bluuebunny/crossref_metadata_2025 huggingface dataset:
The morphology of poly(ethylene oxide)‐barium perchlorate complexes
Authors: Maunu Sirkka L. , Rinne Hannu , Sundholm Franciska
Published: April 2003

Poly(ethylene oxide) dissolves a wide variety of inorganic salts and forms solid complexes with multiphase structures. The interaction between polymer chains and ions directs the morphology of the sample. The structure is very sensitive to the preparation methods and the purity of the materials. In this work the morphology of poly(ethylene oxide)‐Ba(ClO4)2 complexes has been analysed. The effect of the salt concentration and the variations in the molar mass of the polymer was studied. The multiphase structures were investigated by infra‐red spectroscopy, differential scanning calorimetry, optical microscopy, 13C cross polarization and magic‐angle spinning NMR spectroscopy, and wide angle X‐ray scattering. Two different crystalline phases and changes in the amorphous phase were found for the complexes when the salt concentration was varied.
Configurational double bond selectivity in the epoxidation of hydroxy‐terminated polybutadiene with m‐chloroperbenzoic acid
Authors: Aguiar Marcelo , de Menezes Sonia Cabral , Akcelrud Leni
Published: April 2003

The selectivity of the three different double bonds (CIS, TRANS and VINYL) of hydroxyterminated polybutadiene regarding epoxidation was evaluated, using m‐chloroperbenzoic acid in toluene below room temperature (−10°C, −5°C, 0°C and 5°C). To determine the kinetic constants for the three configuratons (k1,cis = (2,59–0,6) × 10−2 L · mol−1 · min−1; k2, trans = (5,35–0,82) × 10−2 L · mol−1 · min−1; k3, vinyl = (0,97–0,01) × 10−2 L · mol−1 min−1), 1H and 13C NMR was used along with a system of three parallel equations. The activation energy values were also evaluated (Ea, cis = 53,9 kJ · mol−1; Ea, trans = 70,7 kJ · mol−1 and Ea, vinyl = 261,1 kJ · mol−1) for the three double bond types.
Ultrathin crosslinked membranes at the interface between oil and water
Authors: Burger Andreas , Leonhard Herbert , Rehage Heinz , Wagner Ronald , Schwoerer Markus
Published: April 2003

The tensio‐active properties of different types of diesters can be used to synthesize two‐dimensional model networks at the interface between oil and water. We have systematically studied rubber‐elastic, glass‐like and transient membranes, which are stabilized and crosslinked by physical or chemical contacts. The kinetics of surface gelation and the mechanical properties of the crosslinked membranes were investigated by measuring two‐dimensional rheological parameters, such as the shear modulus or the surface viscosity. The experimental data of these investigations are in fairly good agreement with the theoretical predictions of percolation theories. Further informations on the molecular structure of the crosslinked membranes can be obtained from electron spin resonance (ESR) measurements. Using spin labels of significantly different sizes, which are diffusing from the aqueous environment into the oil phase, it is possible to determine the average mesh size of the interfacial network structure. The systematic study of these ultrathin membranes offers new insights into aspects of current research, and opens interesting new technical applications.
Rheo‐optical characterization (flow‐birefringence and flow‐dichroism) of the Tobacco Mosaic Virus
Authors: Reinhardt Ulf T. , de Groot Eleanor L. Meyer , Fuller Gerald G. , Kulicke Werner‐Michael
Published: April 2003

Rheo‐optical techniques of determining flow‐birefringence Δn′ and flow‐dichroism Δn″ were employed to investigate a Tobacco Mosaic Virus (TMV) solution under steady‐state and relaxation conditions to obtain further information about molecular dynamics in terms of local and global orientation and flexibility. These effects were investigated in a concentration range of 0,5 g/L ⩽ c ≦ 2,89 g/L, i.e. below and above the critical overlap concentration c* = 2,45 g/L. Although some aggregation was unavoidable it was determined that in the region of c* the dynamic behaviour was not influenced by varying the concentration. Furthermore it was shown that these aggregates naturally appearing in TMV are sensitive to shear force and dissolve at shear rates above 1 s−1. Beyond the critical shear rate this rodlike molecule should show a good agreement of the orientation angles determined through dichroism and birefringence and a constant ratio Δn″/Δn′ which in fact was found. This reveals experimentally that in spite of the sensitivity to different length scales dichroism and birefringence exhibit similar responses to shear forces for rigid and monodisperse macromolecules.
Poly(methyl methacrylate) containing pyrrole moieties in the side chains
Authors: Hallensleben Manfred L. , Stanke Dietmar , Toppare Levent
Published: April 2003

Two synthetic routes to copolymers 7 of methyl methacrylate (MMA) with 2‐(N‐pyrrolyl)ethyl methacrylate (PEMA, 11) are compared. Copolymerization of MMA (4) with 2‐bromoethyl methacrylate (BEMA, 3) leads to a precursor copolymer 5. The reactivity ratios are close to unity (rMMA = 0,90, rBEMA = 0,92). The polymer‐analogous reaction of 5 with N‐pyrrolylpotassium (6) runs to 99% conversion of the BEMA units. The synthesis of PEMA (11) is presented. The reactivity ratios of copolymerization of this monomer (11) with MMA (4) are determined to rMMA = 1.05 and rPEMA = 1,65. Copolymers 7 are further characterized by 1H nuclear magnetic resonance, infrared spectroscopy, gel‐permeation chromatography and differential scanning calorimetry.
Study of interaction parameters in liquid mixtures
Authors: Zhu Peng Wei
Published: April 2003

The interactions in binary liquid mixtures were studied. The Flory‐Huggins interaction parameters are calculated. When the effects of concentration fluctuation and free volume on the interaction parameter are taken into account, the interaction parameters are found to be much smaller than the corresponding critical parameters.
Hexa‐n‐alkylcyclotrisiloxanes — synthesis, melting behaviour and polymerization
Authors: Out Gerhardus J. J. , Klok Harm‐Anton , Möller Martin , Oelfin Dieter
Published: April 2003

A homologous series of hexa‐n‐alkylcyclotrisiloxanes and poly(di‐n‐alkylsiloxane)s has been prepared with alkyl side groups varying in length between 4 and 10 carbon atoms. Melting transition enthalpies of the hexa‐n‐alkylcyclotrisiloxanes indicated a reversed odd‐even effect, showing higher melting enthalpies for cyclotrisiloxanes with n‐alkyl side groups with an odd number of carbon atoms. The melting behaviour of the heptyl‐ and octyl‐substituted cyclotrisiloxanes was rather complex. Multiple melting transitions could be observed, which are presumably due to formation of a kinetically favoured crystalline phase next to the thermodynamically stable crystal modification. All hexa‐n‐alkylcyclotrisiloxanes could be polymerized by anionic or cationic ringopening polymerization. The observation of longer polymerization times and formation of relatively larger amounts of cyclic byproducts in the case of hexadecylcyclotrisiloxane compared to hexaethylcyclotrisiloxane indicated that with increasing side group length, the anionic polymerization propagation rate constants kp decreased, whereas the rate constants of depolymerization kdx increased. Cationic polymerization with trifluoromethanesulfonic acid as the initiator, offered a way to enhance kp relative to kdx, which allowed the preparation of high molecular‐weight polymeric products in good yields even in case of cyclotrisiloxanes substituted with long n‐alkyl groups. Apart from poly(dimethylsiloxane), poly(diheptylsiloxane) and poly(dinonylsiloxane), all poly(di‐n‐alkylsiloxane)s showed two crystalline phases which were separated by a crystal‐crystal transition signifying melting of the side groups. Starting from poly(diethylsiloxane), poly(di‐n‐alkylsiloxane)s up to poly(dihexylsiloxane) displayed a hexagonal columnar mesophase as well, the stability of which increased with longer alkyl side groups. However, further elongation of the n‐alkyl side groups to decyl appeared to destabilize the columnar mesophase. Poly(didecylsiloxane) only exhibited a metastable columnar mesophase in combination with the high‐temperature crystalline phase.
Poly(cycloalkyl[c]thiophene)s — syntheses, electrical properties and charge transport mechanism
Authors: Rühe Jürgen , Berlin Anna , Wegner Gerhard
Published: April 2003

Poly(cycloalkyl[c]thiophene)s were synthesized by electrochemical or chemical oxidation of bicyclic, α,α′‐unsubstituted thiophenes. NMR measurements on neutral, soluble poly(cyclododeca[c]thiophene) indicate that the polymers have the expected linear structure. The optical spectra and the electrochemical properties of the films are reported. The electrical conductivity σ of salts of the polymers varies from 50 S/cm to 8 · 10−5 S/cm depending on the ring size of the substituent and degree of oxidation of the polymer backbone. A linear correlation between log σ and the diameter of the alkyl substituent demonstrates that interchain contacts play a dominant role in the conductivity of these polymers. The temperature dependence of the conductivity was measured in the range of 300 to 5 K and its frequency dependence in the range of 1–107 Hz at 300 to 120 K. The conductivity data were analyzed in terms of hopping of localized charge carriers and the localization length of the charge carriers was calculated.
Morphology and structure of organosilicon polymer‐modified epoxy resins
Authors: Zheng Sixun , Wang Haiqian , Dai Qizhou , Luo Xiaolie , Ma Dezhu , Wang Ke
Published: April 2003

An epoxy‐terminated organosilicon polymer (denoted as ETOP) was used as modifier to blend with bisphenol A type epoxy resins. For uncured epoxy resins/ETOP blends, the miscibility is mainly the contribution of entropy. The phase boundary was investigated. The turbidity points were determined on the basis of optical microscopic observation. While the aromatic amine curing agents were added to the systems, curing at higher temperature, an obvious phase separation between cured bisphenol A type epoxy resins (DGEBA) and ETOP was observed. The structure of the resulting cured products was investigated by differential scanning calorimetry (DSC), dynamic mechanical property analysis (DMA) and scanning electron microscopy (SEM). It is the very elastomeric phase (0,1–5 μm) that enhances the toughness of epoxy resins. Another significant phenomenon is that the crosslinked epoxy‐rich phase (matrix) possesses a higher glass transition temperature (Tg) than pure epoxy resins cured with an aromatic amine, particularly at a higher content of ETOP. This may be considered as participation of epoxide groups on ETOP molecules in the crosslinking reaction of matrix and enhancing the crosslinking density of the matrix (i.e., increasing the Tgs). The results provide ones a larger choice to improve the toughness of the epoxy resin without loss of substantial modulus and thermal resistance.
Copolymers of N‐vinyl‐2‐pyrrolidone and 2‐(dimethylamino)ethyl methacrylate, 1. Synthesis, characterization, quaternization
Authors: Deboudt Karine , Delporte Michèle , Loucheux Claude
Published: April 2003

2‐(Dimethylamino)ethyl methacrylate (DMAEM) — N‐vinyl‐2‐pyrrolidone (VP) copolymers were synthesized and characterized. The copolymerization parameters were determined: rVP = 0,61, rDMAEM = 11,41. The tacticity of DMAEM sequences and the distribution of monomer units were estimated. Then, the experimental conditions for the quaternization of the copolymers with alkyl bromides were defined. The modified copolymers were characterized and the mechanism of the quaternization reaction was studied via potentiometry.
Calorimetric study of blends of low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) temperature rising elution fractionation (TREF) fractions
Authors: Joskowicz Pablo L. , Muñoz Alberto , Barrera Julio , Müller Alejandro J.
Published: April 2003

