1992 рік

We have found that swelling the surface of ultra high molecular weight polyethylene (UHMWPE) with an organic solvent and then subsequently cooling with the solvent present can significantly modify surface properties. In particular, metal/polymer adhesion can be enhanced and, if graphite is added to the solvent, surface conductivity can be enhanced. The enhanced adhesion properties may relate to an increased ductility of the preswollen polymer at elevated temperatures. The modified conductivity can be attributed to graphite particles trapped at the surface of the material. In order to qualitatively explain some of our results, rheological and optical observations on UHMWPE melts are also presented.

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Nascent poly(fl-hydroxybutyrate) (PHB) granules are found in most bacterial strains and can be isolated as a milky suspension. Their structure was examined by transmission and scanning electron microscopy and has been shown to be made of two distinct components: a solid shell composed of overlapping lamellar crystals and a soft non-crystalline core. It was possible to obtain a ductile deformation of the core in liquid nitrogen even though the glass transition of isotactic PHB approaches 0°C. Finally, glycerol triacetate, a minor component of the granule, was found to be a good solvent for PHB from which metastable solutions can be obtained. Self-seeding of these solutions led to the formation of lamellar crystals comparable to the structure of the shells

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A new tetrachloroferrate-doped (FeC14) salt of emeraldine (polyaniline) has been obtained in a non-aqueous medium. From elemental analysis and M6ssbauer studies, the salt has been identified to contain iron exclusively in the + 3 oxidation state. Data on temperature-dependent d.c. conductivity and dielectric constant measurements on the doped polyaniline salt in the X-band of the microwave region are also discussed

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Soaking of nylon 6 and 66 films in saline solutions modifies their deformation response to an applied tensile stress. Unsalted films do not show conventional crazes. Instead they are seen to deform by a mixture of shear and fibrillated shear, the latter involving chain disentanglement. Dried salt-soaked films are, however, dominated by scission crazing for all temperatures below the glass transition temperature. Salt treatment modifies intermolecular bonding, strengthening it in the process, and stiffens the polymer chains. Such modifications act to suppress shear and chain disentanglement. Calcium and zinc chlorides both reduce the temperature dependence of the strain for deformation onset and embrittle films, with nylon 6 much more affected than nylon 66. Sodium chloride acts only as a weak crazing agent for both nylon types

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Anionic polymerizations of methyl methacrylate, n-butyl methacrylate and tert-butyl methacrylate with 1,1-diphenylhexyllithium in THF at 195 K were performed. By characterizing the resultant polymers, the controllable limits of molecular weight and molecular weight distribution were examined. Tert-butyl methacrylate gave a polymer with a high molecular weight (1.8 x 105) and narrow molecular weight distribution (Mw/M . = 1.0 7). A well-defined block copolymer of'tert-butyl methacrylate with styrene or c~-methylstyrene was obtained by intermediate addition of l,l-diphenylethylene.

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An electroactive elastomeric material was prepared by the electrochemical graft copolymerization of aniline with nitrile rubber. The synthesis has been carried out potentiostatically, potentiodynamically or galvanostatically in a non-aqueous medium using a nitrile-rubber-coated working electrode. Infra-red spectra of the products resemble a superposition of nitrile rubber and polyaniline spectra. However, thermogravimetry, differential scanning calorimetry and solubility experiments indicate that the polyaniline chains grow as grafted branches of the nitrile rubber chains. Scanning electron microscopy indicates no phase segregation in accordance with this assumption. Cyclic voltammetry experiments indicate that the new material has the same electroactivity as pure polyaniline

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Solution state n.m.r, techniques have been used to study 10% w/v aqueous solutions of methylcellulose, hydroxypropylcellulose and hydroxypropylmethylcellulose. 13 C n.m.r, spectra taken at temperatures from ambient to 70°C show loss of peak intensities of both backbone and substituent signals due to liquid/solid phase separation processes at high temperatures. The substituents on methylcellulose become immobile and those on hydroxypropylcellulose retain mobility. This information is interpreted on the basis of the different structures of the solid phases and the thermodynamics of the phase separation process.

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Transparent, adhesive and viscoelastic polymer electrolytes were synthesized from poly(propylene glycol) (PPG) (molecular weight 2000), poly (methyl methacrylate) (PMMA) and LiCF3SO 3 for smart-window application. The synthesis was carried out by the matrix polymerization method. Methyl methacrylate was polymerized in PPG doped with LiCF3SO3 using azobisisobutyronitrile as the initiator. Interestingly, the presence of LiCF3SO3 makes the two otherwise incompatible polymers compatible. Various combinations of the salt and PMMA were tried to make it applicable for smart windows. The PMMA incorporated (up to 8%) by this method appears to form a protective coating for the PPG-salt complex, making it hydrophobic, and also increases the adhesiveness of the polymer electrolyte. The ionic conductivities of these polyelectrolytes were measured as a function of temperature. The plot of conductivity versus temperature was found to fit to the Vogel-Tammann-Fulcher equation over the temperature range -20 to 110°C. The glass transition temperature was determined by differential scanning calorimetry. At high O:M ratio (ratio of ether oxygens to alkali-metal cation), PMMA does increase the Tg of the system, as can be expected. However, at low O:M ratio, PMMA does not seem to have any influence on the Tg of the system. The PMMA was isolated from the reaction mixture and characterized by 1H nuclear magnetic resonance and gel permeation chromatography analysis.

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Crystalline poly(3-phenyl-4-hydroxybenzoic acid) was prepared by polycondensation of 4-acetoxy-3- phenylbenzoic acid in solution at 320°C. Differential scanning calorimetry (d.s.c.) and wide angle X-ray scattering (WAXS) measurements indicate that this homopolyester forms a nematic melt between 345°C and 465°C. Five copolyesters of 4-hydroxybenzoic acid (HBA) and 4-hydroxy-3-phenylbenzoic acid ( 3-PhHBA ) with varying molar composition were prepared by polycondensation in solution. One additional copolyester was prepared by polycondensation in bulk. 1H n.m.r, spectroscopy revealed a significantly lower reactivity of the phenyl-substituted acetoxybenzoic acid. The influence of the molar composition on crystallinity, phase transitions and stability of the nematic mesophase was studied by d.s.c, and WAXS measurements and by optical microscopy. Heat distortion temperatures were determined by the penetration method. It was found that the copolyesters prepared in bulk and in solution possess quite different properties. Only the copolyester prepared in bulk forms a nematic melt above its melting point at 205 +_ 3°C.

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Glass transition temperatures (Tgs), heats of fusion and crystallization and specific heats in the solid phase, for a series of statistical copolyamides (nylon-8/nylon-12), prepared by activated anionic polymerization of octane-/laurolactam (OL/LL), were determined and the results were correlated with the molar composition of the copolyamides and discussed. Minima for Tg and the heat of fusion for the initial melting and maxima for Tg/initial melting point (Tin) and changes in specific heat values were indicated for copolyamides with 50/50-60/40 molar compositions.

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