bluuebunny/crossref_metadata_2025_split huggingface dataset:
Radical concentrations, environments, and reactivities during crosslinking polymerizations
Authors: Anseth Kristi S. , Anderson Karin J. , Bowman Christopher N. 
Published: April 2003

AbstractRadical environments and concentrations during the crosslinking polymerizations of multiethylene glycol dimethacrylates were characterized with electron spin resonance spectroscopy. The relative concentrations of free and trapped radicals were used as a measure of certain structural features in the evolving polymer, especially with respect to microgel formation. The influence of monomer structure and crosslinking density on the polymer structure was studied by examining the radical behavior during the polymerization of diethylene glycol dimethacrylate, poly(ethylene glycol 200) dimethacrylate, and poly(ethylene glycol 600) dimethacrylate. The extent of radical trapping and microgel formation was found to increase with increasing crosslinking density. The influence of the rate of initiation on radical trapping was also investigated, and slower rates of polymerization led to a higher fraction of trapped radicals with respect to the total radical population. Finally, the termination mechanism of radicals was characterized (long‐term and short‐term) and the corresponding kinetic constants quantified.
Infrared analysis on blends of poly(3‐hydroxybutyric acid) and stereoregular poly(vinyl alcohol): influence of tacticity of poly(vinyl alcohol) on crystallization of poly(3‐hydroxybutyric acid)
Authors: Ikejima Tetsuya , Yoshie Naoko , Inoue Yoshio 
Published: April 2003

AbstractThe extens of crystallization of poly(3‐hydroxybutyric acid) (P(3HB)) in blends of P(3HB) with stereoregular poly(vinyl alcohol) (PVA) have been studied by means of infared spectroscopy. The degree of crystallinity of P(3HB) was found to decrease by blending with atactic PVA when PVA was the predominant component of the blend. In P(3HB) blends with highly syndiotactic PVA, a significant suppression of P(3HB) crystallization was observed in a wider range of blend composition than that in P(3HB)/atactic PVA blends. These results are consistant with previous results obtained by means of solid‐state13C nuclear magnetic resonance and differential scanning calorimetry. In blends with highly isotactic PVA, P(3HB) was found to crystallize in the same way as in pure P(3HB).
Copolyesteramides, 9. Random 6‐iminohexanoyl/12‐oxydodecanoyl copolyesteramides
Authors: Goodman Isaac , Rodríguez Maria Teresa 
Published: April 2003

AbstractRandom copolyesteramides composed of NH(CH2)5CO (6A) and O(CH2)11CO (12E) units were prepared by co‐polymerization/condensation of 6‐hexanolactam with 12‐hydroxydodecanoic acid. Lactam elimination during the reactions limited the attainable 6A content to ca. 70 mol‐%. The properties of the materials differ markedly from those of the isomeric O(CH2)5CO/NH(CH2)11CO random copolymers. Those with up to 20 mol‐% 6A units are crystalline and essentially modified 12E polymers. Thereafter, up to ca. 55 mol‐% 6A, the materials were of an intermediate, relatively homogeneous phase character, a discrete polyamide phase appearing incipiently only at still higher 6A contents. The random nature of the copolymers was confirmed by 13C NMR spectroscopy, and IR examination showed the prevalence of amide‐ester hydrogen bonding at lower 6A contents together with a degree of intramolecular sub‐crystalline order in the 12E component over the range from 20–60 mol‐% 6A. It is suggested that the copolymer texture in this range is largely controlled by the preferred conformation of the (CH2)11 units of the ester component. Some properties, including the unit cell parameters, of the little‐known 12E polyester, [poly(12‐oxydodecanoyl)], are reported.
Biodegradable and pH sensitive hydrogels: synthesis by a polymer‐polymer reaction
Authors: Ghandehari Hamidreza , Kopečková Pavla , Yeh Ping‐Yang , Kopeček Jindřich 
Published: April 2003