Preparative temperature rising elution fractionation (TREF) on commercial linear low density polyethylene (LLDPE) and low density polyethylene (LDPE) samples has been performed. The resulting fractions exhibited a bimodal and a unimodal distribution, respectively. Two LLDPE fractions of low (5 CH3/1000 C) and high (21 CH3/1000 C) short‐chain branching content were solution‐mixed with the LDPE central fraction (16 CH3/1000 C). Indirect evidence based on differential scanning calorimetry results suggest that the fractions with similar branch contents are more miscible than those with dissimilar ones.
Synthesis and characterization of multiblock copolymers poly[poly(L‐lactide)‐block‐polydimethylsiloxane]
Authors: Bachari Abdelkrim , Bélorgey Georges , Hélary Gérard , Sauvet Georges
Published: April 2003

The preparation of multiblock copolymers poly[poly(L‐lactide)‐block‐polydimethylsiloxane] by polycondensation of bifunctional oligomers via hydrosilylation is described. The procedure consists first to synthesize the two bifunctional oligomers α,ω‐disilyl‐polydimethylsiloxane and α,ω‐diallyl‐poly(L‐lactide). The former is prepared in one step by cationic polymerization of octamethylcyclotetrasiloxane in the presence of 1,1,3,3‐tetramethyldisiloxane as end‐blocker. Two steps are necessary to prepare α,ω‐diallyl‐poly(L‐lactide). The first one is the polymerization of L‐lactide initiated by the system ethylene glycol/tin 2‐ethylhexanoate. In a second step, the hydroxyl end‐groups of the resulting α,ω‐dihydroxy‐poly(L‐lactide) are transformed, by reaction with allyl isocyanate, into terminal allylic functions. Different multiblock copolymers were prepared by hydrosilylation (catalyzed by hexachloroplatinic acid) using the same α,ω‐diallyl‐poly(L‐lactide) (M̄n = 2000 g · mol −1) and various α,ω‐disilyl‐polydimethylsiloxanes (M̄n from 1 750 to 9 000 g · mol −1). The influence of parameters such as temperature, stoichiometry of reactive end‐groups and catalyst concentration on the molecular weight of the copolymers was studied. High molecular weight copolymers were obtained (DPn > 12 by SEC). In addition to the biodegradability of the lactic acid units, the immiscibility of the polydimethylsiloxane and poly(L‐lactide) blocks imparts thermoplastic elastomer properties to these copolymers. The crystallinity of the poly(L‐lactide) phase is dependent on the molecular weight of the polydimethylsiloxane blocks.
A method for determining intrinsic diffusion coefficients in the pervaporation process
Authors: Walcher Tobias , Göritz Dietmar
Published: April 2003

An apparatus based on a differential gas‐chromatographic detection system was designed in order to obtain information about the average permeation coefficient for pervaporation (PVAP) of pure liquids through isotactic poly(propylene) (i‐PP). The non‐ideal concentration dependence of diffusivity D prevents one from solving the diffusion equations exactly. Therefore, a method has been developed to obtain information on the intrinsic diffusion coefficient D0 and the plasticisation parameter γ for the two‐parameter function D(c) used. In additon, the concentration profile of the liquid in the membrane can be evaluated.
Struktur der aktiven Spezies und Erklärung des Wanderungsmechanismus bei der 2,ω‐polymerisation von α‐olefinen
Authors: Schubbe Regine , Angermund Klaus , Fink Gerhard , Goddard Richard
Published: April 2003

The catalytic system nickel(0) compound and bis(trimethylsilyl)amino‐bis(trimethylsilylimino)‐phosphoran polymerizes α‐olefins via 2,ω‐linkage. Therefore this reaction is called 2,ω‐polymerization. Using tris(ethylene)nickel as the nickel compound in these systems, it is possible to obtain catalytically active species. The X‐ray analysis of these crystals proves that the nickel atom is complexed by one of the imino nitrogen atoms and fixed over a C2 bridge at the phosphorus atom. The unusual 5‐membered ring for complexes of this type gives a view into the mechanism of the 2, ω‐polymerization. The phosphorus ligand shields the nickel atom at which the insertion takes place so effectively that the nickel is practically sitting in a “cave” with a very small entrance. Inside the cave NiC reacts to NiH and CC and also in reverse: this means the enthalpy change is zero and it is a question of statistics (entropy) which C atoms of the double bond will be attacked. Varying the phosphorus compound demonstrates the high sensitivity of the catalytic system with respect to this compound. Substituting the trimethylsilyl groups at the imino nitrogen atoms by the more voluminous dimethyl‐tert‐butyl groups, we obtained an absolutely inactive system. In contrast, nickel(II)‐bis(acetylacetonate) can be used in combination with the phosphoran and aluminium triethyl as cocatalyst to obtain a catalytically active system for the 2,ω‐polymerization. The structure of this complex was identified by X‐ray analysis. Because of the higher volume of the ligand, this system is unable to polymerize branched α‐olefins; only linear α‐olefins will be polymerized via 2, ω‐linkage.
Propene polymerization in the presence of MgCl2‐supported Ziegler‐Natta catalysts, 5. Microstructural characterization of the “isotactic” (heptane‐insoluble) polypropene fractions
Authors: Busico Vincenzo , Cipullo Roberta , Corradini Paolo , De Biasio Rosanna
Published: April 2003

The stereosequence distribution in the heptane‐insoluble fraction of polypropene samples prepared with a number of MgCl2‐supported catalysts was analyzed in detail by means of 13CNMR. The results indicate that what is conventionally taken as “isotactic” polypropene is normally a stereoblock polymer, in which at least part of the macromolecules contain long isotactic blocks spaced by much shorter “syndiotactoid” sequences. This implies that the active sites responsible for the formation of the two types of stereosequences are able to interconvert reversibly on the surface of the MgCl2 support in times which may be shorter than the average growth times of the polymer molecules. Possible models of active sites apt to explain the observed polymerization behavior are also briefly discussed.
Phase equilibria and interfacial tension between coexisting phases for the system water/2‐propanol/poly(acrylic acid)
Authors: Tong Zhen , Meissner Kristin , Wolf B. A.
Published: April 2003

