摘要:

AbstractWe present results on the effect of the cross‐linking density on the collapse of poly‐(methacrylic acid) gels induced by the interaction with linear poly(ethylene glycol) and on their subsequent reswelling (reentrant transition). The abruptness and the amplitude of both transitions increase with decreasing cross‐linking density of the gel. A special feature of the reswelling transition for the PMAA gel/PEG system is the existence of a wide range of PEG concentrations where both collapsed and swollen states of the gel are stable. The conditions for the existence of such a region are easier realized for slightly cross‐linked gels. The corresponding theoretical explanation is given. The swelling degree of the collapsed gels increases with increasing cross‐linking density, which is explained by the presence of a certain amount of hydrophilic PEG loops in highly cross‐

ISSN:1022-1352    

DOI:10.1002/macp.1996.021970801

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe anionic ring‐opening polymerization of a model monomer of cyclodisilazanes1, initiated with both organosodium and organolithium initiators, was investigated. Under specific conditions, this polymerization exhibits all the characteristics of a living process. Indeed, whatever the experimental conditions chosen, there is no evidence of back‐biting and/or transfer reactions competing with the propagation reaction. Kinetic measurements showed that this polymerization is first order with respect to the concentrations of both monmer and active centers. The absolute rate constant of propagation (kp) and the thermodynamic parameters (enthalpy and entropy) of the propagation step where calculated. On the basis of these results, a mechanism of the anionic ring‐opening polymerization of1is pro

ISSN:1022-1352    

DOI:10.1002/macp.1996.021970802

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractPoly(2,5‐dipropargyloxy‐1,4‐phenylenevinylene) (PDPPV) and its copolymers were prepared as thin films via the organic‐soluble and water‐soluble precursor routes. Elimination and crosslinking reactions could be controlled by the temperature. Crosslinked PDPPV is stable up to 450°C. The conductivity values of undrawn and drawn FeCl3‐doped PDPPV films are 5.0 × 10−2and 2.0 × 10−1Sċcm−1, respectively. The third‐order nonlinear optical susceptibility, χ(3), for the PDPPV film was investigated by degenerate four‐wave mixing (DFWM) technique at 602 nm wavelength, and

ISSN:1022-1352    

DOI:10.1002/macp.1996.021970803

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractN‐(3‐Dimethylaminopropyl) acrylamide (DMAPAA) andN‐(3‐dimethylaminopropyl) methacrylamide (DMAPMA) were prepared and polymers with pendant amino groups were synthesized via copolymerization of methyl methacrylate (MMA) with DMAPMA. With benzophenone (BP) as a sensitizer, the photo‐grafting reaction of acrylonitrile (AN) onto poly(MMA‐co‐DMAPMA) was investigated. The formation of a graft copolymer is confirmed by means of IR spectroscopy, elemental analysis and viscometry. The photoreaction of BP with polymers having pendant amino groups was studied by means of electron paramagnetic resonance (EPR) spectroscopy. It revealed that an alkylaminomethylene radical and a semipinacol radical are produced by the photoreaction. Amino end‐group analysis also proved that the radical formed from the amino component can initiate radical polymerization. Based on the EPR studies and amino end group analysis, the photo‐grafting reaction mech

ISSN:1022-1352    

DOI:10.1002/macp.1996.021970804

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractAnilino‐terminated poly(m‐phenylene isophthalamide) [PhNH(MPD‐I)] and benzoyl terminated poly(p‐benzamide) [PhCO(PBA)] were coupled according to a one‐pot two‐step scheme of Yamazaki's reaction. Diblock copolymers with varying length of the flexible PhNH(MPD‐I) segment, and similar length of the rigid PhCO(PBA) block, were freed from unbound homopolymers exploiting their selective solubility inN,N‐dimethylacetamide (DMAc) containing varying amounts of LiCl. The method should also allow a fractionation of the compositional distribution of the copolymers. Copolymers were characterized by1H NMR spectroscopy, thermal analysis and intrinsic viscosity. In an aggregating solvent the viscosity appears todecreasewith the length of the

