bluuebunny/crossref_metadata_2025 huggingface dataset:
In vivo characteristics of low‐molecular‐weight copoly(L‐lactic acid/DL‐hydroxyisocaproic acid) with parabolic‐type and S‐type degradation pattersn
Authors: Fukuzaki Hironobu , Yoshida Masaru , Asano Masaharu , Kumakura Minoru , Mashimo Tooru , Yuasa Hisako , Imai Kyoichi , Yamanaka Hidetoshi
Published: April 2003

An amorphous copolyester of L‐lactic acid (LA) and DL‐hydroxyisocaproic acid (HICA) with a number‐average molecular weight (Mn) of 1600–4800 was synthesized by direct copolycondensation in the absence of catalysts, in order to develop a biodegradable carrier for drug delivery systems. The in vivo degradation pattern was changed into an S‐type from a parabolic‐type with an increase in molecular weight of copolyester. A luteinizing hormone‐releasing hormone agonist, des‐Gly10‐[D‐Leu6]‐LH‐RH ethylamide, was incorporated into a fine cylindrical copolyester formulation by the so‐called melt‐pressing technique. When the S‐type degradable and releasable copoly(LH/HICA) (70/30 mol‐%) formulations with Mn = 2200 were implanted subcutaneously in the back of rats, the most reasonable serum drug level was observed during the first 15 weeks period, keeping constant at approximately 3,5 ng/ml.
Synthèse et application de diols isomolécularies aux résines polyuréthannes
Authors: Boutevin Bernard , Chaib Messaoud , Robin J. J.
Published: April 2003

Different methods of preparation of monodisperse diols were reviewed and a new synthesis of perfectly monodisperse macrodiol 5 is described, obtained by radical telomerization of monoester 3 b (prepared by esterification of 10‐undecenoic acid (3 a) with 1,6‐hexanediol) with dithiol 4. Macrodiol 5 was used to obtain prepolymers by reaction with aromatic or aliphatic diisocyanates (6 and 7). Finally, these prepolymers were extended by 1,4‐butanediol and led to polyurethanes. All the above products were analyzed by GPC, 1H NMR, and the resulting polyurethanes were tested mechanically. The study shows that monodisperse diols lead to better mechanical properties of the polyurethane than those obtained from polydisperse diols with equal molecular weight.
Diethynyl‐terminated siloxane‐based diamide. Preparation and polymerization
Authors: Mantecon Ana , Bartholin Michel , Garapon Jacques , Sillion Bernard
Published: April 2003

1,3‐Bis[3‐(4‐ethynylbenzoylamino)propyl]hexamethyldisiloxane (3) was prepared and characterized. The flexible central unit of this product enables the easy and through polymerization of ethynyl groups at moderate temperature (220°C). The structure of the product resulting from the thermal polymerization of this diamide could not be elucidated so far. The product has a rather high Tg (260°C) and keeps it properties up to 250°C. On heating for a prolonged period of time at this temperature or at a higher one, the amide bond is cleaved, as evidenced by TG and FTIR data.
Crosslinking reactions of polyphenylene type polymers containing acetyl end‐groups with bis(hydridosilyl) derivatives of o‐carborane alcohols
Authors: Teplyakov Mikhail M. , Khotina Irina A. , Dmitrenko Alla V. , Kovalyov Aleksei I. , Kalinin Valeri N. , Korshak Vasili V. , Ismailov Boris A.
Published: April 2003

Crosslinking reactions of prepolymers of the polyphenylene type carrying acetyl end‐groups, based on 4,4′‐oxydiacetophenone and acetophenone (FPP‐1), or 4‐acetylacetophenone and 4‐(4‐acetylphenoxy)phenyl‐o‐carborane (FPP‐2), by means of 20–80 wt.‐% of 1,2‐bis[hydrido‐(dimethyl)siloxymethyl]‐o‐carborane (1) were investigated. It was found that the prepolymer FPP‐1 is easily crosslinked in the presence of 30 wt.‐% of 1 at 300°C, and the prepolymer FPP‐2 at 350°C.
Soluble poly(1,4‐phenyleneethynylene)s
Authors: Giesa Reiner , Schulz Rolf C.
Published: April 2003

New monomers are described for the synthesis of rod‐like poly(1,4‐phenyleneethynylene)s with long flexible aliphatic side chains. By palladium catalyzed polycondensation soluble polymers with melting points around 100°C could be obtained. The molecular weight was estimated by GPC, VPO and elemental analysis: GPC showed a multimodale distribution with Pn = 9–15. NMR spectra were found to be in agreement with the assumed polymer structure, but signals of the acetylenic carbons could not be detected. A broad, structureless absorption with a maximum at λ = 410 nm is seen in the UV‐VIS‐spectra. The thermal decomposition of the substituted PPE's starts at about 400°C and is comparable to that of unsubstituted PPE in air.
Hydroxytelechelic polybutadiene, 12. Polymerization reactions between hydroxytelechelic polybutadiene with hexamethylene diisocyanate or 4,4′‐methylenedi(phenyl isocyanate). Kinetics of polymerization in toluene and in the bulk
Authors: Deschères Isabelle , Pham Quang Tho
Published: April 2003

Addition polymerization of hydroxytelechelic polybutadiene (HTPB) with hexamethylene diisocyanate (HMDI) with a mole ratio NCO/OH = 0,8 in dilute solution of toluene as well as in bulk follows apparent 3rd order kinetics. The polymerization rates are twice as sensitive to temperature as in toluene, an effect which is attributed to intra‐ and/or intermolecular (OH, OH) auto‐association. The three alcoholic functions in HTPB are catalyzed equally by dibutyltin dilaurate. Even with high excess of NCO, free alcoholic functions were found in the product. They were determined quantitatively in moulded polyurethane sheets from HTPB + HMDI and HTPB + 4,4′‐methylenedi(phenyl isocyanate) which should be partially crosslinked:
Determination of functionality and molecular weight distributions in α‐hydroxy‐ω‐benzyloxyoligo(1,3,6‐trioxocane)s using HPLC methods
Authors: Krüger Hartmut , Much Helmut , Schulz Günter , Wehrstedt Carla
Published: April 2003

The cationic ring‐opening polymerization of 1,3,6‐trioxocane(TO) in presence of benzyl alcohol occurs in accordance with the activated monomer mechanism. In addition to their molecular weight distribution the reaction products exhibit a distribution of their end‐functionality caused by transacetalization. Two‐dimensional chromatography, including size‐exclusion and high‐performance liquid chromatography, was used to characterize quantitatively the molecular weight and functionality distribution. The postulated mechanism leading to a functionality distribution is supported by the experimental results obtained.
Molecular weight distribution in the activated monomer polymerization with nonequal propagation rate constants
Authors: Szymański Ryszard
Published: April 2003

Equations are derived to calculate the molecular weight distribution (MWD) of polymer chains for polymerizations with nonequal propagation rate constants. The presented set of equations allows the determination of the relative propagation rate constants provided the mole fractions of the chains with different degrees of polymerization are known. Furthermore, the MWD function for a polymerization with linearly increasing propagation rate constants is given. Application of the presented relations to analyse the MWD of polymers obtained by activated monomer polymerization is proposed.
Influence of the addition of an aliphatic epoxide as reactive diluent on the cure kinetics of epoxy/amine formulations
Authors: Urbaczewski Eliane , Pascault Jean‐Pierre , Sautereau Henry , Riccardi Carmen C. , Moschiar Stella S. , Williams Roberto J. J.
Published: April 2003

The cure kinetics of two different diepoxy prepolymers and their mixtures with a single diamine was analyzed using size exclusion chromatography (SEC). One of the diepoxy prepolymers was based on bisphenol‐A diglycidyl ether (DGEBA), while the other one was the diglycidyl ether of 1,4‐butanediol (DGEBD), which is a typical reactive diluent. They were used either alone or as a 50% mixture (in equivalents). The cycloaliphatic diamine 4,4′‐diamino‐3,3′‐dimethyldicyclo‐hexylmethane (3DCM) was used in stoichiometric proportions in every formulation. SEC could be used to follow the conversion of each type of epoxy groups as a function of time, in the pre‐gel stage. The reaction rate followed an autocatalytic behavior (catalysis by OH groups) in every case. DGEBD was less reactive than DGEBA. Mixing of both diepoxy prepolymers led to an increase in the specific rate constant for DGEBD and a decrease of the one for DGEBA. This can be explained by the influence of the polarity of the reaction medium on the polymerization rate and the presence of chlorine impurities.
Synthesis and structural study of an ABA block copolymer consisting of poly(γ‐benzyl L‐glutamate) as the a block and poly(ethylene oxide) as the B block
Authors: Cho Chong‐Su , Kim Seon‐Woong , Komoto Tadashi
Published: April 2003

ABA‐type block copolymers composed of poly(γ‐benzyl L‐glutamate) (PBLG) as the A component and poly(ethylene oxide) (PEO) as the B component were synthesized by polymerization of γ‐benzyl L‐glutamate N‐carboxyanhydride initiated by primary amines located at both ends of the PEO chain. The morphology examined by transmission electron microscopy using ruthenium tetroxide staining revealed a lamellar type of microphase separation of the copolymers. From circular dichroism measurements in ethylene dichloride solution, as well as from infrared spectra measurements in the solid state, it was found that the polypeptide block exists in the α‐helical conformation, as in PBLG homopolymer. Wide‐angle X‐ray diffraction patterns for the block copolymers depend on the casting solvent and show basically similar reflections as the PBLG homopolymer.
Solvent dependence of lyotropic liquid‐crystalline phases of cellulose tricarbanilate
Authors: Siekmeyer Maria , Zugenmaier Peter
Published: April 2003

Cellulose tricarbanilate (CTC) represents a derivative of cellulose which is excellently suited for a systematic study of the formation of lyotropic liquid crystals with solvents containing ether, ester or keto groups. The dependence on temperature, concentration and on structural features of the solvents as well as the phase behaviour were investigated in detail, especially with glycols, the chemical constitution of which was varied with respect to the glycol chain length and to the end groups. CTC with a narrow molar mas distribution and a degree of polymerization (DP) between 30 and 500 was synthesized for this study through derivatization of cellulose with subsequent degradation and fractionation.
Asymmetric radical polymerization of (–)‐3‐p‐menthyl sorbate
Authors: Doiuchi Tohru , Dodoh Takeshi , Yamaguchi Hidemasa
Published: April 2003

The radical polymerization of (–)‐3‐p‐menthyl sorbate (2) was performed with azoisobutyronitrile (AIBN) as an initiator in benzene at 50°C. The chiral (–)‐menthyl group in the resulting poly‐2 was removed by hydrolysis in potassium hydroxide solution to give optically active poly(sorbic acid), indicating that an asymmetric induction took place during the polymerization. It was concluded from the results of ozonolysis and optical rotatory dispersion measurements on the poly(sorbic acid) that the asymmetry was induced only at 1‐position of the monomeric unit in the poly‐2 main chain.
Macrocyclic peptides, 4. Preparations and enantioface‐differentiating abilities of 27‐ and 36‐membered ring peptides containing N,N′‐ethylene‐bridged dipeptides and glycine
Authors: Yamashita Tetsushi , Maruo Joji , Fujimoto Atsuko , Shibata Kozo , Kojima Yoshitane , Ohsuka Akio
Published: April 2003

27‐ and 36‐membered ring peptides were prepared using glycine, (2S, 3′ S)‐4‐methyl‐2‐(2′‐oxo‐3′‐isobutyl‐1′‐piperazinyl) pentanoic acid (2) and (2S,3′ S)‐3‐phenyl‐2‐(2′‐oxo‐3′‐benzyl‐1′‐piperazinyl)propanoic acid as the units of peptides. The interactions of 1‐phenylethylammonium (1) and p‐methoxy‐1‐phenylethylammonium bromides (11) with these cyclic peptides were studied by 1H and 13C NMR measurements in CDCl3. It was found from these results that the peptides distinguish the enantiomers (R‐ and S‐isomers) of the substrates. Furthermore, it was shown that the enantioface‐differentiating abilities of 36‐membered ring peptides are superior to those of 27‐membered rings.
Molecular design of biodegradable functional polymers, 2 Poly(carboxylic acid) containing xylopyranosediyl groups in the backbone
Authors: Matsumura Shuichi , Maeda Shuichi , Yoshikawa Sadao
Published: April 2003

Polymer 2, containing unreacted xylopyranosediyl groups in the backbone, was prepared from xylan by the conversion of vicinal hydroxyl groups to carboxylic groups using periodic acid/sodium chlorite. 2 was found to be biodegraded quickly by the activated sludge. Arthrobacter sp. KM810 and Flavobacterium sp. KM811 were isolated as 2‐degrading strains. It was found that these strains biodegraded all molecular‐weight fractions of 2. 2 shows a good calcium sequestration capacity which is comparable to that of poly(sodium acrylate).
Polymères photoréticulables à unités cinnamiques, 1 Synthèse des monomères et polymérisation
Authors: Remmas Miloud , Soutif Jean‐Claude
Published: April 2003

The synthesis of cinnamic acid derivatives with a carbon‐carbon double bond in para position was studied by a Knoevenagel reaction with p‐chloromethylstyrene. The latter was obtained via a several‐step reaction from 2‐phenylethanol. The monomers can be polymerized by a free‐radical process without affecting the cinnamic group. Copolymerization is effective only with monomers such as maleic anhydride, p‐vinylbenzaldehyde or methyl methacrylate, having a π‐acid character like the cinnamic acid derivatives used in our study.
Grafting of a vinyl acetate/methyl acrylate mixture onto cellulose. Effect of temperature and nature of substrate
Authors: Fernández María Jesús , Casinos Ismael , Guzmán Gonzalo Martín
Published: April 2003

A mixture of vinyl acetate and methyl acrylate was grafted onto cellulose by using ceric ions as initiator. The influence of temperature, oxygen and of the nature of the polymeric substrate (mercerized cellulose and grafted cellulose) on the grafting parameters was studied. High temperatures favour homopolymerization more than grafting. Successive oxidation of cellulose by ceric ions suggests two types of reaction sites in cellulose. A gel effect occurs when high grafting yield is reached. Polymerization is inhibited by oxygen.
Effect of annealing on the thermal properties of poly(4‐hydroxybenzoate‐co‐p‐phenylene isophthalate)s
Authors: Tsai Hong‐Bing , Lee Chyun , Chang Nien‐Shi , Chang Shinn‐Jen , Chen Mei‐Sui
Published: April 2003

A series of poly(4‐hydroxybenzoate‐co‐p‐phenylene isophthalate)s (1) was prepared by melt polycondensation of 4‐acetoxybenzoic acid, p‐phenylene diacetate, and isophthalic acid followed by solid state polymerization. The thermal properties of the as‐made samples were found to be significantly different from the second run thermal properties. The copolyesters with the same thermal history were annealed at 270°C in the DSC at various time intervals, and the thermal properties were further determined by DSC. For different compositions, annealing had different effects on the thermal properties of the copolyesters. With increasing annealing time the transition temperature and transition heat of 1 containing 50 and 60 mol‐% of monomeric units (m. u.) of 4‐hydroxybenzoic acid (HBA50 and HBA60) were found to increase. The second run DSC curves of HBA40, HBA30 and HBA20 (containing 40, 30 and 20 mol‐% of 4‐hydroxybenzoic acid m. u.) show two endotherms; transition heat and transition temperature of the lower temperature transition increase with the annealing time, but the transition heat of the higher temperature transition decreases. Finally, only one endotherm was observed for long‐time annealing. The difference in thermal properties between the as‐made sample and the second run could be described as annealing effect during solid state polymerization.
Monomères acryliques à fonction carbonate cyclique, 2 Modification chimique de copolymères à groupements carbonate cyclique lateraux
Authors: Couvret Denis , Brosse Jean‐Claude , Chevalier Sammy , Senet Jean‐Pierre
Published: April 2003

Acrylic monomers with a cyclic carbonate function, their synthesis having been described previously, are used to synthesize copolymers with pendent cyclic carbonate side groups. Their chemical modification by ring opening addition reactions provides a convenient method for preparing functional polymers. The study of reactions with amines, on model compounds and on polymers, shows the possibility of obtaining a macromolecular network with crosslinking groups of carbamate type.
Poly(oxy‐1,4‐phenylene) macromonomers for polycondensation
Authors: Nießner Norbert , Heitz Walter
Published: April 2003

Macromonomers based on poly(oxy‐1,4‐phenylene) (POP) with end groups suitable for polycondensation were synthesized. In a one‐step reaction, α‐(2,5‐dimethoxyphenyl)‐ω‐bromooligo‐(oxy‐1,4‐phenylene) (3) was obtained by Ullmann reaction of 1‐bromo‐2,5‐dimethoxybenzene (2) and potassium 4‐bromophenolate (1). Ether bond cleavage with boron tribromide yields the α‐(2,5‐dihydroxyphenyl) derivative 5, a novel type of macromonomers. Cocondensation with tert‐butylhydroquinone and trifluoromethylterephthaloyl dichloride results in the formation of a liquid‐crystalline graft copolymer (7).
Synthesis and controlled release behaviour of esters from amylose and 1‐naphthylacetyl chloride
Authors: Sánchez‐Chaves Manuel , Arranz Félix
Published: April 2003

This work deals with the modification reaction of amylose with 1‐naphthylacetyl chloride using pyridine as catalyst and the DMF/LiCl system as solvent. The structure of the resulting polymers was determined by IR, 1H and 13C NMR spectroscopy. A linear dependence of the reaction rate on the concentration of polymer, 1‐naphthylacetyl chloride and pyridine was found. The activation energy was found to be 32,4 kJ/mol. The hydrolysis in the heterogeneous phase showed that the release of the active compound from tablets is dependent on the hydrophilic character of the modified amylose as well as on the pH value of the medium.
The use of activated benzyl vinyl ethers to control molecular weight in free radical polymerizations
Authors: Meijs Gordon F. , Rizzardo Ezio
Published: April 2003

The vinyl ethers, α‐benzyloxyacrylonitrile (4), methyl α‐benzyloxyacrylate (5), and α‐benzyloxy‐acrylamide (6), act as sulfur‐free chain transfer agents in the polymerization of methyl methacrylate (chain transfer constant Cx = 0,081–0.47), styrene (Cx = 0,036–0,14), methyl acrylate (Cx = 0,3–1,1), and vinyl acetate (Cx = 12–20) initiated by AIBN at 60°C. With methyl methacrylate and styrene, the conversions of the polymerizations are relatively unaffected by the vinyl ethers. With methyl acrylate and vinyl acetate, however, some retardation occurs. The activity of the compounds is compared with that of α‐benzyloxystyrene (1), which undergoes chain transfer by a novel free radical addition‐fragmentation pathway.
Conditions of microgel formation in homogeneous anionic polymerization of 1,4‐divinylbenzene
Authors: Okay Oguz , Funke Werner
Published: April 2003

A kinetic model of the homogeneous anionic polymerization of 1,4‐divinylbenzene (1,4‐DVB) in dilute solutions with instantaneous initiation and without cyclization and termination reactions is proposed. The monomer and pendant vinyl group conversions, degrees of polymerization of the primary chains and the crosslinking densities were predicted as a function of the reaction time as well as 1,4‐DVB and initiator (butyllithium) concentrations. The previous experimental data concerning the formation of the microgels can be explained using the kinetic mechanism of the polymerization reaction and neglecting cyclization. Calculations indicate that reactive 1,4‐DVB microgels can be synthesized in the whole concentration range of the initiator.
Free‐radical polymerization up to high conversion. A general kinetic treatment
Authors: Buback Michael
Published: April 2003

The dependence of propagation and termination rate coefficients on conversion in free‐radical polymerization is described by a purely kinetic model which considers contributions of segmental diffusion, translational diffusion, and reaction diffusion to termination and which also takes diffusion‐control of the propagation step into account. The kinetic scheme provides a satisfactory representation and interpretation of the termination rate coefficient measured in an extended range of conversion for ethylene, butyl acrylate, and methyl methacrylate polymerization. Reaction diffusion is of primary importance for termination at moderate and high conversion, which leads to fairly simple expressions for kinetic parameters even at conversions where the solution viscosity exceeds the pure monomer viscosity by several orders of magnitude.
Friedel‐Crafts acylations of crosslinked polystyrenes using ω‐halogenoacyl chlorides
Authors: Caze Claude , Hodge Philip
Published: April 2003

The Friedel‐Crafts acylation of various crosslinked polystyrenes, both microporous and macroporous, by ω‐halogenoacyl chlorides, a reaction used by others to functionalise polystyrenes, was carefully investigated. As judged by elemental analyses, the desired reaction to give ω‐halogenoacyl residues is always accompanied by side reactions. Infrared spectroscopy indicates that these include crosslinking and the introduction of carboxylic acid groups. The side reactions are less pronounced with the ω‐chloro compounds and with the 2% crosslinked microporous polymer. For many applications these side reactions will not be important, but in some cases an awareness of their occurrence could be crucial.
Characterization of methylalumoxane by means of gel permeation chromatography
Authors: Cam Darinn , Albizzati Enrico , Cinquina Patrizia
Published: April 2003

Characterization of methylalumoxane (MAO) by gel permeation chromatography reveals the presence of different oligomeric products. Using suitable series of columns and alkylaluminium compounds with known molecular weight, it is possible to obtain the average molecular weights of most species which are present in a sample of MAO. The study of the chromatograms reveals modifications in composition of the MAO oligomers in relation to the time of residence in solution at given temperatures.
Action of the cellulase multienzyme complex on the degree of polymerization of high‐molecular‐weight cellulose
Authors: Marx‐Figini Marianne , Blanco Silvia , Ellenrieder Guillermo v.
Published: April 2003

A study of the viscosity‐average degree of polymerization DPη as a function of time under the action of a cellulase multienzyme complex was carried out using Trichoderma Reesei QM9414 for the production of the enzyme complex and cotton cellulose with a DPη ≈ 6 800 as substrate. Simultaneously the fractions of material dissolved by the enzyme action during various times of hydrolysis were determined. The study revealed that the enzymatic hydrolysis of cellulose using the multienzyme complex comprises several consecutive stages, one stage of appreciably decreasing DP alternating with one in which the DP is nearly constant. The portion of cellulose transformed (through its degradation) to soluble products, however, increases continuously with time also in the stages of constant DP. These results permit the conclusion that there exists a synergism of endo‐ and exocellulases, and that within this synergism the hydrolytical cleavage of internal glucosidic linkages catalysed by the endoenzyme is a necessary first step. The statistical degradation of cellulose molecules generates new chain ends which are then susceptible to the action of exocellulases, provoking and end‐wise depolymerization process.
Catalytic hydrolysis of nitrophenyl esters by means of cyclodextrins in presence of poly(sodium styrenesulfonate)
Authors: Seo Toshihiro , Kajihara Taketoshi , Iijima Toshiro
Published: April 2003

The catalytic hydrolysis of various nitrophenyl esters by α,β‐ and γ‐cyclodextrins (CD) in the presence of poly(sodium styrenesulfonate) (3) was investigated. In each system, on addition of 3 the hydrolysis was accelerated. It is suggested that the acceleration is enhanced with increasing contribution of the hydrophobic interaction between polymer 3 and CD and/or the phenyl ester substrate. It was found that 3 increases the concentration of both CD and the substrate in the reaction sphere, maintaining its reactivity and the ability to include the substrate into DC. It is assumed that the hydrophobic moiety is more easily formed with increasing molecular weight of 3, and has a loose domain structure. The addition of ethanol or sodium chloride was found to affect the catalytic activity of β‐CD or the conformation of the polymer chain.
Effect of composition on the entanglement density in random copolymers
Authors: Lomellini Paolo , Rossi Anna Grazia
Published: April 2003

The plateau moduli of poly(styrene‐ran‐acrylonitrile) and poly[styrene‐ran‐(methyl methacrylate)] copolymers are investigated. Plots of the plateau moduli versus composition of the copolymers show a large negative deviation from linearity in both cases. Molecular weights between entanglements are determined from the plateau moduli. The experimental data are discussed in terms of models recently proposed for miscible blends. The physical picture emerges of a random copolymer as a “forced miscible blend”.
Low temperature modification of polymers by triazolinediones, 2. On the mechanism of the electrophilic aromatic substitution with 4‐substituted 1,2,4‐triazoline‐3,5‐diones
Authors: Kuhrau Martin , Stadler Reimund
Published: April 2003

4‐Phenyl‐1,2,4‐triazoline‐3,5‐dione (2, PTD), like other triazolinediones, reacts with electron‐rich aromatic compounds to give an electrophilic substitution. The reaction of PTD with poly(oxy‐2,6‐dimethyl‐1,4‐phenylene) (1, PPE) is studied by UV and IR spectroscopy. Based on the kinetic measurements, three stages of reaction can be distinguished: a slow induction period; a period with strongly increasing reaction rate associated with the formation of a strongly absorbing species, probably a charge‐transfer complex, and conversion of most of the PTD; and finally a period with a slow decay of the previously formed absorbing species. Experiments with urazole or trifluoroacetic acid added at the beginning of the reaction prove that the strong increase in the reaction rate is due to autocatalysis by the urazole groups formed during the course of the reaction. A mechanism is proposed to account for the experimental findings.
Investigation of sequences in a poly(butadiene‐co‐trimethylvinylsilane) by metathesis degradation
Authors: Hubmann Ewald , Hummel Klaus , Dösinger Marianne , Pongratz Thomas , Saf Robert
Published: April 2003

Poly(butadiene‐co‐trimethylvinylsilane) with a mole fraction of 13% trimethylvinylsilane was prepared with butyllithium as initiator. It was degraded by cross‐metathesis with (E)‐4‐octene or (Z)‐2‐butene in the presence of the catalyst WCl6/Sn(CH3)4. The mixtures of the degradation products were investigated by means of gas chromatography (GC)/mass spectrometry (MS) coupling; mass spectra of degradation products with 4‐octene are depicted and discussed. Sequences of up to six trimethylvinylsilane units inserted between 1,4‐linked butadiene were identified after degradation with 2‐butene. Trimethylvinylsilane inserted between 1,4‐ and 1,2‐linked butadiene was also found. Cyclohexenyl and cyclopentenyl compounds were the preferred cyclic metathesis products.
Catalytic activity of novel agglomerates composed of Fe4S42+and (MovO)3+species cross‐linked with a bulky difunctional ligand, 2,4,6‐trimethyl‐1,3‐benzenedithiolate
Authors: Ueyama Norikazu , Sugawara Takashi , Okamura Taka‐aki , Nakamura Akira
Published: April 2003

The (MoVO)3+‐containing [Fe4S4]2+agglomerate {(Ph4P)2[Fe4S4(tmbdt)2(MoVO)0,76]}n(tmbdt = 2,4,6‐trimethylbenzene‐1,3‐dithiolato) was synthesized by reaction of {(Ph4P)2[Fe4S4(tmbdt)2]}nand MoVOCl3(thf)2. The (MoVO)3+cation is coordinated to the sulfur ligands binding the [Fe4S4]2+core. The (MoVO)3+‐containing [Fe4S4]2+agglomerate exhibits catalytic activity for the reduction of azobenzene and phenylacetylene to hydrazobenzene and phenylethylene, respectively, by Et4NBH4inN,N‐dimethylformamide/alcohol.
Modified poly(ethylene‐co‐propene‐co‐1,4‐hexadiene) (EPDM) bearing acetylacetonato groups and its chelate crosslinking with Fe(III)
Authors: Huang Ying , Eichinger Bruce E.
Published: April 2003

Acetylacetonato group‐bearing poly(ethylene‐co‐propene‐co‐1,4‐hexadiene) (EPDM) was prepared and its chelate by crosslinking reaction with ferric salts. The hydroiodination of residual double bonds in the EPDM terpolymer under phase‐transfer conditions and the substitution of iodine atoms in the hydroiodinated EPDM by acetylacetonato groups were studied. The ligand exchange reactions of acetylacetone with ferric trifluoromethanesulfonate (Fe(TFS)3) or ferric chloride in THF were explored by UV/Vis spectroscopy to find optimum conditions for the formation of the chelate complex ferric acetylacetonate. The results indicate that these two ligand exchange reactions are equilibrium reactions, and the addition of an organic base such as triethylamine can make the reactions go to completion. The character of the anion in the ferric salts has a significant effect on the ligand exchange reactions, which may be attributed to the different dissociation tendency of FeX bonds. The ligand exchange reactions in the polymer systems were studied, and Fe(III)‐chelate complex crosslinked EPDM elastogels with gel fractions higher than 90% were prepared. The mechanism of the chelate complex formation in the polymer systems is similar to that in model compound systems.
Analysis of the linear methods of determining copolymerization reactivity ratios, 9. Penultimate systems with r2 = 0
Authors: Kelen Tibor , Tüdős Ferenc , Braun Dietrich , Czerwinski Wojciech K.
Published: April 2003

The copolymerization equation considering the penultimate unit effect, the so called penultimate model, takes a simplified shape in the case of r2 = 0 (monomer 2, M2, does not homopolymerize). For this case a method analogous to the conventional KT(Kelen‐Tüdős)‐transformation for estimation of r1 and r1′ is proposed. The new method was verified by literature data for the system styrene/fumarodinitrile, polymerized with benzoyl peroxide at 70°C, yielding r1 = 0,062 and r1′ = 0,812. Classification of copolymerization curves by means of the classical copolymerization model permits to distinguish between three curve‐types: r1 < 2 (alternation with respect to M2), r1 = 2 (linear diagram with slope 0,5) and r1 > 2 (non alternating system). The penultimate model permits to generate further curve‐types of “S”‐shape with r1 > 2 and r1′ > 2 or r1 > 2 and r1′ < 2 (r1 = r1′ for classically behaving systems and r1 ≠ r1′ for non‐classically behaving systems).
Relationships between transport and equilibrium properties in ternary systems of unbranched alcohol/3‐heptanone/poly(1‐vinyl‐2‐pyrrolidone)
Authors: Gavara Rafael , Campos Agustín , Figueruelo Juan E.
Published: April 2003

Intrinsic viscosities, [η], second virial coefficients, A2, and interaction potentials, g12, for the ternary systems alcohol (1)/3‐heptanone (2)/poly(1‐vinyl‐2‐pyrrolidone) (3), with the unbranched alcohols methanol, ethanol and 1‐propanol, were determined at 25°C. Taking into account the dependence of the viscometric interaction parameter, B, with the molecular weight of the polymer, the unperturbed dimensions parameter, KΘ, of the polymer was unambiguously obtained. Relationships between ΔKΘ (defined as ΔKΘ = ΔK − KΘ) and excess Gibbs energies, GE, and between excess viscosity, Δ[η], and GE allow to obtain equations relating A2 to ΔKΘ or to Δ[η]. Therefore, A2 can be evaluated from experimental data of [η].
Comments on some recent papers concerned with terpolymerizations involving maleic anhydride
Authors: Bevington John C. , Ebdon John R.
Published: April 2003

Differences between results for the compositions of terpolymers of styrene (S), maleic anhydride (MAH), and either methyl methacrylate or methyl acrylate may be due to the difference between the diluents used during the copolymerizations. It is agreed that the compositions of the copolymers are very different from those calculated on the basis of the appropriate binary copolymerizations. It is not certain that complexes of S and MAH are involved in the growth reactions.
Soluble poly(para‐phenylene)s, 3. Variation of the length and the density of the solubilizing side chains
Authors: Rehahn Matthias , Schlüter Arnulf‐Dieter , Wegner Gerhard
Published: April 2003

The synthesis of a variety of alkyl‐chain‐substituted poly(para‐phenylene) (PPP) derivatives, including those with systematically decreased density of side chains, is described, using for their preparation the Pd‐catalyzed polymerization method recently developed in Mainz (Mainz route to PPP's). The degrees of polymerization achieved range between 30 and 50, allowing the synthesis of structurally well‐defined and soluble PPP's with more than hundred 1,4‐phenylene rings attached to each other.
New polymer syntheses, 47. Synthesis of aromatic polyethers from silylated diphenols and activated dichloro‐substituted aromatics
Authors: Kricheldorf Hans R. , Jahnke Petra
Published: April 2003

Bis(trimethylsilyl)bisphenol‐A was condensed with 4,4′‐dichlorodiphenyl sulfone under various reaction conditions. Satisfactory yields and molecular weights of the resulting poly(ethersulfone)s were only obtained when the condensation was conducted in amide solvents (e. g., N‐methyl‐2‐pyrrolidone) in the presence of equimolar amounts of K2CO3. The purity of the solvent plays an important role for the molecular weights. By light scattering, weight‐average molecular weights (Mw's) up to 130000 were found. Further polycondensations were conducted with 2,6‐dichlorobenzonitrile, 2,6‐dichloropyridine or 3,6‐dichloropyridazine. For polyethers derived from 2,6‐dichlorobenzonitrile Mw's up to 106000 were found and for copoly(pyridine‐ether‐sulfone)s Mw's up to 220 000. The corresponding difluoroaromatics gave similar results. In contrast to the polycondensation of free diphenols with dihaloaromatics under alkaline conditions, no water is formed when silylated diphenols are used.
Influence of ethyl benzoate on copolymerization of styrene and 1‐hexene with the titanium‐based systems (α)‐TiCl3(H) and TiCl3 · 1/3 AlCl3
Authors: Benaboura Ahmed , Deffieux Alain , Sigwalt Pierre
Published: April 2003

The influence of ethyl benzoate (E.B.) on the copolymerization of styrene with 1‐hexene, initiated by isospecific Ziegler‐Natta catalysts α‐TiCl3(H)‐AlEt3 and TiCl3 · 1/3 AlCl3‐AlEt3 (mole ratio Al/Ti = 3), was examined. Ethyl benzoate was found to reduce the activity of the catalysts. In addition it leads, depending on the Ti catalyst, to opposite effects on the apparent reactivity order of the two monomers. Incorporation of styrene into the copolymers is reduced when E. B. is added to TiCl3 · 1/3 AlCl3‐AlEt3. On the contrary, a much higher incorporation of styrene is observed with α‐TiCl3(H)‐AlEt3 in the presence of E. B. For this system the calculated reactivity ratio varies strongly with increasing proportion of E. B.: for a mole ratio AlEt3/E. B. = 3, rS = 0,94 and rH = 1,46 and for AlEt3/E. B. = 2, rS = 8 and rH = 0,1. Changes in the stereoregularity of copolymers suggest that E. B. leads to an inhibition of the less stereospecific sites for TiCl3 · 1/3 AlCl3‐AlEt3, whereas its addition suppresses the stereospecificity of the α‐TiCl3(H)‐AlEt3 catalyst. Contributions of conventional cationic and/or radical processes to the copolymerization reaction were examined and may be ruled out.
Synthesis and in vitro degradations of low‐molecular‐weight copolyesters composed of L‐lactic acid and aromatic hydroxy acids
Authors: Imasaka Kazumichi , Nagai Tsuneji , Yoshida Masaru , Fukuzaki Hironobu , Asano Masaharu , Kumakura Minoru
Published: April 2003

L‐lactic acid (LA) was copolycondensed with various aromatic hydroxy acids such as p‐hydroxybenzoic acid (HBA), p‐hydroxyphenylacetic acid (HPAA), and p‐3‐(hydroxyphenyl)propionic acid (HPPA) in the absence of catalysts, in order to investigate the copolymerizability and in vitro degradation. The results of 1H NMR spectroscopy and gel permeation chromatography (GPC) showed that the reaction proceeds quantitatively, but the molecular weight of the copolyesters is relatively low. The in vitro degradation pattern of copoly(LA/HPPA) was changed into an S‐type from a parabolic‐type with increasing HPPA content in the copolyester, in contrast to only parabolic‐type for both copoly(LA/HBA) and copoly(LA/HPAA).
Radical polymerization and block copolymerization initiated with ceric salt/aldehyde redox system
Authors: Sun Yanhui , Chen Xiangning , Feng Xinde
Published: April 2003

Aldehyde compounds exhibit very high reactivities towards ceric salt in initiating polymerization of acrylamide. In the presence of aldehyde compounds, the rate of polymerization is 8 times as high as the rate initiated by ceric salt alone. In nitric acid solution, the rate of polymerization decreases, but the accelerating effect of aldehyde compound becomes more obvious. Polyether prepolymer with aldehyde and groups also shows high activity towards ceric salt, with a relative rate of polymerization up to ca. 15, which can initiate acrylamide polymerization to form a block copolymer. The polymerization of acrylonitrile and methyl methacrylate initiated with ceric salt/aldehyde were also investigated.
Novel organosilicon‐containing polymers for an oxygen permselective membrane
Authors: Nagasaki Yukio , Kurosawa Koichi , Suda Makoto , Takahashi Seiji , Tsuruta Teiji , Ishihara Kazuhiko , Nagase Yu
Published: April 2003

Synthesis and gas permeation measurements of several types of polymers from methylstyrene derivatives containing mono‐and bis(trialkylsilyl) group(s) were carried out. Upon radical homo‐and co‐polymerization of silicon‐containing monomers high‐molecular‐weight polymers were obtained. Results from gas permeation measurements showed that these types of silicon‐containing polymers exhibit fairly high oxygen permselectivity (ratio of oxygen and nitrogen permeation coefficients P/P = 3,1 − 4,6), keeping the oxygen permeation coefficients (P) in the range of between 1,4 · 10−9 and 4,5·10−9 cm3 (STP) · cm · cm−2 · s−1 · cmHg−1. From time lag measurements, it was found that permeation coefficients are dependent on the solubility of gases in the membranes rather than on diffusivity. Actually, the oxygen solubility coefficients increase with increasing silicon content in the polymers. Permselectivity of oxygen against nitrogen is governed by polymer constitution rather than by silicon content.
Fourier transform infrared spectroscopy of the polymorphic forms of syndiotactic polystyrene
Authors: Guerra Gaetano , Musto Pellegrino , Karasz Frank E. , MacKnight William J.
Published: April 2003

Infrared spectra of syndiotactic polystyrene exhibiting various crystalline forms and modifications, and in the amorphous state, are reported in this contribution. In addition to strong conformational effects, the spectra demonstrate striking effects of chain packing. Several infrared spectral differences also exist between the two crystalline forms which present a trans‐planer conformation of the chains. Spectral changes are also reported for solution‐crystallized samples, which depend on the solvent present in the clathrate compound formed with the polymers.
Simulation of coupled modification reactions of polymers, 6. Kinetic aspects of the incomplete two‐stage α‐substitution of 1,4‐polybutadiene coupled with partial double‐bond shift
Authors: Hummel Klaus , Martl Michael G.
Published: April 2003

The kinetics of α‐substitution of 1,4‐polybutadiene, coupled with partial double‐bond shift, is calculated using a system of differential equations. The results are compared with those obtained by computer simulation (Monte Carlo calculation). In the model, hydrogen abstraction at CH2 takes place with rate constant k1 and substituents R are introduced. Reactions at CHR follow with rate constant k2. The fractions of the groups CH2, CHR, CR2, CH and CR are determined as a function of the degree of substitution φ (number of substituents in a molecular/degree of polymerization). For low values of φ or k1/k2, the solution of rate equations (simplified by considering triads of groups) and simulation give almost identical results. Simulation alone shows that the substitution is incomplete in the fully reacted polymer and the final composition depends on k1/k2.
Gradient high performance liquid chromatography of polymers, 2. Characterization of block copolymers of decyl and methyl methacrylate synthesized via group transfer polymerization
Authors: Augenstein Michael , Müller Michael A.
Published: April 2003

Statistical and block copolymers of decyl (DMA) and methyl methacrylate (MMA) were synthesized via group transfer polymerization (GTP) and characterized by size exclusion chromatography (SEC) and gradient HPLC. For HPLC a normal‐phase solvent gradient of isooctane and THF was used; the chromatograms were recorded by evaporative light scattering detection (ELSD). The block copolymers were shown to contain substantial amounts of precursor homopolymer by gradient elution, even in those cases where SEC furnished a perfectly monomodal molecular weight distribution (MWD). Comparison of the respective HPLC elution characteristics demonstrated that block copolymers are more strongly retained than statistical copolymers of identical composition. Whereas the latter are eluted according to chemical composition, the elution of the block copolymers seems to be controlled by the length of the poly(MMA) block.
Immobilization of a block copolymer of styrene and quaternized 4‐vinylpyridine on latex and its effect on the cobaltphthalocyanine‐catalyzed oxidation of 2‐mercaptoethanol
Authors: van Streun Karel H. , Tennebroek Ronald , Piet Pieter , German Anton L.
Published: April 2003

To overcome mass transport limitations that are usually encountered on immobilizing highly active catalysts, cationic latex particles were used as support for tetrasodium phthalocyaninato‐cobalt(II)tetrasulfonate (2). The cationic. latex was prepared by emulsion copolymerization of styrene and divinylbenzene in the presence of a block copolymer from styrene and 4‐vinyl‐N‐methylpyridinium PS‐qPVP serving as surfactant. The latex‐bound system was found to considerably increase the reaction rate of the oxidation of 2‐mercaptoethanol in the presence of 2 as compared with the conventional polymer‐free system. Michaelis‐Menten kinetics was observed for all three systems investigated, that is the block copolymer‐stabilized latex system, the homogeneous block copolymer system and the quaternized 4‐vinylpyridine homogeneous homopolymer (qPVP) system. Although the stability of the latex and qPVP‐containing systems after successive runs is rather poor, this immobilization method shows the great potential value of anchoring highly active systems retaining high catalytic activity. The turnover number is increased on immobilizing the block copolymer compared with the homogeneous block copolymer solution. The Michaelis constant is hardly affected by immobilization. Due to conformational changes of the polymer chain on immobilization, a comparison between the latex system and the homogeneous system containing either homopolymer or block copolymer remains difficult.
Ionic conductivity and morphology of polymer electrolytes based on a side‐chain liquid‐crystalline polysiloxane containing oligooxyethylene spacers and 6‐cyano‐2‐naphthyl benzyl ether mesogens
Authors: Hsieh Chang‐Jyh , Hsiue Ging‐Ho , Hsu Chain‐Shu
Published: April 2003

Solid polymer electrolytes with different stoichiometries were prepared from solvent‐cast mixtures of alkali metal salts with the side‐chain liquid‐crystalline polysiloxane 2. Differential scanning calorimetry, optical polarizing microscopy, X‐ray diffraction, and conductivity measurements revealed that both morphology and conductivity of the obtained complexes are dependent on the salt content. For the complexes formed from 2 with LiSO3CF3, the formation of a homogeneous phase occurred approximately at the mole ratio LiSO3CF3 to oxyethylene unit of 1/2. The conductivity of the complex gradually increases with increasing mole ratio LiSO3CF3/OCH2CH2. The highest conductivity at ambient temperature achieved was 4,8 · 10−6 S · cm−1, which corresponds to the complex with a mole ratio LiSO3CF3/OCH2CH2 of 1/1. For all complexes obtained the temperature dependence of the conductivity displays an unusual behaviour in the temperature range belonging to the glassy and glass transition states of the polymer and an Arrhenius‐type behaviour in the temperature range belonging to the liquid‐crystalline state of the polymer. For the complexes formed from 2 with various alkali metal salts, the conductivity decreases in the order LiSO3CF3 > LiClO4 > NaClO4 > LiBr > KClO4. This indicates that LiSO3CF3 is more effectively ionized by the oxyethylene units than the other salts.
The polarity of chain packing in native cellulose. A meridional electron diffraction analysis onvaloniafibres
Authors: Macchi Edgardo M.
Published: April 2003

The classical problem of chain‐packing polarity in native cellulose fibres is approached by electron‐diffraction analysis in fibrils of the algaValonia ventricosa. Meridional reflections up to the 12th layer line were registered and compared with the intensities calculated for one‐dimensional parallel and antiparallel models of the structure, projected upon thec‐axis. The results are compatible with cellulose molecules packed in parallel fashion, and with a stagger of the central chain with respect to that at the origin of +2,80 or +2,39 Å. Some consequences of the parallel structure with regard to the biogenesis of cellulose are discussed.
The effects of variation of a core ring system in the mesogenic side chain of liquid‐crystal polysiloxanes
Authors: Gray George W. , Hill Jonathan S. , Lacey David
Published: April 2003

Fourteen novel side‐chain polysiloxanes 2 and their alkene precursors 1 containing methylene‐cyclohexane, cyclohexane, benzene, bicyclooctane, 3‐oxobicyclooctane, bicyclohexane and biphenyl moieties in the mesogenic core, and with (CH2)n spacer lengths of n = 3, 6 and 11 are reported. The order of efficiency of these cyclic moieties in promoting liquid‐crystal properties in the polymers is the same as that observed for the precursor alkenes, indicating that similar qualitative structural rules govern mesophase type and thermal stability in both monomeric and macromolecular systems. The apparent occurrence of smectic C properties for two of the polymers is particularly interesting.
Studies of the metathesis polymerization and copolymerization of syn‐ and anti‐7‐methylnorbornene initiated by the tungsten‐carbene complex
Authors: Kress Jacky , Ivin Kenneth J. , Amir‐Ebrahimi Valia , Weber Patrick
Published: April 2003

The tungsten‐carbene complex was used to initiate the metathesis polymerization of syn‐and anti‐7‐methylbicyclo [2.2.1] hept‐2‐ene (Ms and Ma). Two kinds of experiment were performed:(i) the reactions were followed at low monomer/initiator ratios by 1H NMR spectroscopy at 220–250K; (ii) polymers and copolymers of Ms and Ma were prepared at room temperature and their microstructure analysed by 13C NMR spectroscopy. The propagating tungsten‐carbene species derived from both Ma could be detected. Some rate constants were evaluated for various steps in the mechanism. A polymer of Ms was prepared for the first time, containing 90% trans double bonds and probably isotactic. After hydrogenation this polymer exhibits two first‐order transitions, with DSC maxima at 179 and 230°C. Hydrogenated atactic polymers of Ma and of norbornene also exhibit first‐order transitions. Conditions are described for the preparation of block and tapered block copolymers of Ma and Ms.