The cloud point curve, tie‐lines and interfacial tensions were measured for solutions of 50 mol‐% neutralized (counter‐ion Na⊕) poly(arylic acid) (mass‐average molar mass M̄w = 9700 g/mol; polydispersity index M̄w/M̄n = 2,0) in the mixed solvent water/2‐propanol at 30°C. Due to the non‐uniformity of the polymer, the end‐points of the tie‐lines are not situated on the cloud‐point curve. The interfacial tension σ — determined by means of the spinning drop method — increases in sigmoidal manner with Rtl, the length of the tie‐line, expressed in terms of weight fractions. An evaluation of these data in a double‐logarithmic plot of σ · M−0,5 versus Rtl yields a critical exponent of 4,23 as compared with 3,85 in the case of binary systems. The dependence of σ on ww, the over‐all weight fraction of water in the mixture, can also be expressed as a power‐law choosing (wcw−ww)/wcw as the concentration variable (wcw: critical weight fraction of water); for the present system the exponent of the resulting equation amounts to 2,33 as compared with 2,0 for toluene/polyisobutylene/poly(dimethylsiloxane).
Catalytic properties of enzymes modified with temperature‐responsive polymer chains
Authors: Nagayama Hitomi , Maeda Yasushi , Shimasaki Choichiro , Kitano Hiromi
Published: April 2003

Temperature‐responsive changes in catalytic properties of enzymes modified with a temperature‐responsive polymer, poly(N‐isopropylacrylamide) (PIPA), were examined. PIPA with a carboxyl group at its end was prepared using 2,2′‐azoisobutyronitrile as initiator in the presence of 3‐mercaptopropionic acid as a chain transfer reagent. After being activated by the coupling with N‐hydroxysuccinimide, PIPA was directly bound to enzymes such as acid phosphatase and trypsin. The catalytic activities of the modified enzymes showed a bending point in their Arrhenius plots at about 33°C due to a coil‐globule transition of PIPA chains. The ratio of amidase‐ and esterase‐activities of trypsin modified with PIPA chains was largely affected by the changes in temperature. As for the semi‐enzymatic synthesis of N‐benzoyl‐L‐arginylglycinamide, secondary hydrolysis of the peptide product observed with free trypsin was effectively suppressed in modified trypsin at 45°C (above the transition temperature), and the peptide was obtained with higher conversion.
The 1H and 13C NMR spectra of an alternating ethene/maleic anhydride copolymer and the corresponding acid and sodium salt
Authors: Komber Hartmut
Published: April 2003

The 1H and 13C NMR spectra of an alternating ethene/maleic anhydride copolymer and the corresponding acid and sodium salt were reinvestigated with regard to the signals depending on the configuration of the succinyl unit. From these assignments a 85/15 ratio of threo‐and erythro‐ succinyl configurations was determined. Threo‐ and erythro‐units are statistically distributed. Furthermore, signal splittings were observed due to microtacticity. Explanations are given for the signal fine structure. The polymer chain is atactic but a small degree of stereoregularity can be proved. T1 values and nuclear Overhauser effect (NOE) factors were determined; they correspond to investigations on other polymers.
Synthesis and characterization of novel triazeno‐group containing photopolymers
Authors: Nuyken Oskar , Stebani Jürgen , Lippert Thomas , Wokaun Alexander , Stasko Andrej
Published: April 2003

The synthesis of novel triazeno‐group containing photopolymers is described including their characterization by spectroscopic methods, differential scanning calorimetry, and thermogravimetric analysis. Triazene polymers synthesized by a polycondensation reaction between a bisdizaonium salt and a bifunctional secondary amine are well soluble in usual organic solvents. Transparent, light yellow films of these photopolymers may be produced by simple spin‐coating and solution‐casting techniques. The effect of polymer structural elements on the photolytic decomposition is studied. Depending on the structure of the polymer, thermolysis proceeds either via a one‐step or two‐step mechanism.
Synthesis and molecular weight characterization of end‐functionalized N‐vinyl‐2‐pyrrolidone oligomers
Authors: Ranucci Elisabetta , Spagnoli Gloria , Sartore Luciana , Bignotti Fabio , Ferruti Paolo , Schiavon Oddone , Caliceti Paolo , Veronese Francesco M.
Published: April 2003

New oligomers of N‐vinyl‐2‐pyrrolidone, functionalized at one end with hydroxy functions, were obtained by radical polymerization in the presence of a hydroxylated compound, namely 2‐isopropoxyethanol, acting as chain‐transfer agent. The oligomeric samples obtained were characterized in terms of molecular weight and molecular weight distribution by means of analytical size exclusion chromatography (SEC). To this purpose, a calibration curve for a set of SEC columns had been determined, making use of poly(N‐vinyl‐2‐pyrrolidone) standards purposely prepared. The chain transfer constant CT of 2‐isopropoxyethanol towards N‐vinyl‐2‐pyrrolidone was determined from the knowledge of the cumulated number‐average degree of polymerization X̄n and monomer conversion Yt of the samples during the reaction.
Synthesis and properties of molecularly uniform oligourethanes with chain‐folding units in the center
Authors: Eisenbach Claus D. , Stadler Edmund , Enkelmann Volker
Published: April 2003

