摘要:

AbstractTotal solvent sorption and preferential adsorption by networks of poly(methylphenylsiloxane) (PMPS) and of poly(dimethylsiloxane) (PDMS) were determined in the mixture chloroform/diethyl ether. This liquid mixture has a negativeGE. The swelling degree of the networks was found to vary linearly with mixed solvent composition (Cl3CH volume fraction ϕ), contrary to what is expected in view ofGE<0. The preferential adsorption by PDMS shows an inversion which is of the divergent type (preferential adsorption of the liquid in major proportion in the mixture). With PMPS no inversion was observed, Cl3CH is always preferentially adsorbed, but the trend is also divergent (with the inversion point displaced to ϕ Cl 3CH= 0). The unexpected behaviour of the swelling degree and the displacement of the inversion in preferential adsorption are attributed to strong attractive interactions of the siloxane backbone with the two solvents, and of phenyl groups (in PMPS) with Cl3CH. The intrinsic viscosity of linear PMPS at infinite dilution was determined in the same mixed solvent, in order to check the possible influence of the polymer concentration. Comparison with network swelling shows a similar beha

ISSN:0025-116X    

DOI:10.1002/macp.1988.021890201

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractA polysaccharide macroinitiator (M̄n= 5000 to 28000) (1), having a reactive chlorine atom at the reducing end, was prepared by ring‐opening polymerization of 1,6‐anhydro‐2,3,4‐tri‐O‐benzyl‐β‐D‐glucose (TBLG) with antimony pentachloride as initiator in presence of acetyl chloride in dichloromethane at −60°C. Macroinitiator1in combination with silver hexafluoroantimonate was found to induce the polymerization of 6,8‐dioxabicyclo[3.2.1]octane (DBO) in tetrahydrofuran, 2‐methyltetrahydrofuran, or tetrahydropyran at −78 to 0°C. Fractionation of the reaction products gave a block copolymer (2) composed of poly(TBLG) and poly(DBO) segments. Debenzylation of2provided an amphiphilic block copolymer (3) consisting of hydrophilic (1→6)‐α‐D‐glucopyranan (dextran) and hydrophobic poly(DBO) [(1→6)‐linked polysaccharide skeleton] segments. Block copolymer3is soluble in dimethyl su

ISSN:0025-116X    

DOI:10.1002/macp.1988.021890202

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe photo‐crosslinking of polymers containing pendant epoxy groups was carried out at room temp. in the presence of a photosensitive sulfonium salt which is an initiator of cationic polymerization. The crosslinking reactivity of the epoxide‐containing polymers was found to depend on the mobilities of both the backbone of the polymers and the pendant epoxy groups, and on the epoxide structure. The introduction of spacer chains between the polymer backbone and the epoxy groups increases the mobilities of the backbone and the epoxides, resulting in an increases crosslinking reactivity. The introduction of a methyl group at the epoxy ring of the polymers with glass transition temp. (Tg) lower than room temp. enhances the crosslinking reactivity, whereas it diminishes the reactivity for the polymers withTghigher than room temp. This result can be explained by assuming that the presence of the methyl group results not only in an increase of the epoxide reactivity due to both the inductive effect of the methyl group and the increased ring strain, but also the decreased mobility of the epoxy groups. Thus, the reactivity of the rubbery polymers is principally controlled by the intrinsic reactivity of the epoxides, and the reactivity of the rigid polymers is mainly controlled by the mobility of the reactive si

ISSN:0025-116X    

DOI:10.1002/macp.1988.021890203

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractUnsaturated spiroorthoesters, which undergo no shrinkage on polymerization, were synthesized in high yield by an elimination reaction of the corresponding halomethylated spiroorthoesters with potassium hydroxide (KOH) or potassiumtert‐butoxide (t‐BuOK) using a phase transfer catalyst. It was found that tetrabutylammonium bromide exhibits a catalytic activity higher than that of the other quaternary ammonium salts, 18‐crown‐6 and poly(ethylene glycol) (M̄w= 300) under equal conditions. The elimination reaction of halomethylated spiroorthoesters proceeds easily in toluene or diglyme with t‐BuOK and intert‐butyl alcohol with KOH leading to the corresponding unsaturated compounds in high yields. In addition, the bromomethylated spiroorthoesters showed higher reactivity than the chloromethylated spiroorthoesters under equa

ISSN:0025-116X    

DOI:10.1002/macp.1988.021890204

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractUnliving chains of aliphatic polyester were transformed into dicationically living poly(THF)‐block‐polyester‐block‐poly(THF) chains, and four different telechelic triblock co‐oligomers with primary, secondary, tertiary amine, and hydroxyl end‐groups were synthesized. A novel approach to the exchange of hydroxyl or carbonyl ends of polyester for amino end‐groups is described. The primary amine‐terminated telechelic triblock was used to modify an epoxy resin to give a toughened product wit

ISSN:0025-116X    

DOI:10.1002/macp.1988.021890205

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractNegatively charged lipid molecules were converted into polymerizable lipids by introduction of polymerizable mono‐ or bifunctional counterions. As an attempt to mimic the cytoskeleton of biomembranes, unsymmetrical polymeric vesicles were prepared, where the polyelectrolyte is attached either only to the inner or to the outer bilayer surfaces. Polymerizable cations were introduced to the outer surface of preformed small unilamellar vesicles via ion‐exchange. The outer counterions of vesicles bearing polymerizable counterions at both sides of the membrane were replaced by Na+. Polymerization of these systems leads to unsymmetrical vesicles. The introduction, separation and polymerization of the organic counterions was monitored by UV‐spectroscopy. Due to polymerization of the counterions, the phase transition temperature of the membranes is shifted remarkably to higher temperatures. For a comparison of ionically attached and covalently bound polymers, two cationic lipids were synthesized, which have a bifunctional polymerizable headgroup. In contrast to the lipids with “ionic” spacers, the polymerization of the covalently bound methacrylic units resulted in a decrease of the phase transition temperature. Thus, by application of ionically bound polymerizable units, unsymmetrical polymerized vesicle membranes are readily available. These systems may serve as models for mimicking the cytoskeleton of liv

ISSN:0025-116X    

DOI:10.1002/macp.1988.021890206

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

Abstractδ Valerolactone and ϵ‐caprolactone were reacted with BBr3, AIBr3, TiBr4, SnBr4or Bu2SnBr2in dichloromethane or chloroform in a 1 : 1 mole ratio. When these exothermic reactions were conducted with cooling, complexation of the lactones at the exocyclic oxygen was detectable by means of IR and1H NMR spectroscopy as the first reaction step. However, heating to 60°C causes in all cases ring cleavage, and after hydrolytic removal of the metal bromides ω‐bromocarboxylic acids or oligomers with ω‐bromoalkanoyl end groups were obtained. SnBr4, Bu2SnBr2and ZnBr2proved to be good initiators of the polymerization of both lactones. At low monomer/initiator (M/I)‐ratios (high initiator concentrations) most of the initiator remained unchanged, and the average degrees of polymerization of the resulting polylactones largely exceeded the value expected for the M/I‐ratio. By means of viscosity and GPC measurements weight‐average molecular weights up to 70 000 were found. All polylactones obtained by initiation with these three metal bromides contain ϵ‐bromoalkanoyl end groups. Furthermore, high‐molecular‐weight poly(ϵ‐caprolactone) could be prepared at polymerization temperatures up to 150°C. The results do not indicate a cationic polymerization mechanism, but an insertion mechanism involving the metal‐O bond formed after the first

ISSN:0025-116X    

DOI:10.1002/macp.1988.021890207

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe factors relating to measuring the position of the methyl deformation mode at about 1378 cm−1with sufficient precision to permit its use for the identification of the different branches present in the various types of “linear” low density polyethylene(as manufactured by the copolymerization of ethylene and a 1‐alkene) have been examined systematically. With a data density of eight points per wavenumber, and the well established subtraction procedure with polymethylene or with a near‐linear polyethylene to remove the overlapping methylene deformation band, it is possible to achieve a precision of ±0,15 cm−1. This is ample to distinguish between methyl, ethyl, and butyl or hexyl branches, but not to characterise uniquely these last two. The use of Fourier self‐deconvolution to separate the methyl band has also proved very effective. The precision obtainable when these methods are applied to spectra measured with one data point per wavenumber is somewhat lower, but is still adequate for characterisational purposes. The results for a series of polymers containing ethyl branches at various concentrations suggest a small difference for the peak position for branches present in crystalline and amo

ISSN:0025-116X    

DOI:10.1002/macp.1988.021890208

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe emulsion copolymerization of acrylonitrile and butyl acrylate initiated by potassium peroxodisulfate (K2S2O8) in the presence of an anionic, cationic, or nonionic emulsifier has been kinetically investigated at 60°C under batch conditions by gas chromatography (GLC) and gravimetric methods. It is found convenient to define three stages of emulsion polymerization. In the range of low conversion (interval 1) are generated particles and the rate of polymerization increases with increasing polymer particle concentration. In interval2(ca. from 15 to 70% conversion) the number of polymer particles and the rate of polymerization (maximum) are constant. At very high conversion (above ca. 70% conversion) the monomer concentration within polymer particles decreases abruptly and the polymerization rate slows down (interval 3). The rate of polymerization in interval2was found to be proportional to the 0,41, 0,48, and −0,42 power of the emulsifier concentration for the anionic, nonionic, and cationic emulsifier, respectively. The dependence of the final particle number on the emulsifier concentration deviates from simple micellar theory predictions. The exponent of the emulsifier concentration decreases with increasing emulsifier concentration (for the anionic and nonionic emulsifiers). These results were explained by a coagulative nucleation mechanism. The unexpected polymerization behaviour in the presence of the cationic emulsifier was explained by the formation of a product (due to interaction of the initiator with the emulsifie

ISSN:0025-116X    

DOI:10.1002/macp.1988.021890209

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe intrisic viscosity [η] of poly(vinyl alcohol) (PVA) was determined in aqueous solutions with various concentrationscbof borax (Na2B4O7) as functions of molecular weightMand concentrationcsof NaCl as an added salt. Polyelectrolyte viscosity behaviour was observed for the systems containing both borax and NaCl, due to the complexation with negatively charged borate ions B(OH)−4· [η] changes depending on the ionic strengthI. It was found that the Stock‐mayer‐Fixman treatment for the molecular‐weight dependence of [η] is valid in the lower molecular‐weight range (M<105), even though the present PVA chain contains some intrachain crosslinks. Theta conditions can be attained at an appropriate concentrationcs Θof NaCl. The value ofcs Θis dependent oncb, but the conformational parameter from the Stockmayer‐Fixman treatmentK0is almost independent ofcb. The effect of intrachain crosslinks becomes evident only as a considerably large negative value for the excluded volume parameterBat infinite ionic strength. In addition, the electrostatic part of the expansion factor α 3ewas found to be linearly correlated to a reduced parameter (M/I)1/2for allcbsystems, from the slope of which the charge d

ISSN:0025-116X    

DOI:10.1002/macp.1988.021890210

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY