA side‐by‐side diffusion cell was used to study the permeability of glucose through a temperature‐ and pH‐sensitive poly(N‐isopropylacrylamide‐co‐methacrylic acid) hydrogel membrane. At fixed temperature (37°C), lowering pH in one side of the cell induced hydrogel volume collapse and strongly attenuated glucose permeation across the membrane. Hysteresis was observed in the glucose permeability versus pH characteristic.
The use of photoinitiated free‐radical cyclopolymerization in the preparation of novel side‐chain liquid‐crystalline polydienes
Authors: Hall Alan William , Lacey David , Buxton Peter Ian 
Published: April 2003

AbstractThe technique of photoinitiated free‐radical cyclopolymerization has been used to produce a variety of novel side‐chain liquid‐crystalline (SCLC) polymers in which an alicyclic ring structure is incorporated into a polymer backbone. Most of the SCLC polymers gave glass transition temperatures (Tg) around room temperature and clearing points around 60–70°C. However, the poly(1,5‐hexadiene) was the exception to this, exhibiting a Tg value of 14.5°C and a clearing point of 132.5°C. Confirmation of the structure of the alicyclic ring along the polymer backbone is extremely difficult to obtain, but evidence is given in the paper to support the ring structure.
Miscibility of semirigid thermotropic liquid crystalline polycarbonate with poly(vinyl chloride)
Authors: Sato Moriyuki , Ujiie Seiji 
Published: April 2003

AbstractMiscibility and morphology of polymer blends of semirigid thermotropic liquid crystalline (LC) polycarbonate (LCPC) with three commercial amorphous poly(vinyl chloride)s (PVC) having various molecular weights were investigated by means of differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). No phase separation was observed in the LCPC/PVC polymer blends. LCPC forms miscible polymer blends with the PVCs independent of molecular weight. The dynamic storage modulus of the LCPC/PVC polymer blends changes systematically with blend composition.
Phase equilibria in polymer/solvent systems, 8. Swelling of chemically crosslinked polymers in mesogenic substances in different states
Authors: Frahn Stephanie , Borchard Werner 
Published: April 2003

AbstractSwelling curves of chain end‐linked polyurethane networks in mesogenic swelling agents were determined gravimetrically. Different slopes of the swelling curves are observed above and below the transition temperature of the liquid‐crystalline to the isotropic state. From the sign of the slope it can be derived that the swelling agent is not in the liquid‐like state in the gel if the pure swelling agent is liquid‐crystalline.
Dielectric and dynamic mechanical relaxation of poly(ether ether ketone)/poly(etherimide) blends below the glass transition
Authors: Goodwin Andy , Marsh Robert 
Published: April 2003

AbstractDielectric relaxation spectroscopy (DRS) and dynamic mechanical thermal analysis (DMTA) were used to investigate the secondary relaxation behaviour of poly(ether ether ketone) (PEEK), poly(etherimide) (PEI) and a miscible PEEK/PEI blend. The data from each technique, for the γ‐process, did not lie on the same Arrhenius line, while the rate of molecular motion of the γ‐process in the blends was largely an average of each component's motions. The β‐process in PEI was plasticised by the presence of PEEK.
Gel synthesis by transesterification of glycol‐modified poly(N‐isopropylacrylamide) with O,O‐diethyl dithiophosphate
Authors: Bromberg Lev 
Published: April 2003

AbstractSynthesis of poly(N‐isopropylacrylamide‐co‐2‐hydroxyethyl methacrylate‐co‐ethylene glycol dimethacrylate) gels containing pendant mercapto groups via transesterification of 2‐hydroxyethyl methacrylate moieties with O,O‐diethyl dithiophosphate is described and the gel structure elucidated by 1H and 31P NMR and elemental analysis. The gels respond to changes in their liquid environment.
Thermally switchable polyrotaxane as a model of stimuli‐responsive supramolecules for nano‐scale devices
Authors: Fujita Hiroaki , Ooya Tooru , Kurisawa Motoichi , Mori Hideharu , Terano Minoru , Yui Nobuhiko 
Published: April 2003

AbstractA polyrotaxane consisting of many β‐cyclodextrins (β‐CDs) and a triblock copolymer of poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG) capped with bulky end‐groups was synthesized as a model of stimuli‐responsive supramolecules for nanoscale devices. The polyrotaxane was reversibly soluble‐insoluble in water in response to temperature. This was achieved through the assembled and dispersed states of β‐CDs along the block copolymer. It is considered that intermolecular hydrogen bondings of β‐CDs, as well as the PEG segment length of the copoloymer, are predominant factors for regulating such thermally switchable behavior of the polyrotaxane.
Functionalization of polypropylene by grafting with itaconic acid
Authors: Yazdani‐Pedram Mehrdad , Vega Héctor , Quijada Raúl 
Published: April 2003

AbstractGrafting of polypropylene was carried out in both boiling xylene and decalin as solvent medium with itaconic acid (2‐methylenesuccinic acid) as functional polar monomer using 2,5‐dimethyl‐2,5‐bis(tert‐butylperoxy)hexane (Lupersol 101) as radical initiator. It was found that the temperature influenced the percentage of monomer grafted onto polypropylene and that the amount of monomer incorporated was practically constant after 5 min. The results also show that the amount of monomer incorporated is proportional to the initial monomer concentration used in the grafting reaction, although for higher initiator concentrations a reduction in the percentage of grafting was found.
Synthesis and photo‐crosslinking of oriented side‐chain liquid crystalline polymers
Authors: Kawatsuki Nobuhiro , Takatsuka Hirohumi , Yamamoto Tohei , Sangen Osamu 
Published: April 2003

AbstractNew photo‐crosslinkable side‐chain liquid‐crystalline methacrylate polymers comprising m‐[4′‐(n‐cinnamoyloxyalkoxy)biphenyl‐4‐yloxy]alkyl groups (m, n = 2, 6) were synthesized. All polymers exhibit a nematic liquid‐crystalline phase depending on the spacer length (5a–5d). Aligned thin films could be obtained using a rubbed polyimide‐coated substrate, and they could be photo‐crosslinked without change in the aligned structure. The photo‐crosslinked film of 5d (m = n = 6) showed a stable alignment up to 300°C.
Polymeric mesoions, 3. Synthesis of polymeric mesoionic 1,3‐diazinium‐olates via polymer analogous modification of a polythiourea from m‐phenylenediamine and p‐phenylene diisothiocyanate
Authors: Deutschmann Thomas , Ritter Helmut 
Published: April 2003

AbstractMesoionic poly(1,1′‐(1,3‐phenylene)‐3,3′‐(1,4‐phenylene)‐bis(5‐decyl‐2‐decylthio‐4,6‐dioxo‐1,3‐diazine)) (6) was prepared by cyclisation of the isothiourea component of poly(1,1′‐(1,3‐phenylene)‐3,3′‐(1,4‐phenylene)‐bis(2‐decylisothiourea)) (4) with decylmalonic acid (5) by use of dicyclohexylcarbodiimide (DCC). Polymer 4 was obtained by polymer analogous alkylation of poly(1,1′‐(1,3‐phenylene)‐3,3′‐(1,4‐phenylene)‐bisthiourea) (3). For comparison of spectroscopic data, 5‐butyl‐2‐propylthio‐4,6‐dioxo‐1,3‐diphenyl‐1,3‐diazine (9) was synthesized as low molecular weight model compound.
Piezoelectricity of mechanically oriented S‐elastomers
Authors: Eckert Tobias , Finkelmann Heino , Keck Mario , Lehmann Walter , Kremer Friedrich 
Published: April 2003

AbstractFerroelectricity and thus piezoelectricity are well known features of low molar mass chiral smectic C (Sc*) liquid crystals. We present a new technique to orientate macroscopically the director as well as the smectic layers of a Sc*‐polymer network by applying a suitable mechanical field. The uniform orientation of the network film is checked by X‐ray diffraction. According to the phase symmetry electromechanical measurements indicate the existence of a polar axis of the network and the direct as well as the inverse piezoelectric effect is demonstrated.
Investigation of metal clusters dispersed in styrene‐co‐(ethyl methacrylate) copolymers by means of high resolution transmission electron microscopy
Authors: T. Galo Cárdenas , C. Elizabeth Salgado , L. Viviana Vera , Yacamán Miguel J. 
Published: April 2003

AbstractStyrene/ethyl methacrylate (SEMA) colloids were obtained by cocondensation at 77 K of the monomers with several metals such as Au, Pd, In and Sn. The colloids were polymerized with 2,2′‐azoisobutyronitrile and dibenzoyl peroxide as radical initiators at 60°C for 3.5 h. A viscosity average molecular weight (104 < Mv < 105) was obtained depending upon the metal used. The particle size of these clusters dispersed in the copolymers ranges from 20 to 31 Å. The metal clusters are incorporated in the copolymers.
Unsymmetric 1,4‐naphthylene‐containing polysulfones
Authors: Douglas Judy E. , Wang Zhi Yuan 
Published: April 2003

AbstractThe design and synthesis of a new unsymmetric monomer, 1‐chloro‐4‐(4‐fluorobenzenesulfonyl)naphthalene (1), was accomplished and polymerized with several bisphenols. Three of these polymers represent the successful incorporation of a bulky 1,4‐naphthylene unit into the commercially known polysulfones, Udel, Radel R and Victrex. All unsymmetric polysulfones obtained were determined to be amorphous and displayed glass transition temperatures in the range of 218–288°C. The gas permeability suffered while the permselectivity was marginally improved with naphthyl insertion into Udel.
Microemulsions with polymerizable surfactants. γ‐ray induced copolymerization of styrene and 11‐(acryloyloxy)undecyl(trimethyl)ammonium bromide in three‐component cationic microemulsion
Authors: Dreja Michael , Tieke Bernd 
Published: April 2003

AbstractStyrene and the cationic surfactant 11‐(acryloyloxy)undecyl(trimethyl)ammonium bromide (AUTMAB) form transparent, globular microemulsions in water without any addition of a cosurfactant. Upon γ‐irradiation, the two monomers copolymerize at room temperature and form nanolatex particles of about 21 nm in diameter consisting of a copolymer with a mole ratio of styrene to surfactant of approximately 1.5:1. Excess surfactant is polymerized in the micellar solution by formation of homopolymer. A structure model is presented taking into account that the surfactant most likely forms the particle shell. Due to the polar, covalently bonded shell the polymer particles can be easily redispersed.
Experimental discrimination between competing nucleation theories in microemulsion polymerizations
Authors: Kim Dong Ryul , Napper Donald H. 
Published: April 2003

AbstractThe particle nucleation processes involved in the microemulsion polymerizations of styrene and methyl methacrylate have been investigated using pyrene fluorescence intensity measurements as a function of conversion. Very distinctive differences were observed between the results for the two different monomers. The styrene fluorescence results were consistent with nucleation occurring within the microemulsion droplets, followed by the subsequent heterocoagulation of the nucleated particles with remaining droplets. The very different methyl methacrylate data were consistent with a homogeneous nucleation mechanism.
A facile synthesis of polyamides from aromatic diisocyanates and dicarboxylic acid catalyzed by Lewis acids
Authors: Wei Yen , Jia Xinru , Jin Danliang , Davis Franklin A. , Starner William E. 
Published: April 2003

AbstractAromatic polyamides were prepared by an AlCl3 or HCl‐catalyzed polymerization of toluene diisocyanate or methylenebis(phenyl isocyanate) with adipic acid at low temperatures (≤100°C) in a short reaction time (3–4 h). The intrinsic viscosity of the polymers was approximately 1.1 dL/g as determined at 25°C with m‐cresol as solvent, indicating that the polyamides obtained by this method have relatively high molecular weights. The polymers exhibit high glass transition temperatures and good thermal stability.
On the crystallization of γ‐isotactic polypropylene: A high pressure study
Authors: Brückner Sergio , Phillips Paul J. , Mezghani Khaled , Meille Stefano V. 
Published: April 2003

AbstractThe non‐parallel chain structure determined for γ‐phase isotactic polypropylene (γ‐iPP) is confirmed by Rietveld analysis for highly isotactic high molecular mass iPP crystallized at 200 MPa. The new refinement shows that: (i) stereoregularity or crystallization pressure do not significantly influence the lattice dimensions; (ii) defect inclusion in γ‐iPP crystals is unlikely. The α and γ forms have nearly identical bulk internal energy and density, but α‐iPP should be normally kinetically favored over γ‐iPP which may in turn predominate due to its greater ability to host defects at the crystalline‐amorphous interface.
Crystal structure and crystallinity of poly(aryl ether biphenyl ether ketone ketone)
Authors: Liu Tianxi , Mo Zhishen , Wang Shanger , Zhang Hongfang , Na Hui , Wu Zhongwen 
Published: April 2003

AbstractThe crystal structure of poly(aryl ether biphenyl ether ketone ketone) (PEDEKK) was determined to comprise a two‐chain orthorhombic unit cell with dimensions a = 0.778 nm, b = 0.606 nm and c = 2.375 nm by using wide‐angle X‐ray diffraction (WAXD). According to the orthorhombic system, the 12 reflections of this polymer were indexed. The crystallite size increases with increasing the crystallization temperature. The results of the degree of crystallinity (Wc,x) calculated from WAXD were compatible with those from density (Wc,d) and calorimetry (Wc,h) measurements.
Preparation of a uniform poly(methyl methacrylate) macromonomer and its polymerization
Authors: Hatada Koichi , Nishiura Takafumi , Kitayama Tatsuki , Hirotani Shuji 
Published: April 2003

AbstractSyndiotactic poly(methyl methacrylate) (st‐PMMA) macromonomer having methacryloyl end group was prepared from st‐PMMA living anion and separated into uniform macromonomers by means of supercritical fluid chromatography. A uniform macromonomer with the degree of polymerization of 32 was polymerized radically in benzene at 60°C. The uniform dimer, trimer and tetramer of the uniform macromonomer were isolated from the polymerization product by means of gel‐permeation chromatography (GPC). The intrinsic viscosity ([η]) in tetrahydrofuran of these uniform comblike polymers was determined by GPC/differential viscometric analysis. The plot of logarithmic [η] against logarithmic molecular weight indicated that the trimer and tetramer assume a little shrinking molecular shape as compared with the unimer and dimer.
New side‐chain poly(methacryl‐rotaxanes) bearing cyclodextrins as non‐covalently anchored ring components. Chemoenzymatic synthesis and degradation
Authors: Noll Olaf , Ritter Helmut 
Published: April 2003

AbstractThe chemoenzymatic synthesis of new side‐chain polyrotaxanes (6) bearing non‐covalently attached cyclodextrins is described. Starting from 11‐methacryloylaminoundecanoic acid, up to 8 units of 12‐hydroxylauric acid were condensed in the presence of a lipase from Candida antarctica. They were copolymerized with methyl methacrylate to comb‐like polymers (4) bearing free carboxylic groups at the end of the oligoester side chains. These free carboxylic groups were then condensed chemically with a nucleophilic barrier group, N‐(4‐aminobutanoyl)‐4‐triphenylmethylaniline (5), in the presence of dimethylated β‐cyclodextrin, yielding new polyrotaxanes that contain statistically more than 1 ring component per side chain.
Smectic A liquid single crystal elastomers showing macroscopic in‐plane fluidity
Authors: Nishikawa Etsushi , Finkelmann Heino , Brand Helmut R. 
Published: April 2003

AbstractThe mechanical response of a smectic A liquid single crystal elastomer (LSCE) to stress applied perpendicular and parallel to the layers is described. We find that the static modulus perpendicular to the layers is two orders of magnitude larger than the modulus parallel to the layer direction, where the latter is completely due to the crosslinking. Macroscopically the width of the smectic A LSCE does not shrink when a mechanical stress is applied parallel to the layers while the length of the film increases by a factor of 2 thus demonstrating the in‐plane fluidity of the smectic layering.
Dual influence of lithium chloride on the reactivity of polystyryllithium in ethereal solvents
Authors: Van Beylen Marcel , Van Lierde Paul , Zimm Bruno H. , Szwarc Michael 
Published: April 2003

AbstractAddition of LiCl to ethereal solutions of polystyryllithium retards propagation of the polymerization at low polymer concentration, but accelerates it at higher polymer concentrations. This phenomenon is accounted for by the dual action of LiCl. Its dissociation yielding free common Li+ ions which diminish the concentration of the reactive free polystyryl anions dominates at low electrolyte concentrations. However, at their higher concentrations the Li+ scavenging action of LiCl, resulting in the formation of LiClLi+ triple ions, becomes important, it reduces the concentration of the free Li+ ions and increases, therefore, the proportion of the reactive free polystyryl anions.
Propene polymerization with Ziegler‐type catalysts formed from Me2Si(Ind)2ZrMe2 and cation‐generating reagents
Authors: Hahn Sabine , Fink Gerhard 
Published: April 2003

AbstractKinetic and polymer analytical results obtained with the systems Me2Si(Ind)2ZrMe2/[B(C6F4Si(i‐Pr)3)4]− [(C6H5)3C]+ (2) and Me2Si(Ind)2ZrMe2/[B(C6F5)4]− [(C6H5)3C]+ (3) in olefin polymerizations are compared (Me: methyl; Ind: indenyl). Both systems show that the polymerization rate increases with increasing metallocene concentration in a surplus due to the formation of binuclear species. The expected influence of increasing cation‐anion distance on the stereo‐errors of the poly(propylene)s when changing from system 3 into system 2 could not be detected.