The study of a series of molecularly uniform poly(N‐alkylurethanes) with a systematically varied and tailored chain architecture has shown that the packing and superstructure can be controlled by the primary structure of the urethane chain and reversibly altered by the sample treatment, respectively. Depending on the conformation or the stereogeometry of the constitutive unit built in the middle of the otherwise symmetrical oligourethane, chain‐extended and/or chain‐folded crystallization of the urethane chain can occur. The packing order, i. e., adjacent recentry chain‐folding or chain‐extended crystallization, and the thermal properties of the oligourethanes are related to the chemical structure of the central constitutive unit.
Free‐radical polymerization of acrylates α‐substituted by trimethylsiloxy substituents. Dramatic influence of the size of the ester substituent on the polymerizability
Authors: Penelle Jacques , Verraver Sandrine , Raucq Philippe , Marchand‐Brynaert Jacqueline
Published: April 2003

α‐Trimethylsiloxyacrylates H2CC(OSiMe3)COOR (R = methyl, ethyl, propyl, isopropyl, isobutyl, and trimethylsilyl) were synthesized and polymerized under free‐radical conditions. Despite the 1,1‐disubstitution by large substituents, all olefins were found to homopolymerize. Polymerizability is very dependent on the bulkiness of the ester substituent, the olefins with the largest ester groups being very reluctant to react. Polymerization of the methyl ester at 60°C was kinetically investigated. The rate dependence deviates from a first‐order kinetics with respect to monomer concentration (n = 1,81 (benzene solution) and 2,36 (DMF solution)), but follows the expected square‐root dependence with respect to the initiator (AIBN). A solvent dependence upon the rate of polymerization was also found. Copolymerization of the methyl ester (M1) with styrene (M2) was carried out at 60°C: r1 = 1,42, r2 = 0,46, Q = 0,47, and e = 0,04. Experimental results are rationalized on the basis of the steric hindrance introduced by the substituents and the high captodative stabilization of the propagating radicals.
Cholesterol‐containing non‐ionic amphiphilic polymers: synthesis and solubilization of cholesterol
Authors: Cho Iwhan , Jeong Sang Won
Published: April 2003

Solubilization of cholesterol in water with cholesterol‐containing poly(N‐vinyl‐2‐pyrrolidone) was studied. The non‐ionic amphiphilic polymers were synthesized via copolymerization of cholesterol‐based monomers with N‐vinyl‐2‐pyrrolidone; the copolymers were dissolved isotropically in water to form hydrophobic microdomains solubilizing cholesterol efficiently. Electron micrographs revealed that the amphiphilic polymers undergo aggregational changes from random microphases to bilayers as free cholesterol is incorporated into the polymeric hydrophobic domains.
Mise au point sur l'analyse par chromatographie par exclusion stérique en milieu aqueux de télomères de l'acide acrylique
Authors: Boutevin Bernard , Rigal Gérard , El Asri Mohammed , Lakhlifi Tahar
Published: April 2003

In the case of water soluble polymers, the use of size exclusion chromatography (SEC) for the determination of the molecular weight involves numerous difficulties. In order to analyse and determine the molecular weight of acrylic acid telomers we have first tried to obtain a satisfactory and reproducible separation. In this particular case, low‐molecular‐weight standards are not commercially available. Therefore, we decided to prepare standards based on acrylic acid, either by telomerization with a fluorinated telogen or by polymerization with an initiator bearing a fluorinated group. A calibration curve was obtained from the standards. Telomers of acrylic acid with thioglycolic acid were analysed. This is a general method for determination of DPn by SEC when there is no standard for the polymers. It can be used in a wide range of DPn from 1 to 700.
Polysilanes réactifs, 5. Optimisation de la synthèse des α,ω‐bis(triméthylsilyl)oligo (méthylphénylsilane)s par prise en considération d'un mécanisme anionique
Authors: Reyx Danièle , Martins José Manuel Natário , Campistron Irène , Noireaux Patrick
Published: April 2003

Low‐molecular‐weight organosilane polymers were prepared by sodium and potassium/sodium coupling of dichloromethylphenylsilane (1) with chlorotrimethylsilane (2). Size exclusion chromatography (SEC), IR, UV and NMR (1H, 13C and 29SI) analysis of the crude α,ω‐bis(trimethylsilyl) oligo(methylphenylsilane) (3) were performed and compared with those of the isolated shortest oligomers. According to an anionic mechanism, the solvent and alkali‐metal effects on the yield and the oligomer distribution (SEC‐resolved) allow an optimisation for the synthesis of the shortest oligomers (trisilane and tetrasilane).
Chain transfer by addition‐substitution mechanism, 4. Alkyl permethacrylates — a new class of polymerization regulators
Authors: Chaumont Philippe , Colombani Daniel
Published: April 2003

tert‐Butyl permethacrylate (tBPM)

Systematic names; t BPM: tert‐butyl peroxymethacrylate, CPM: α,α‐dimethylbenzyl peroxymethacrylate.

and cumyl permethacrylate (CPM)b act as chain transfer agents in the free radical polymerization of methyl methacrylate and styrene at 50°C. Thermal degradation of the peresters occurs as a side‐reaction during the polymerization process. A modified Mayo equation (including the first‐order decomposition of the chain transfer agents) is proposed to calculate the chain transfer constants. The thermolysis activation energy of CPM (Ea,th = 121 ± 5kJ/mol) was estimated from the Arrhenius plot of the homolytic decomposition rate constants, Kth' at various temperatures.
Styrene polymerization in methylene chloride by perchloric acid
Authors: Pepper David Charles
Published: April 2003

