1994 рік

Two symmetrical imide diacids were prepared from trimellitic anhydride and two cqco-diamines containing ether linkages, namely 1,8-diamino-3,6-dioxaoctane and 1,12-diamino-4,9-dioxadodecane. Polycondensations in the melt of the imide diacids and diacetyl bisphenols yielded the corresponding series of poly(ester imide)s (PEIs), characterized by an alternating sequence of stiff, aromatic imide units and ether-containing aliphatic spacers. The presence of-O- linkages within the flexible spacers greatly affected the thermal transitions and the thermotropic behaviour of the PEIs. Comparison with homologous PEIs without ether linkages revealed lower glass transition temperatures and a weaker tendency to form liquid crystal mesophases. Only the PEIs from 4,4'-dihydroxybiphenyl showed a regular thermotropic behaviour, as could be proved by optical microscopy with crossed polarizers, by d.s.c, and by synchrotron radiation measurements at variable temperature. These PEIs form layer structures in the solid and liquid state. The textures suggest the formation of a smectic-A phase.

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Four binary blends were studied, each containing the same lightly branched polyethylene with one of a series of linear polyethylenes (LPEs) of varying molecular weight. Liquid-liquid phase separation was observed in all blend systems but one. The liquid-liquid phase separated regions were in the form of closed loops, asymmetrically placed at low linear polyethylene content. The liquid-liquid phase separated regions were found to decrease in size as the molecular weight of the LPE decreased, very slowly where the molecular weight of the LPE was high but more rapidly by the time that the molecular weight of the LPE fell to 2 ? 104. In the fourth system, where the molecular weight of the LPE was 2500, no liquid-liquid phase separation was seen. This system fills a logical position in the sequence: the liquid-liquid phase separated region has reduced to zero in size at this very low LPE molecular weight. This communication contains additional data on systems previously studied in part -- the liquid-liquid phase separated regions had been recorded only for temperatures just above the melting point of the LPE. Now, as a result of improved experimental techniques, the full liqui~liquid phase separated loops, including upper critical temperatures, are reported.

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Rheological properties, determined by torsion experiments, of three main-chain thermotropics are investigated. Stable, time-independent measurements are obtained in two of these polymers, and the corresponding dynamic viscoelastic and first normal difference results are analysed. In the nematic state both storage and loss moduli scale as G', G"oc o91/2, and no shear modulus associated with an entanglement network is detected. Recoverable compliances jo, which are determined from steady-state N~ values, are several orders of magnitude higher than those of isotropic polymers. For one of the polymers, the characteristic molecular weight between entanglements, Me, is determined from Newtonian viscosities of isotropic solutions. Although the molecular weight of our sample is above M~, viscoelastic measurements at temperatures corresponding to the nematic state show no vestige of the entanglement network.

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We have used neutron reflectivity and helium (3) nuclear reaction analysis to measure adsorbed amounts and concentration profiles of carboxy-terminated polystyrene chains in the melt, which are physically end-adsorbed onto the native oxide layer on silicon substrates. The excess of adsorbed chains at the substrate increases with annealing time, but more slowly than predicted by a model. We have measured the adsorption isotherm for this system. By comparison with numerical solutions of self-consistent field equations we deduce a sticking energy of 8.6 kT per molecule.

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(Received 2 December 1993, revised 30 June 1994) The tyt.q' conformation of poly(vinylidene fluoride) (PVDF) is ~ 0.5-0.7 kcal mol - J monomer- t more stable than the all-truns conformation as calculated by molecular mechanics. For vinylidene fluoride-trifluoroethylene copolymer compositions < ~90mo1% vinylidene fluoride, the all-trans conformation is more stable. For PVDF, crystal packing calculations support the distorted tgt.q' conformation predicted by X-ray crystallography.

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The system poly(ether ether ketone) (PEEK)/PET-PHB 60 has been studied by differential scanning calorimetry and scanning electron microscopy (SEM). The thermal analysis data, especially the glass transition temperatures, indicate that the blends are compatible. The SEM analysis seems to confirm this, showing a mostly homogeneous structure. When the two phases are still evident, a good adhesion is shown; this is of interest in terms of the mechanical properties, results for which are not yet available.

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The cationic photopolymerization of cyclohexene oxide and 4-vinylcyclohexene dioxide was achieved by using charge-transfer (CT) complexes of pyridinium salts and aromatic electron donors (hexamethylbenzene and 1,2,4-trimethoxybenzene) as initiators. Irradiation of the CT complexes with light of relatively long wavelength produces radical cations of the aromatic electron donors capable of initiating cationic polymerization. N-Vinylcarbazole and n-butyl vinyl ether are spontaneously polymerized in CH2C12 solution in the dark at room temperature upon addition of the CT complexes mentioned above. The molar extinction coefficients ~ct and equilibrium constants Kct of the CT complexes have been determined.

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Structurally organized solutions containing monomers in an ethylene glycol (EG) medium were formed and polymerized to produce polymeric solids with various morphologies, and also unique thermal and mechanical properties. Previous research had demonstrated the formation of microemulsions in an aqueous medium containing methyl methacrylate (MMA) and acrylic acid (AA). However, the non-aqueous mixtures of MMA and AA with EG did not yield conventional microemulsions. Molecularly dispersed solutions were formed in the bulk of the phase diagram, while compositions closer to the demixing line exhibited critical behaviour. This paper presents the first account of the use of mixtures exhibiting critical behaviour to produce microstructured polymers. The non-aqueous mixtures did not form any well defined microstructures on polymerization for compositions away from the two-phase boundary. Compositions exhibiting critical behaviour yielded open cell structures and also beaded polymers at high EG contents. This suggests that the microstructure in these mixtures is preserved in the final polymer to a considerable extent. The virgin polymers containing EG had very low glass transition temperatures due to the plasticizing nature of EC. The plasticizing nature of EG was also evidenced in the tensile properties of the virgin polymers

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Biaxially stretched polypropylene (PP) foils treated with oxygen plasma at low pressure were analysed by core level and valence band region X-ray photoelectron spectroscopy (XPS), atomic force microscopy and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. Applying short treatment times the XPS O~C atomic ratios are ~<0.1. Valence band electron spectroscopy for chemical analysis (ESCA) and NEXAFS spectroscopy reveal that a certain number of C-O and a smaller amount of C--O functionalities together with C=C bonds exist at a short-time treated PP surface. These species were not observed or resoh'ed by a standard core level XPS analysis of the same surface. The surface is smoothed by the plasma treatment and the C-O and C~O bonds are slightly non-statistically oriented (parallel to the surface plane). Considering the results obtained after prolonged plasma treatment, NEXAFS spectroscopy provides a direct indication for the formation of conjugated carbon double bonds in the surface region of the PP samples. (Keyw'ords: polypropylene; plasma treatment; spectroscopy)

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Crosslinked copolymers of methyl methacrylate with N-vinyl-2-pyrrolidone of various compositions were prepared to high conversion by ?-irradiation and swollen in water to yield equilibrium water contents of 15-76 wt%. Differential scanning calorimetry was used to probe the states of water in the hydrogels prior to equilibrium swelling. Diffusion coefficients of water decreased about 100-fold as the effective crosslinking density of the polymers increased by the same factor. The relative uptake of the non-freezing water was found to be more rapid than that of the total freezing water.

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