AbstractpH sensitive hydrogels containing azoaromatic crosslinks were synthesized by a polymer‐polymer reaction. To minimize cyclization, a three step synthesis was employed. First, a polymeric precursor (P‐ONp) containing side‐chains terminated in reactive p‐nitrophenyl ester groups was synthesized by free radical precipitation copolymerization of N,N‐dimethylacrylamide, acrylic acid, N‐tert‐butylacrylamide, and N‐methacryloylglycylglycine p‐nitrophenyl ester. In the second step, the p‐nitrophenyl ester groups of P‐ONp were converted to NH2 groups (P‐NH2) by a polymer‐analogous reaction with an excess of a diamine, namely N,N′‐(ω‐aminocaproyl)‐4,4′‐diaminoazobenzene. The hydrogel was then prepared in the third step by a polymer‐polymer reaction of P‐ONp with P‐NH2. The linear copolymers were characterized by the content of functional groups and molecular weights. The hydrogels were characterized by equilibrium degree of swelling, modulus of elasticity in compression at pH 7.4, the network structure, and in vitro degradability. The swelling, mechanical properties, and rate of degradation depended on the crosslinking density. Although we were able to restrict cyclization, other side reactions such as unreacted pendent groups and hydrolysis need to be controlled. These hydrogels have potential for colon‐specific drug delivery.
Synthesis and characterization of poly(ether ketone)/poly(ether sulfone) alternating and sequential copolymers by electrophilic reactions
Authors: Finocchiaro Paolo , Montaudo Giorgio , Mertoli Patrizia , Puglisi Concetto , Samperi Filippo 
Published: April 2003

AbstractThe synthesis and NMR characterization of some poly(ether ketone)/poly(ether sulfone) (PEK/PES) alternating copolymers together with a series of sequential homopolymers containing CO, O, S and SO2 bridging groups, all obtained by electrophilic condensation reactions using phosphorus pentoxide/methanesulfonic acid as dehydrating agent, is here reported. Properties of such polymers are compared with those of their model compounds from which it can be inferred that both proton and carbon chemical shifts are very sensitive to the electronic environment generated by the O, S, CO and SO2 bridges. Differential scanning calorimetry indicates that our polymers are essentially amorphous irrespective of the bridging sequence. From viscosity measurements the molecular weights of these copolymers are judged to be very low.
Phase transitions of hydroxy‐telechelic side‐chain liquid crystalline polyethers and polyurethane networks derived thereof
Authors: Reesink Johannes B. , Picken Stephen J. , Witteveen Arend J. , Mijs Willem J. 
Published: April 2003

AbstractHydroxy‐telechelic polymers with side‐chain mesogenic groups have been prepared from epoxy monomers using a BF3/1,6‐hexanediol initiating system. Homopolymers showed either nematic or smectic A and C phases, depending on the length of the alkoxy substituent on the aromatic mesogenic group. In copolymers both nematic and smectic phases could be observed, depending on composition. Liquid crystallinity was found to be retained after crosslinking with a triisocyanate at temperatures below the clearing temperature of the mixture. On the other hand, the mesophase was found to disappear on rapid cooling after a certain degree of crosslinking above the clearing temperature, only to reappear after a period of heating above the glass transition temperature.
Low molar mass and oligomeric hexazadienes. Synthesis, thermolysis and photolysis
Authors: Nuyken Oskar , Scherer Cliff , Voit Brigitte 
Published: April 2003

AbstractSeveral new low molar mass 1,6‐diarylhexazadiene model compounds and a oligomeric structure, containing hexazadiene units in the main chain, were prepared by N‐N‐coupling of aromatic diazonium salts with hydrazine derivatives. Thermolytic and photolytic decomposition of these labile compounds have been studied in detail. A strong dependence of the decomposition rate on the substitution pattern was observed. Electron donating aromatic substituents as well as methyl groups at N3 and N4 position decrease stability in photolysis and thermolysis. On the other hand electron withdrawing aromatic substituents and acetyl groups at N3 and N4 stabilize the hexazadiene unit. Kinetics analysis showed that in some cases the decomposition reaction may be described by unimolecular one step pathway. Activation energies and rate constants have been evaluated. The oligomeric hexazadiene exhibits a somewhat higher stability towards heat and light compared to the low molar mass model compounds.
Preparation of poly(2‐glucosyloxyethyl methacrylate)‐concanavalin A complex hydrogel and its glucose‐sensitivity
Authors: Miyata Takashi , Jikihara Atsushi , Nakamae Katsuhiko , Hoffman Allan S. 
Published: April 2003

AbstractA glucose‐sensitive hydrogel was prepared by introducing concanavalin A (Con. A) into poly(2‐glucosyloxyethyl methacrylate) (poly(GEMA)) hydrogel. The decrease in swelling ratio and increase in crosslinking density by introduction of Con. A into the poly(GEMA) hydrogel indicate that the complexation introduces additional crosslinking points. The swelling of the hydrogel increased in the presence of glucose, and the swelling ratio was dependent on the glucose concentration. The glucose sensitivity of the hydrogel is attributable to the dissociation of the complex between poly(GEMA) and Con. A in the presence of glucose. Furthermore, the poly(GEMA)‐Con. A complex hydrogel was responsive to the kind of monosaccharide; its swelling ratio was changed by the presence of glucose or mannose, but not by the presence of galactose. The swelling properties of this hydrogel might be useful for the development of a glucose‐sensitive device.
Effect of tacticity on enzymatic degradability of poly(β‐hydroxybutyrate)
Authors: Timmins Mark R. , Lenz Robert W. , Hocking Philippa J. , Marchessault Robert H. , Fuller R. Clinton 
Published: April 2003

AbstractFilms of synthetic poly(β‐hydroxybutyrate)s (PHB)s ranging from highly isotactic to moderately syndiotactic were cast from each of several polymer fractions isolated from ring‐opening polymerizations of racemic β‐butyrolactone and were subjected to degradation by the extracellular PHB depolymerases of the bacterium Pseudomonas lemoignei and the fungus Aspergillus fumigatus M2A. Films of bacterially produced PHB were also degraded for comparison. Gravimetric determinations of enzymatic degradation were measured relative to control experiments in which no depolymerase was added. Each sample was exposed to the same concentration of enzyme, as determined by the activity of the enzyme solutions towards bacterial PHB powder, and the degradation behavior varied strongly with the tacticity of the samples. Weight loss was greatest for the bacterial polymer, with films being completely degraded by either enzyme in 48 h. The degradation of the synthetic samples by both enzymes followed similar trends, although the fungal depolymerase effected less rapid degradation for all synthetic samples than did the bacterial enzyme. Of the synthetic PHB samples, those of intermediate tacticity (55–60% isotactic diads) exhibited the greatest rate of weight loss, while those most syndiotactic in nature (34–45% isotactic) degraded the most slowly. The observed rates are interpreted in terms of isotactic contents, tacticity sequence distributions, and sample crystallinities.
Photosensitized cationic polymerization using allyl sulfonium salt
Authors: Denizligil Selcuk , Resul Rezan , Yagci Yusuf , Mc Ardle Ciaran , Fouassier Jean‐Pierre 
Published: April 2003

AbstractThe cationic polymerization of cyclic ethers such as cyclohexane oxide (CHO) and vinyl monomers such as butyl vinyl ether (BVE) and N‐vinylcarbazole (NVC) is initiated upon irradiation at λ 380 nm in CH2Cl2 solution containing an allylic sulfonium salt, namely, 2‐ethoxycarbonyl‐2‐propenylthiophenium hexafluoroantimonate (1) (EMT+SbF6−), and one of the following compounds: benzophenone, anthracene, thioxanthone, perylene or phenothiazine. Electron transfer and hydrogen abstraction mechanisms were proposed for the initiation step. Stable cation radicals of phenothiazine were also prepared, and the cationic polymerization of butyl vinyl ether was initiated by these cation radicals.
Synthesis and optical properties of a novel soluble polycarbazolyldiacetylene
Authors: Colombi Claudio , Comoretto Davide , Cuniberti Carla , Musso Gianfranco , Piaggio Paolo , Dellepiane Giovanna , Novi Marino , Dell'Erba Carlo , Bolognesi Alberto 
Published: April 2003

AbstractA novel soluble polydiacetylene with 3,6‐dialkyl‐substituted carbazolyl side groups (polyDCHD‐S) has been prepared. Its electronic and vibrational properties have been studied in the crystalline state. The results are compared with those of polyDCHD taken as reference. PolyDCHD‐S shows a very high conjugation length like polyDCHD but an increased interchain separation. High non‐linear optical response is then expected; that — together with the processability of the polymer — suggests attractive applications in photonic devices based on thin film technology.
Catalytic polycondensations of bis(trimethylsilyl) p‐xylylene ethers with elimination of hexamethyldisiloxane and their related reactions
Authors: Yokozawa Tsutomu , Nishimori Makoto , Endo Takeshi 
Published: April 2003

AbstractFor establishment of the catalytic polycondensation with elimination of hexamethyldisiloxane, etherification of benzylic trimethylsilyl ethers 2 as a model reaction and polymerization of bis(trimethylsilyl) p‐xylylene ethersSystematic name: α,α′‐bis(trimethylsiloxy)‐p‐xylenes.
1 were carried out with Lewis acids. Benzyl trimethylsilyl ether (2a) was reacted with 5 mol‐% of trimethylsilyl trifluoromethanesulfonate (Me3SiOTf) in dichloromethane at 25°C for 24 h to afford dibenzyl ether (3) in 40% yield. The yield of 3 decreased with time after 24 h because the ether linkage of 3 was cleaved also with Me3SiOTf to generate benzyl cation which underwent Friedel‐Crafts reaction. During the study of catalysts and solvents in this reaction, the reaction of 2a with Me3SiOTf in diethyl ether at 25°C was found to depress considerably the Friedel‐Crafts reaction. Further, the etherification of a secondary benzylic silyl ether, α‐phenethyl trimethylsilyl ether (2b), with Me3SiOTf proceeded rapidly in diethyl ether at 25°C to yield the corresponding dibenzylic ether in good yield. On the basis of the results of the model reaction, the polymerizations of difunctional benzylic silyl ethers, bis(trimethylsilyl) p‐xylylene ether (1a) and α,α′‐dimethyl‐p‐xylylene bis(trimethylsilyl) ether (1b), were carried out with Me3SiOTf in diethyl ether. In the polymerization of 1a, a polyether with low molecular weight (Mn = 2000) was obtained as well as a cross‐linked polymer formed by the Friedel‐Crafts reaction. In the polymerization of 1b, the molecular weight of the polymer increased with time to 9000, then decreased gradually accompanied by the production of cross‐linked polymer after 5 days. The polyether obtained from 1b could not be prepared by the Williamson ether synthesis, because the intramolecular elimination of hydrogen bromide from α,α′‐dimethyl‐p‐xylylene dibromide predominantly took place.
Cryochemical synthesis and structure of metal‐containing poly(p‐xylylenes): system poly(chloro‐p‐xylylene)‐Ag
Authors: Gerasimov Genrikh N. , Sochilin Vladimir A. , Chvalun Sergei N. , Volkova Larisa V. , Kardash Igor Ye. 
Published: April 2003

AbstractPolymer films with small Ag‐clusters and Ag‐nanocrystals were obtained by the cocondensation of Ag and chloro‐p‐xylylene from the gaseous phase followed by low‐temperature solid‐state polymerization. UV‐Vis spectroscopic data show that the annealing of films at ambient temperature and thereafter at 373 K leads to a sharp rise of the amount of Agnanocrystals by aggregation of small clusters, but the mean size l̄ of the nanocrystals remains practically constant. According to X‐ray data, the lattice of Ag‐nanocrystals is close to that of metallic Ag and l̄ is equal to approximately 50 Å.
Stereoregularity of poly(methacryloyl chloride) and poly(methacrylic salts) prepared by photopolymerization
Authors: Chovino Christian , Gramain Philippe 
Published: April 2003

AbstractPoly(methacryloyl chloride) (PMACl) and poly(methacrylic tetramethylammonium salts) and poly(methacrylic tetraethyl ammonium salts) (PMAAN+) have been prepared by radical photopolymerization at different temperatures. The obtained molecular weights are independent of the polymerization temperature in the range studied (+24 to −30°C) which is in agreement with a purely photochemical process. The dependence of the tacticity upon temperature was examined by means of NMR spectroscopy. Deviations from Bernoullian statistics were confirmed. PMAAN+ salts prepared in water are highly syndiotactic and a nearly pure syndiotactic structure is obtained at +5°C. This behavior is explained by the repulsive interactions between the carboxylate anions promoting the racemic placement. The tacticity of PMACl is comparable with that of poly(methacryloyl fluoride). The structure is less syndiotactic and much more isotactic than that of poly(methyl methacrylate). This result is interpreted by considering the electron‐withdrawing character of chlorine and fluorine atoms which affects the electronic structure and polarity of the carbonyl group near to the macroradical and competes with the preferential syndiotactic placement observed with α‐substituted acrylates.
Vernetzte globuläre Proteine — eine neue Klasse halbsynthetischer Makromoleküle: Charakterisierung ihrer Struktur in Lösung am Beispiel hyperpolymeren Hämoglobins und Myoglobins mittels Volumenausschluß‐Chromatographie, Viskosimetrie, Osmometrie und Lichtstreuung
Authors: Pötzschke Harald , Barnikol Wolfgang K. R. , Kirste Rudolf G. , Rosenbaum Markus 
Published: April 2003

AbstractDeveloping an artificial oxygen carrier for use in humans, we polymerize native haemoglobin and myoglobin, using bifunctional, amino group specific cross‐linkers, to soluble, so‐called hyperpolymers. These polymers, like other polymerized globular proteins, are members of a new class of macromolecues which consist of macromolecular base units. They all have, due to the mechanisms of the chemical reaction, broad distributions of molecular weights. Fractions of hyperpolymers of human haemoglobin were obtained by employing preparative gel‐permeation (size‐exclusion) chromatography. The calibration curve of analytical gel‐permeation chromatography (GPC) for haemoglobin hyperpolymers was determined using mean molecular weights of some fractions, as assessed by osmometric and light scattering measurements. In analogy to native globular proteins, the calibration curve for haemoglobin polymers — within the range of molecular weights considered here, and within the experimental accuracy — is a straight line. All fractions of haemoglobin polymers were further characterized with the aid of calibrated analytical GPC. Mean non‐uniformity was about, 0,6. The dependence of the logarithm of the intrinsic viscosity [η] on the logarithm of the viscosity‐average molecular weightMηof the fractions (the curve in the “structure‐in‐solution diagram”) also is a straight line, which is true for haemoglobin and for myoglobin polymers as well. Its first derivative is the exponentaof the Mark‐Houwink function; for haemoglobin and myoglobin polymers the values are 0,39 and 0,46, respectively. Haemoglobin and myoglobin hyperpolymers, as members of the new class of polymers, both have a characteristic so‐called “structure‐in‐solution diagram”, and a characteristic calibration curve in GPC. The special structure‐in‐solution of the polymer proteins is a novel molecular superstructure. The intrinsic viscosity for native myoglobin was found to be 3,5 mL/g.
Synthesis and characterization of conjugated polymers with imino nitroxide groups
Authors: Saf Robert , Swoboda Petra , Lechner Andreas , Hummel Klaus , Czaputa Rainer 
Published: April 2003

AbstractTwo new conjugated polyradicals with imino nitroxide groups, poly[2‐(3,4‐diethynylphenyl)‐4,4,5,5‐tetramethylimidazolinyl‐1‐oxyl] (3) and poly[2‐(3,5‐diethynylphenyl)‐4,4,5,5‐tetramethylimidazolinyl‐1‐oxyl] (4), were prepared. Spectroscopic methods (IR, UV, ESR, MS) were used for the characterization. The polyradicals were precipitated from pyridine/methylene chloride solution by hexane and investigated magnetically. In the temperature range 78–300 K, polyradical 3 was paramagnetic. The magnetic behavior of polymer 4 pointed to very weak antiferromagnetism. The magnetic properties of 3 and 4 were compared to those of previously described corresponding polymers containing nitronyl nitroxide groups.
Kinetics of the polymerization of isoprene with isopropoxyneodymium dichloride/triethylaluminium binary lanthanide catalyst system
Authors: Cai Xiaoping , Gong Zhi , Wang Fosong , Zhu Xinghao 
Published: April 2003

AbstractThe kinetics of the polymerization of isoprene with the heterogeneous rare earth catalyst system isopropoxyneodymium dichloride/triethylaluminium (Nd(OPri)Cl2‐AlEt3) was examined in a specially designed dilatometer. The rate of polymerization is expressed as Rp ≈ −d[M]/dt = k[Nd]1.40 [M]. The main kinetical parameters such as the concentration of active propagating chain, the efficiency of lanthanide catalyst used (ELCU), the absolute rate constant of propagation as well as the average life time of growing chains, were determined at 30°C, 40°C, 45°C and 50°C.
Chromatographic separation and 13C NMR characterization of aromatic diester‐diacids isomers
Authors: Huang Wenxi , Gao Lianxun , Zhang Xin , Xu Jiping , Ding Mengxian 
Published: April 2003

AbstractReverse phase high performance liquid chromatography (HPLC) was used to separate and quantify aromatic diester‐diacids isomers which arise from the opening selectivity of anhydride rings towards methanol. 13C NMR spectroscopy was a supplementary tool to characterize the isomer structure. It was found that a meta‐position attack is slightly preferred in pyromellitic dianhydride (PMDA), while the preferred position of an attack in bridged dianhydrides is determined by the chemical nature (donors or acceptors) of the bridged group. The stronger its electron‐withdrawing abilities, the lower the probability of a meta‐position attack.
The effects of physical ageing on conformational changes of poly(ethylene terephthalate) in the glass transition region
Authors: Qian Renyuan , Shen Deyan , Sun Fuge , Wu Liheng 
Published: April 2003

AbstractIn‐situ FTIR studies on the conformational changes of poly(ethylene terephthalate) (PET) films with different thermal histories, i. e., quenched from the melt and sub‐Tg annealed at different temperatures, were carried out while increasing the temperature through the glass transition region. The temperature dependencies of the infra‐red spectra showed that incremental changes of the population of trans conformers in the quenched sample are gradual, while rather abrupt changes occur in the sub‐Tg annealed samples. The magnitude and temperature of the abrupt changes of trans conformers were related with the temperature of sub‐Tg annealing. An energy difference of 28.6 J/g between the trans and gauche conformational states was measured by the infra‐red spectroscopic method. The energy absorbed during the abrupt conformational change represents only part of the energy of the endothermic peak observed by differential scanning calorimetry. The results are explained in terms of the formation of new cohesional entanglements during sub‐Tg annealing.