This paper makes a detailed reappraisal of earlier publications and much unpublished data on the polymerization by HClO4 over the temperature range 25°C to −97°C. The chief conclusions are: (i) The characteristic bimodal molar‐mass distributions found in polymers at temperatures down to about −30°C are not the result of intrinsic independence between propagating species, but of the intervention of irreversible transfer processes. (ii) The ‘common‐anion’ effect of added Bu4NClO4, on both the transient ionic concentration detectable at low temperatures, and on the yields and rates of polymerization, can be analysed to show the links between the rapid non‐equilibrium precursor phase and the subsequent steady phase. In that phase, the reactions are shown, by the number‐average molar mass (M̄n) of the polymer, to have the kinetic character of a ‘dormant‐living’ polymerization, near‐ideal at ca. −70°C, but deviating increasingly as transfer increases and finally dominates over the reversible termination process. (iii) That termination process is envisaged as ‘ion‐pair collapse’, the anion of the pair being ‘homoconjugated’ with a molecule of the acid, which is released on collapse. This mechanism, proposed by Szwarc, offers a satisfactory resolution of the ‘pseudo’ cationic controversy, interpreting the polymer ester molecules, not as propagating species, but as the reservoir from which propagating ion‐pairs are generated by acid‐activation.
Structure and reactivity of propagating species in anionic polymerization of 2‐vinylpyridine initiated by lithium derivatives in toluene
Authors: Hubert Philippe , Soum Alain , Fontanille Michel
Published: April 2003

A comprehensive kinetic study of the 2‐vinylpyridine living polymerization initiated by lithium derivatives in hydrocarbon solvents was carried out. Rate constants of propagation and thermo‐dynamic parameters were determined and discussed in relation to the structure of the propagating species. 13C NMR spectrometric measurements performed on a model of the living ends corroborate the conclusions derived from the values of kinetic and thermodynamic parameters.
A combined NMR and electron spin resonance investigation of the (C5(CH3)5)Ti(CH2C6H5)3/B(C6F5)3 catalytic system active in the syndiospecific styrene polymerization
Authors: Grassi Alfonso , Pellecchia Claudio , Oliva Leone , Laschi Franco
Published: April 2003

The reaction of (C5(CH3)5)Ti(CH2C6H5)3 with B(C6F5)3 in chlorobenzene at 25°C produces a mixture of [(C5(CH3)5)Ti(CH2C6H5)2]+ [B(CH2C6H5)(C6F5)3]− (1) and Ti(III) complexes which have been characterized by NMR and electron spin resonance (ESR) spectroscopy, respectively. Spectroscopic data combined with polymerisation activity measurements suggest that a Ti(III) complex is the active species in the styrene syndiospecific polymerisation.
A systematic approach to the study of multicomponent polymerization kinetics: the butyl acrylate/methyl methacrylate/vinyl acetate example, 2. Bulk (and solution) terpolymerization
Authors: Dubé Marc A. , Penlidis Alexander
Published: April 2003

A systematic study of the terpolymerization of butyl acrylate/methyl methacrylate/vinyl acetate (BA/MMA/VAc) is being conducted. In the second stage of this study, bulk (and solution) terpolymerizations of BA/MMA/VAc were performed. The polymers produced were characterized for conversion, composition and molecular weight. The terpolymerizations exhibited behaviour similar to vinyl acetate‐containing copolymerizations, that is, a “double gel effect” was observed. During the first period of the reaction the acrylic monomers virtually “copolymerized” and thus the reaction exhibited the characteristics of a “solution” copolymerization of the acrylic monomers with the vinyl acetate acting as the “solvent”. Typical “solution” polymerization behaviour, i. e., a dampened autoacceleration or gel effect, was in evidence for this first period of the reaction. After the virtual deplection of the acrylic monomers, the remaining vinyl acetate polymerized and exhibited its own characteristic gel effect. Estimates of the copolymerization reactivity ratios obtained previously were found to accurately predict terpolymer composition up to high conversion levels. Molecular weight results indicated that branched polymers were being produced at high conversions in the bulk experiments.
Well defined block copolymers of ε‐caprolactone and L‐lactide using Y5(μ‐O)(OiPr)13 as an initiator
Authors: Stevels Willem M. , Ankoné Marc J. K. , Dijkstra Pieter J. , Feijen Jan
Published: April 2003

Diblock copolymers composed of poly(ε‐caprolactone) and poly(L‐lactide) were synthesized via sequential living ring‐opening polymerization of ε‐caprolactone and L‐lactide in dichloromethane initiated by Y5(μ‐O)(OiPr)13 (yttrium isopropoxide). A series of diblock copolymers was synthesized with ε‐caprolactone blocks of constant length (DP = 70) and lactide blocks of varying length (DP = 5–80), with polydispersities of 1,18–1,27. Molecular weights were close to theoretical values. 13C NMR spectroscopy shows the absence of transesterification reactions and racemization. The thermal properties of the block copolymers were studied using differential scanning calorimetry. The block copolymers show a certain degree of phase mixing depending on the length of the poly(L‐lactide) blocks. Crystallization of L‐lactide sequences did not occur when the block length consisted of less than 40 L‐lactic acid residues.
Crystalline and disordered state of poly(dihexylsilylene) copolymers
Authors: Frey Holger , Möller Martin , Matyjaszewski Krzysztof , Oelfin Dieter
Published: April 2003

A systematic comparison of random copolymers, derived from poly(dihexylsilylene) (PDHS) by incorporation of monomeric units with shorter unbranched alkyl side chains, has been carried out based on calorimetry, variable temperature UV spectroscopy, and 29Si MAS (magic angle spinning) solid state NMR investigations. Also, hexylmethylsilylene units and branched monomers have been copolymerized. Up to 10% comonomer with shorter linear side chains (i. e., pentyl to propyl) could be incorporated into PDHS without impeding the all‐trans order of the crystalline phase. In this case, the UV absorption maximum of the crystalline low‐temperature phase was affected only slightly according to the length and fraction of the comonomer side chains. A less ordered crystal structure (λmax = 345–355 nm) was observed when the content of comonomers with shorter side chains was about 20%. Yet, all these materials form conformationally disordered mesophases. A clear disordering transition and corresponding thermochromism was not observed any more when 50% of propyl side chains were incorporated. The order of the crystalline and the mesophase is also strongly perturbed if only a small fraction (4%) of the side chains are branched at C2.
Hypochromism of poly(N‐vinylcarbazole)
Authors: Kowal Joanna
Published: April 2003

The hypochromy of poly(N‐vinylcarbazole) in relation to N‐ethylcarbazole was estimated for samples of different origin (cationic and radical polymerization). The effect of solvent polarizability and the influence of temperature as well as of the addition of nonsolvent were studied. An increase in hypochromy of the 1Lb transition and a decrease in that of the 1La transition with increasing polarizability of the solvent were observed. No change in hypochromy connected with increasing temperature and addition of nonsolvent was found.
Influence of the crown ether concentration and the addition of tert‐butyl alcohol on anionic polymerization of (butoxymethyl)oxirane initiated by potassium tert‐butoxide
Authors: Stolarzewicz Andrzej , Neugebauer Dorota , Grobelny Zbigniew
Published: April 2003

The influence of the crown ether concentration on the reaction rate constants and the equilibrium constant in anionic (butoxymethyl)oxirane polymerization was studied. Polymerizations of (phenoxymethyl)oxirane and (2‐(9‐carbazoyl)ethoxymethyl)oxirane were carried out for the sake of comparison. The observed changes caused by the addition of the crown ether can be related to both the structure of its complex with the counter‐ion and the structure of the monomer molecule. It was also revealed the tert‐butyl alcohol reduces the concentration of active centers and the molecular weight of the polymers.
Influence of the kind of crown ether on the anionic polymerization of (phenoxymethyl)oxirane initiated by potassium tert‐butoxide
Authors: Stolarzewicz Andrzej , Neugebauer Dorota , Grobelny Zbigniew
Published: April 2003

The propagation rate constant, kp, was determined for the polymerization of (phenoxymethyl)oxirane (2,3‐epoxypropyl phenyl ether) initiated by potassium tert‐butoxide in the presence of various crown ethers: 12‐crown‐4, 15‐crown‐5, 18‐crown‐6, dicyclothexano‐18‐crown‐6, dicyclohexano‐24‐crown‐8, dibenzo‐18‐crown‐6 and dibenzo‐24‐crown‐8. The equation correlating kp with complexation constants, Kc, of the crown ethers was derived.
Study of the microgelation of unsaturated polyester resins by dynamic light scattering
Authors: Liu S. B. , Yu T. L.
Published: April 2003

A series of unsaturated polyesters were synthesized with various chemical structures and molecular weights. The effects of molecular weight and degree of unsaturation on the curing reaction of these polyesters with styrene were studied by means of dynamic light scattering and differential scanning calorimetry. Two modes of size distribution of the microgel particles formed during the curing reaction were found from dynamic light scattering data. The small particles consist of primary unsaturated polyester molecules. The large ones consists of microgel particles formed by linking adjacent polyester molecules. The size and structure of the microgel particles depend strongly on the polymer chain length and the number of vinyl groups in each unsaturated polyester chain. The experimental results of this study revealed that microgel formation has a great effect on the curing reaction of unsaturated polyester resins.
Advances in polyelectrolyte research: counterion binding phenomena, dynamic processes, and the helix‐coil transition of DNA
Authors: Nordmeier Eckhard
Published: April 2003

The article gives a review about the actual stand on three fields of polyelectrolyte research. They are: counterion binding phenomena, dynamic processes, and the helix‐coil transition of DNA. The most important theories on each field are presented and their predictions are compared with the results of measurements. Various effects are handled in detail. They are: counterion condensation, counterion association, counterion binding in mixed solvents, polyion diffusion, and pressure effects on the melting temperature of DNA. The main purpose of the article is to show which effects are understood theoretically and which are not. Polyelectrolyte properties are sensitive to polyelectrolyte structure and environment. Therefore, a large number of parameters are varied over a wide range. They are: salt concentration, polyion charge, counterion valence, temperature, hydrostatic pressure, and solvent composition. Another intention is to bridge the gap between biological material research such as DNA and the physics and chemistry of synthetic polyelectrolytes and to plead for a closer cooperation between the two fascinating worlds.
Synthesis and liquid‐crystalline properties of thermotropic homopolycarbonates
Authors: De Backer Christel , Van Beylen Marcel , Ottenburgs Raoul , Samyn Celest
Published: April 2003

Six series of polycarbonates with flexible spacers have been prepared by melt condensation of aromatic diols such as 4,4′‐bis[(2‐hydroxyethyl)oxy]biphenyl, 4,4′‐bis [(6‐hydroxyhexyl)oxy]biphenyl, 1,5‐bis[(2‐hydroxyethyl)oxy]naphthalene, 1,5‐bis[(6‐hydroxyhexyl)oxy]naphthalene, 2,6‐bis[(2‐hydroxyethyl)oxy]naphthalene, 2,6‐bis[(6‐hydroxyhexyl)oxy]naphthalene, 4,4′‐bis[(6‐hydroxyhexyl)oxy]stilbene, 3,3′‐dimethyl‐4,4′‐bis[(2‐hydroxyethyl)oxy]stilbene, 3,3′‐dimethyl‐4,4′‐bis[(6‐hydroxyhexyl)oxy]stilbene, 4,4′‐bis[(2‐hydroxyethyl)oxy]‐α‐methylstilbene and 4,4′‐bis[(6‐hydroxyhexyl)oxy]‐α‐methylstilbene

For systematic IUPAC nomenclature see Experimental part.

with several alkylene diphenyl dicarbonates. Polycarbonates with biphenyl and stilbene mesogenic groups show liquid‐crystalline behavior with the formation of a nematic phase over a temperature range of 46°C and 21°C, respectively. Amorphous polycarbonates were obtained when 1,5‐naphthalene or α‐methylstilbene groups are incorporated. Polymers with 2,6‐naphthalene and 3,3′‐dimethylstilbene groups show mesophase formation up to a certain spacer length, a transition range of 15°C and 28°C, respectively, being observed.
Influence of lateral substituents in the mesogens on the properties of liquid‐crystalline side group copolymethacrylates: dielectric relaxation spectroscopy on homopolymers
Authors: Schönhals Andreas , Geßner Uwe , Rübner Joachim
Published: April 2003

Broad‐band dielectric spectroscopy in the frequency range from 10‐2 Hz to 106 Hz and in a temperature range from 170 K to 430 K was employed to study the molecular dynamics in polymethacrylates with novel calamitic side groups. As mesogenic units, derivatives of p‐methoxyphenyl benzoate were used where the hydrogen in the meta position of the benzoate ring is substituted by a methoxy group or by bromine. The substituted samples do not show any mesophases. The following results were obtained: (i) The β‐relaxation which corresponds to a rotational fluctuation of the mesogen around its long axis is drastically suppressed by the lateral substitution. Moreover the activation parameter of this process depends strongly on the actual mesophase structure of the material under study. (ii) The β‐relaxation is related to the dynamic glass transition of the system. It is shown that the value of the glass transition temperature of the liquid‐crystalline polymethacrylate can be understood as competition of internal plasticization and molecular ordering. (iii) The α‐relaxation corresponds to a rotational fluctuation of the side group around its short axis. From comparison of the relaxation rates of the α‐ and δ‐relaxation, the temperature dependence of the order parameter of the liquid‐crystalline polymethacrylate is estimated by dielectric spectroscopy.
Synthesis of end‐functionalized polymers by means of living anionic polymerization, 3. Synthesis of polystyrene and polyisoprene with 1,3‐butadienyl termini by reaction of their anionic living polymers with 6‐bromo‐3‐methylene‐1‐hexene
Authors: Takenaka Katsuhiko , Hirao Akira , Nakahama Seiichi
Published: April 2003

Both polystyrenes and polyisoprenes with 1,3‐butadienyl end‐groups were synthesized by the reactions of polystyryl and polyisoprenyl anions with 6‐bromo‐3‐methylene‐1‐hexene (3). The 1,3‐butadienyl end‐group was further transformed to an anhydride function by Diels‐Alder reaction with maleic anhydride. These end‐functionalized polymers were characterized by size exclusion chromatography (SEC), infrared spectroscopy, elemental analysis, 1H and 13C NMR, and thin layer chromatography coupled with a flame ionization detector. All analytical deta indicate that the polymers are quantitatively end‐functionalized with 3 and then with maleic anhydride. Polymers with one or two end‐functions are obtainable.
Effects of ortho‐substituents on the living polymerization of phenylacetylenes by MoOCl4‐based catalysts
Authors: Mizumoto Tomohiro , Masuda Toshio , Higashimura Toshinobu
Published: April 2003

Polymerization of phenylacetylenes (PAs) having various ortho‐substituents were examined by using MoOCl4—n‐Bu4Sn—EtOH (mole ratio 1:1:1) as catalyst. Phenylacetylenes with no or sterically small ortho‐substituents did not polymerize in a living fashion. On the other hand, in the polymerization of phenylacetylenes having medium‐sized substituents (e.g., CH3, Cl, Br, and iPr), the number‐average molecular weights Mn of polymers increased in direct proportion to monomer consumption, while the polydispersity ratios were 1,2– 1,3, which is in favor of living polymerization. Further, monomers having bulky ortho‐groups (CF3 and Me3Ge) exhibited excellent living nature with small polydispersity ratios of ≈ 1,1. Thus, it is concluded that not the electronic but the steric effect of the ortho‐substituent is important to achieve living polymerization.
A collagen‐polypyrrole hybrid: influence of 3‐butanesulfonate substitution
Authors: Li Hwee Chze , Khor Eugene
Published: April 2003

Hybrid biomaterials derived from a water‐soluble derivative of polypyrrole, poly(sodium 4‐(3‐pyrrolyl)butanesulfonate), and soluble collagen have been synthesized by chemical polymerization of the 4‐(3‐pyrrolyl)butanesulfonate monomer in a collagen solution. Interaction between the two polymers was evident in the formation of a precipitated black polymer‐collagen gel obtained for a monomer concentration of 0,01 mol/L. The collagen content in the gel was determined to be around 38 wt.‐%. When the monomer concentration was increased five‐fold, the product was a dispersed precipitate that was polymer rich with a corresponding decrease in collagen (11 wt.‐%) content. Fourier transform infrared spectroscopy and thermal analysis of the hybrids provide signs of interaction between the sulfonic acid group on the substituted pyrrole and side groups of amino acids in collagen. The electrical conductivities of these hybrid biomaterials were found to be in the 10−2 S. cm −1 range.
Interaction of slightly crosslinked gels of poly(diallyldimethylammonium bromide) with sodium dodecyl sulfate and cetylpyridinium bromide
Authors: Starodoubtzev Sergey G. , Minh Le Thi , Makhaeva Elena E. , Philippova Olga E. , Pieper Thomas G.
Published: April 2003

The interaction of slightly crosslinked gels of poly(diallyldimethylammonium bromide) (PDADMAB) with both the anionic surfactant sodium dodecyl sulfate (SDS) and the cationic surfactant cetylpyridinium bromide (CPB; system. name: N‐hexadecylpyridinium bromide) in aqueous medium has been investigated. The absorption of the anionic surfactant by the oppositely charged gel leads to contraction or collapse of the network. The absorption of the cationic surfactant by the gel‐SDS complexes results in a reswelling of the network. By means of IR and UV spectroscopy it has been shown that in the presence of the anionic detergent the cationic network absorbs the cationic surfactant. It has been shown that both reversible and irreversible complex formation in the gel phase is possible depending on the initial ratio between the components. Small‐angle‐X‐ray scattering experiments demonstrated that the complexes may have a regular microstructure.