1993 рік

A new ionic diol, the monosodium salt of fl-glycerophosphoric acid, was synthesized. The commercially available disodium salt was first converted to the fl-glycerophosphoric acid which was then neutralized with the requisite amount of sodium hydroxide to yield the monosodium salt of the acid. The monosodium salt was soluble in DMSO, in contrast to the disodium salt, which was found to be insoluble in almost all solvents with the exception of water. The monosodium salt of glycerophosphoric acid (GPA-Na) was used subsequently as a chain extender diol in the two-step synthesis of polyurethane ionomers using also butane-l,4-diol, polypropylene glycol and diphenylmethane-4,4'-diisocyanate. The reaction was catalysed by using a trace of dibutyl tin dilaurate. Both the ionic diol and the polyurethane ionomers were characterized using FTi.r., 1H n.m.r, and 31p n.m.r. Differential scanning calorimetry was also performed using these polymers.

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The model presented here to describe the deformation behaviour of filled elastomers is based on the observation that deformation occurs inhomogeneously. As a result of extending a filled rubber, the filler particles become aligned in rows parallel to the stretching direction. The rows are connected to each other by strands emanating from the filler particles, forming a second network that is superimposed on the molecular network. The stress-strain behaviour can be described by writing the stress as a superposition of stresses of the individual networks, a=(1-O)al +~a2. The parameter • gives the volume fraction of strands between the filler particles. Macroscopic properties such as stress-strain behaviour or stress-induced crystallization of filled elastomers are described well by this model.

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Irradiated polymers such as polystyrene (PS), poly(methyl methacrylate) (PMMA) and poly(~-methylstyrene) (PoeMS) have been studied using size exclusion chromatography and double-modulation electron spin resonance (d.m.e.s.r.). Size exclusion chromatography coupled on-line with low-angle laser light scattering and viscometry have demonstrated that PS irradiated in the solid state gives only slight increases of molecular weight and viscosity with increasing dose. When irradiated in solution, the results confirm the existence of a highly crosslinked and heterogeneous PS matrix. PMMA and P~MS undergo degradation at the same doses. The d.m.e.s.r, spectra of a spin probe in the slow-motion region have been used to investigate the heterogeneity of the polymer matrix introduced by changes in crosslinking or by degradation. Discrete molecular motions of a spin probe above the internal probe transition (g 190 K) are very sensitive to local matrix density and to side-chain relaxation modes. The d.m.e.s.r, spectra indicate clearly a bimodal motion of spin probes located in regions of two considerably different crosslink densities of the PS matrix irradiated in solution.

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Segmented block copolymers (SBCs) based on poly(butylene terephthalate) (PBT) and telechelics based on dimerized fatty acids have been synthesized in the melt. The dimerized fatty acids were coupled with diols or diamines to synthesize polyesters and polyamides of low molar mass. With these telechelic polyesters and polyamides we studied the influence of the different types of blocks and the block length on thermal transitions with differential scanning calorimetry and dynamic mechanical thermal analysis. The melting behaviour was compared to an SBC based on a dimerized fatty acid (Mn = 565 g mol- 1) and PBT. Neither the compositions of the SBCs nor the block lengths of the telechelic polyesters and polyamides seemed to be of influence on the melting behaviour. The glass transition temperatures (Tg values) of the SBCs based on the telechelic polyester decreased, while the Tg of the SBC based on the primary polyamide increased. Higher reaction temperatures and longer reaction times increased Tg, owing to transesterification reactions in the melt.

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In contrast to some thermoplastics, in which weld strengths equal to those of the base resins can be achieved, tests on two grades of acrylonitrile-butadiene-styrene resin (ABS) show weld strengths on the order of 90-95% of the strength of ABS, with slightly higher values being obtained at lower rubber levels. Welds of ABS to four other thermoplastics are shown to have strengths in the range of 65-83% of the strength of ABS, the weakest of the five thermoplastics. The welding of ABS to bisphenol-A polycarbonate is examined in detail. Optical, scanning and transmission electron microscopy are used to characterize the morphology of the weld.

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The thermo-oxidative degradation of the polybenzimidazole material, poly[(2,2'-m-phenylene)-5,5'- bibenzimidazole] (PBI), and of a blend of PBI with the polyetherimide, poly[2,2'-bis(3,4-dicarboxyphenoxy) phenylpropane-2-phenylene bisimide] (Ultem 1000), was investigated by Fourier transform infra-red (FTi.r.) spectroscopy. An experimental protocol and the necessary instrumentation were developed for real-time monitoring of the molecular changes occurring during the process. The spectroscopic data provided information about the mechanism and the kinetics of the thermo-oxidative degradation in its early stages. The FTi.r. spectra of the PBI/Ultem 1000 blend were analysed by subtraction spectroscopy, and the application of this technique allowed us to selectively follow the fate of the two components in the blend. No chemical interaction between PBI and Ultem 1000 was detectable by FTi.r. spectroscopy during the degradation process.

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Linear and three-arm star styrene-b-isobutylene-b-styrene block copolymers were synthesized by living cationic polymerization using ring-substituted di- or tricumyl chloride, respectively, as initiator, TIC14 as coinitiator, pyridine as an electron donor and 2,6-di-tert-butylpyridine as a proton trap in a 60/40 (v/v) methylcyclohexane/methyl chloride solvent mixture at -80°C. The polymers had equivalent compositions and segmental molecular weights allowing the effect of molecular geometry on sample morphology and physical properties to be determined. The samples exhibited a dual-phase morphology consisting of cylindrical polystyrene domains dispersed within a matrix of polyisobutylene; polymer geometry was found to have a significant effect on the tensile properties, with the three-arm star sample displaying a tensile strength twice that of the linear sample. In addition, the three-arm star block copolymer was found to have a higher rubbery plateau modulus than the linear block copolymer. Due to their perfectly saturated mid-block, polyisobutylene-based block copolymers were found to be much more thermally stable than the closely related styrene-b-(ethylene-co-l-butene)-b-styrene block copolymers (hydrogenated polybutadiene centre block).

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Differential scanning calorimetry has been used to investigate the crystallization and melting behaviour after different thermal treatments, both in the nematic and in the isotropic state, of a poly(ether ester) of low isotropization temperature obtained by reacting 4,4'-dichloroformyl-~t,~o-diphenoxydodecane and 2-methyl-hydroquinone. Isothermal crystallizations have been studied in terms of variation of the successive melting profiles as a function of various parameters; the appearance of multiple endotherms has been attributed to crystal reorganization processes. In non-isothermal experiments from the nematic or isotropic state, crystallization generally occurs partially on cooling and partially on heating, the overall enthalpy being almost constant; the effect of various parameters has been investigated and interpreted in terms of a slow rate of ordering and disordering of the nematic phase, which leads to non-equilibrium effects. The influence of the molecular weight and of the chain rigidity is briefly discussed

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The determination of the surface free energy of the chain-folding faces of crystals of ethylene-butene random copolymer is performed by fitting the most probable value of the crystal thickness distribution with the average crystal thickness assessed from small-angle X-ray scattering. The surface free energy is the adjustable parameter in the equation of the crystal thickness distribution derived from the Thomson-Gibbs relation for the melting of lamellar crystals of finite thickness. On the one hand, the steady increase of the surface free energy of bulk-crystallized copolymers with increasing co-unit concentration is relevant to a growing disorder in the amorphous overlayer of the lamellar crystals. On the other hand, the decrease of the surface free energy with increasing dilution for a given copolymer crystallized from decalin solutions is an indication of an improved regular chain folding. Both conclusions support previous studies dealing with the mechanical behaviour ofethylene-butene copolymers in relation to co-unit concentration and crystallization conditions.

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Deposition of polypyrrole tosylate, synthesized potentiostatically with values of 0.5-0.8 V (relative to a standard calomel electrode) from an aqueous solution, on a solid non-conducting surface in a specially designed thin-layer cell led to the observation of two-dimensional growth of the film directly adjacent to the surface, reverting to three-dimensional dendritic growth as the film thickness increases. The significance of the two forms of morphology is discussed

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