ISSN:1022-1352    

DOI:10.1002/macp.1996.021970805

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractIn order to prepare the soap‐free emulsion of urethane acrylates, poly(ethylene glycol)‐modified urethane acrylates (PMUA), containing poly(oxyethylene) chains as terminal groups, were synthesized by reaction of poly(ethylene glycol) (PEG) with residual isocyanate groups. The size of the droplets of PMUA emulsions decreases as the molar ratio of PEG to 2‐hydroxyethyl methacrylate (2‐HEMA) increases. The interfacial activity of PMUA was confirmed by the measurement of the adsorption isotherm at the water/benzene interface. The chain length of poly(oxyethylene) and the type of polyol (PTMG, PPG) affects significantly the size of the droplets and the stability of the PMUA em

ISSN:1022-1352    

DOI:10.1002/macp.1996.021970806

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractA novel germanium‐containing copolymer3 ahaving a germanium(IV) unit and a trimethylene sulfide unit alternatingly in the main chain was prepared by the combined use of a germylene, 1,3‐bis(trimethylsilyl)‐1,3‐diaza‐2‐germa(II)‐indan (1 a) and thietane (2). The resulting copolymer has a very high molecular weight (M̄w>106). The usage of a germylene, bis[bis(trimethylsilyl)aminato]germanium(II) (1 b), as a comonomer also gave an alternating copolymer3 bwith high molecular weight in good yields. On the other hand, the reaction of a germylene, bis(N‐trimethylsilyl‐tert‐butylaminato)germanium(II) (c), with thietane afforded a 1 : 1 adduct4chaving a 1‐thia‐2‐germacyclopentane structure without producin

ISSN:1022-1352    

DOI:10.1002/macp.1996.021970807

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractA series of poly(ethyl acrylate)/polystyrene composite emulsions with different compositions and levels of emulsifier was produced by seed emulsion polymerization. The morphology of the composite particles was inferred from their coalescence ability detected by torsional braid analysis. It was found that the poly(ethyl acrylate) will partially move to the exterior of the particles when using it as a seed, and the increase of surface tension of the particles can enhance this diffusion.

ISSN:1022-1352    

DOI:10.1002/macp.1996.021970808

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

Abstract2‐Isopropenyl‐4‐methylene‐1,3‐dioxolane (1) undergoes cationic polymerization in donative solvents without crosslinking to afford poly(ether‐ketone)2having two unitstructures. When solvents having medium donor number (DN = 14,1–17,1), such as acetonitrile, dioxane, ethyl acetate, and propylene carbonate, were used,2was obtained in high yields. When solvents having DN (>19,2), such as diethyl ether, DMF, and DMAc, were used, the rate of polymerization decreased considerably, although polymerization proceeded even in the most donative solvent, DMAc (DN = 27,8). The ratio of the unit‐structures was independent of the solvent used. When ethanol was used as the solvent, ethoxyacetone and methacrolein were obtained instead of2. It was concluded that hard nucleophiles such as ethanol attack at the α′‐position of terminal oxyallyl cation, while soft nucleophiles such as monomer1attack at

ISSN:1022-1352    

DOI:10.1002/macp.1996.021970809

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe liquid crystallinity of poly(ester‐imide)s obtained from biphenyl‐4,4′‐diol, ω‐amino acids and trimellitic anhydride is discussed. Four models1–4, similar to repeating unitsI–III, were prepared from biphenyl‐4,4′‐diol or biphenyl‐4‐ol and 6‐phthalimido‐hexanoic acid, 6‐(4‐carboxyphthalimido)hexanoic acid andN‐hexyltrimellitimide. DSC and microscopic studies revealed that only biphenyl groups esterified with two aromatic acids are thermotropic, and those parts of the chain pr

ISSN:1022-1352    

DOI:10.1002/macp.1996.021970810

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY