摘要:

AbstractSynthetic poly(alkylene phosphate)s with repeating units constituted of five or six atoms, i.e., (CH2)nOP(O)(OH)O‐, where n=2 or 3, mimick backbones of biopolymers: nucleic acids. (NA) and teichoic acids (TA). Progress in the synthesis of these polymers is briefly reviewed. The newly developed synthesis of ionic gels, based on reaction of H3PO4with diepoxides, leads to products with repeating units of TA. These highly water swellable gels slowly hydrolyse at the triester knots, and convert into linear poly(alkylene phosphate)s, stable in water (containing only hydrolytically stable mono‐ and diester units). Polymers modeling TA, poly(1,2‐glycerol phosphate) and its acetate as well as poly(trimethylene phosphate) were studied in the ion transport processes ‐ one of the basic functions of TA, major component in membranes of cell walls of Gram‐positive bacteria. Transport of Mg2+and Ca2+ions is analysed, and dependence of the ratio of fluxes of these ions with poly(alkylene phosphate) liquid membranes on the structure of the polymer used is

ISSN:0258-0322    

DOI:10.1002/masy.19910480104

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractStiff macromolecules are obtained by combining two aromatic units, either directly or by vinylene or ethynylene. The palladium‐catalyzed synthesis of poly(1,4‐phenylenevinylene), poly(1,4‐phenyleneethynylene), and poly‐p‐phenylene is described. Side reactions influencing the rodlike structure are investigated by model reactions.Phenyl‐substituted poly‐p‐phenylene is obtained starting from phenyl‐1,4‐dibromobenzene. This is a solution and melt processable polymer that is stable up to 600°C. By anionic polymerization of 2‐phenyl‐1,3‐cyclohexadiene a precursor polymer with Mw/Mn= 1,1 can be obtained with molecular weights up to 30 000. By aromatization, poly(phenyl‐1,4‐phenylene) with a narrow molecular weight distribution is obtained. All of these polymers show thermotropic behaviour.Poly(1,4‐pyridinium salts) are a new class of polymers. They are rodlike polycations. With large gegenions they

ISSN:0258-0322    

DOI:10.1002/masy.19910480105

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractOur study has been focused on the fast anionic polymerization of ϵ‐caprolactam (CL) under isothermal conditions, both in bulk and in suspension, in the temperature range between 150 and 200°C.A careful choice of the reaction parameters (type and concentration of activator, polymerization temperature and rate, cooling rate after polymerization) enabled us to find experimental conditions suitable for minimizing the extent of side reactions and, consequently, the concentration of UV‐absorbing structures incorporated in the poly(ϵ‐caprolactam) (PCL) chain. In terms of structural regularity, the resultant PCL compares favorably to the corresponding polyamide synthesized by the hydrolytic process. Moreover, extension of this approach to the anionic polymerization of CL in suspension allowed us to obtain particulated PCL, characterized by controlled size and surface porosity. Several PCL‐based materials, formed by seeded suspension polymerization, have been obtained. Potentials of this new synthetic approach ar

ISSN:0258-0322    

DOI:10.1002/masy.19910480106

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractA series of narrow distribution ω‐functionalized linear polyisoprenes were prepared by converting the tertiary amine group of polyisoprene ‐ obtained by anionic polymerization of isoprene with 3‐(dimethylamino)propyl lithium ‐ to the highly polar sulfo‐zwitterion group by treatment with cyclopropane sultone. The dilute solution properties of these polymers were mainly examined in cyclohexane and cyclohexane/1‐heptanol mixtures. In cyclohexane the sulfo‐zwitterion polymers were highly aggregated. The degree of association generally decreases with increasing base chain length, due to excluded volume repulsions of the polymeric tails, except at very low molecular weights (2 400–4 800) where the different microstructure of these polymers may play a role. Depending on the molecular weight of the linear precursor, the aggregates may resemble star polymers or may exhibit a more extended core morphology. These findings, regarding the shape of the aggregates, are also supported by melt viscosity mesurements and x‐ray

ISSN:0258-0322    

DOI:10.1002/masy.19910480107

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractBlends with random or block copolymers are discussed, where all components are made of one or both monomers of a given monomer pair. The critical copolymer compositions of blends of two random copolymers were determined, and phase morphologies were studied in blends close to and far from the critical point. Further, the tensile strength of blends of varying compatibility was tested. Microphase and macrophase structures of blends with one or two homopolymers and a symmetric block copolymer were characterized as a function of the chain length ratio of the components. Experiments were compared with model calculations.

ISSN:0258-0322    

DOI:10.1002/masy.19910480108

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractA review of the polyamide poly(α‐isobutyl‐L‐aspartate), embracing synthesis, crystal structure and properties, is reported. The interest in this nylon‐3 derivative arises from its ability to adopt conformations similar to the characteristic α‐helix of polypeptides. Two different synthetic approaches, both of them starting from L‐aspartic acid, have been followed for the preparation of this polyamide. Poly‐condensation in solution of α‐isobutyl‐L‐aspartate pentachlorophenyl ester yielded polymers with molecular weights up to near 80 000. About six times higher values were obtained by anionic polymerization of β‐lactam of α‐isobutyl‐L‐aspartate. Highly regular chains were attained in both cases. Two crystalline forms, hexagonal and tetragonal, made of helices with 3.25 and 4 residues per turn, respectively, were characterized by X‐rays and electron microscopy. Transitions between these two forms in the solid state were induced by heating, whereas a helix‐coil conversion promoted by acids was found to take place in solution. Liquid crystal properties have been observed for solutions of this polymer in helicogenic solvents, and films with cholesteric structure were spontaneously generated from them by casting. On the contrary, uniaxially oriented films could be obtained when cast under the effect of an electric field. A shear piezoelectric response of about 12

ISSN:0258-0322    

DOI:10.1002/masy.19910480109

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractWorks on strictly uniform ultra‐long n‐alkanes enabled the exploration of the onset of chain folding with increasing molecular length. It was established that folding sets in beyond a certain chain length, more specifically dependant on crystallization temperature (Tc), starting in an initially irregular chain deposition, reorganizing subsequently into a strictly quantized conformation of integral fractional fold lengths through either thickening or thinning of the crystal. In the final reorganized stage the folds are regular and sharp. The isothermal crystallization rates for extended chain crystals were found to go through a maximum followed by a minimum with decreasing Tcwhere chain folding takes over. This remarkable rate inversion, observed for C246H494and C198H398, so far, occurs both for solution and melt crystallization and could be verified for both primary nucleation and crystal growth. We interpret it in terms of a “self poisoning” phenomenon, where chain depositions, which occur transiently in the “wrong” conformation, are blocking the nucleation and growth of the crystal, a phenomenon also reflected in the reversal of the temperature dependence of isothermal refolding on crystallization from solution. Rate reversals of all these kinds promise to be basic to our understanding and are giving rise to recent alternative explanations from elsewhere which are being quoted an

ISSN:0258-0322    

DOI:10.1002/masy.19910480110

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractStudies of crystallization of polyethylene (sharp fractions) under hydrostatic pressure revealed that the previously identified mobile hexagonal phase (h) can arise as a metastable transient even in the more customary orthorhombic (o) stability regime. In fact, it was found that crystallization in thehphase controls the crystallization process even there, at least in the portion of the P‐T phase diagram explored so far. Accordingly, crystallization (nucleation and growth) can only take place while in thehphase and ceases upon transformation into theophase (occurring when theophase is the stable one). Crystal growth includes both lateral and thickening growth. Thickening growth in particular involves chain refolding, envisaged by sliding diffusion, and can proceed to thicknesses far in excess to chain extension. All growth rates can be defined quantitatively and correlated with morphology. The above findings are raising wider issues such as: Are metastable transients necessary for polymer crystallization underallconditions, or alternatively are there at least two different modes of crystallization with a change‐over unspecifiable by thermodynamics? Beyond this it raises the possibility of a new source for finite uniform lamellar thickness in the form of crystal‐thickening‐induced growth limiting phase inversion, an example for which has already been found in polymer trans‐1,4‐po

ISSN:0258-0322    

DOI:10.1002/masy.19910480111

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractInternal viscosity, or the high‐frequency viscous dissipation in polymer dynamics originating from the rotational energy barriers around skeletal bonds, is basically attributed to hindrance against the motion of conformational changes along the chain contour. The non‐equilibrium statistical‐mechanical background of the theory is discussed. Comparison between calculations and experimental results of the complex modulus and of the optical flow birefringence from polystyrene solutions under alternating shear stress is discussed. The best‐fitting value of the characteristic time for bond rotation τ0, i.e., the only parameter required for internal viscosity, is in good agreement with the results of NMR, ESR and dielectric relaxation exp

ISSN:0258-0322    

DOI:10.1002/masy.19910480112

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe segmental dynamics inside a polymer chain is described at first by considering the types of motions which can be performed and the corresponding motional models. Fluorescence Anisotropy Decay and Nuclear Magnetic Relaxation are two very convenient techniques. Results obtained on a series of polymers with low Tg's are presented and discussed. Local motions in solid polymeric materials and their influence on mechanical properties (viscoelasticity, modulus and plastic deformation) are illustrated in the case of model epoxy resins.

ISSN:0258-0322    

DOI:10.1002/masy.19910480113

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY