1993 рік

The adhesion properties of aromatic polyimide films on SiO 2 and on various polyimides without any adhesion promoter were studied. Flexibility of the polyimide chains was found to be necessary for good adhesion. Polyimides with a flexible structure gave higher adhesion than those with a rigid structure for both substrate types. On SiO2, delamination occurred within 100h on exposure to steam at 120°C. On polyimides, the adhesion depended on both the substrate and the coating, and the peel strength increased in the following order of coating/substrate combinations: rigid/rigid < flexible/rigid < rigid/flexible < flexible/ flexible. For the case of a rigid polyimide substrate, the adhesive property was greatly improved when coatings were spun on partially imidized substrate. This suggests that the dominant factors affecting adhesion are the degree of freedom of the molecular chain, which will affect the interaction between polyimide and SiO2, and the diffusibility of the molecular chain at the polyimide/polyimide interface. The existence of a diffusion layer was observed at the polyimide/polyimide interface with energy-dispersive X-ray analysis/transmission electron microscopy.

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The phase behaviour of blends of poly(1-vinyl-2-pyrrolidone) and poly(vinyl formal) was studied by means of differential thermal analysis and differential mechanical thermal analysis. Both techniques showed that the blend studied exhibits a single glass transition, which is intermediate between the glass transitions associated with each constituent polymer and depends on polymer concentration. Discussion of this phase behaviour in terms of various common equations is also carried out. The blend preparation method as well as the blend thermal history are found to exert a relevant influence on the phase behaviour associated with the polymer alloy studied here. This behaviour is explained as the consequence of hydrogen-bonding interactions between both polymers as demonstrated by infra-red spectroscopy. An additional study on the mechanism of complex formation associated with poly(1-vinyl-2-pyrrolidone) and poly(vinyl butyral) is also carried out.

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Using 35C1 elastic recoil detection (ERD) analysis, oxygen enrichment was found on the surfaces of polystyrene and a random copolymer of styrene and acrylonitrile containing 38.7 wt% acrylonitrile. The samples were prepared in a hot press at 200°C between two silicon wafers in an air environment. The oxygen-rich layer on top of the samples was less than 20 nm thick. Heavy ion ERD seems to be a promising method to study the chemical composition of polymer surfaces and concentration profiles up to a depth of several hundred nanometres

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Thermal polymerization of bis(pyridine)bis(trichlorophenoxo)copper(II) was achieved in the solid state for the first time. The time and temperature effect on polymer molecular weight, percentage yield and the structure of polymer was first studied, at constant temperature and then for constant decomposition time. Polymers were characterized by i.r., 1H n.m.r, and ~3C n.m.r. The molecular weights of the polymers were obtained by viscometric measurements at 30°C in toluene and glass transition temperatures were obtained by d.s.c.

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The concentration and temperature dependences on micelle formation by a polystyrene-blockpoly( ethylene/propylene) copolymer in several ketones (methyl ethyl ketone, methyl propyl ketone, diethyl ketone, methyl isobutyl ketone, dipropyl ketone, 5-methyl-2-hexanone and 5-methyl-3-heptanone) are studied by laser light scattering and viscometry. No micelles were detected in solutions of 5-methyl-3- heptanone. The standard Gibbs energy, AG °, the standard enthalpy, AH °, and the standard entropy, AS °, of micellization were estimated from the dependence of the critical micelle temperature on concentration. The values of AG °, AH ° and AS ° were negative for all ketones studied. AG ° and AH ° depend on the polar character of the ketone. The weight average molar mass, second virial coefficient and apparent radius of gyration have been calculated from the standard Zimm plots obtained. Huggins and Kraemer equations have been employed to determine the limiting viscosity number of the micelles. The micelles formed in ketone solutions show larger association numbers and densities than those formed in n-alkane solutions.

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The optical properties in the visible wavelength range (400-800nm) of solution-cast, ultra-drawn, ultra-high-molecular-weight polyethylene (UHMW-PE,)~,>106gmol 1) films were investigated. UHMW-PE films, drawn 30 times at 125°C, possess a rather low transmittance (40-60%) in the visible wavelength range. However, highly transparent films with a transmittance exceeding 90% are obtained by applying a surface coating to the films. Dichroism in the visible wavelength range can be generated in drawn UHMW-PE films by incorporating dichroic dyes. Certain dichroic dyes were found to orient during solid-state drawing. Dichroic UHMW-PE films with a dichroic ratio of 30 and an order parameter of 0.91 were produced

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Three novel diamines containing pendent ethynyl, hexynyl and phenylethynyl groups were synthesized and used to prepare polymers and copolymers. When heated to 250-350°C, the ethynyl groups react to form crosslinks. After curing, the homopolymers were brittle owing to the high crosslink density. Copolymers prepared using 10mol% ethynyl-containing diamine and 90mo1% of diamines with no ethynyl groups were relatively tough, forming creasible films. After a thermal cure, the copolymers became insoluble and exhibited high Tg values and good thin film properties.

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Inverse gas chromatography has been used to investigate the thermodynamic compatibility of blends of poly(vinyl chloride) (PVC) and nitrile rubber (NBR) as a function of blend composition and acrylonitrile (AN) content of NBR. The values of the polymer-polymer thermodynamic interaction parameters (Z~3 and B23 ) and the solubility parameter (6) of the polymers and their blends were determined with the help of the measured retention data for various polar and non-polar probes in the pure and mixed stationary phases of these polymers. Out of all the probes studied only dioxane and cyclohexanone have similar values to those of the blends. The B23 values for the PVC/NBR blends were ~-0.i and -1.1 cal m1-1 depending on the AN content of NBR. Thus, the two polymers are fairly compatible and show increased compatibility with increase in AN content of NBR.

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The interfacial tensions between BPA polycarbonate (PC) and a series of styrene-acrylonitrile (SAN) blends having S/AN ratios varying between 100/0 and 60/40 (wt%) have been determined by measuring capillary thread breakup rates at 200°C. A distinct minimum in the interfacial tension is observed close to the SAN composition reported to show maximum miscibility with PC. For the case of PC/PS, the measured values are compared with those calculated from published studies on PS/poly methyl methacrylate (PMMA) and PC/PMMA.

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Segmented block copolymers based on dimerized fatty acids and poly(butylene terephthalate) (PBT) have been synthesized in the melt. Branched C36, C44 and C70 dimerized fatty acids with a low degree of unsaturation were used. The fraction of PBT was varied from 50 to 100 wt%. The resulting polymers were analysed with d.s.c, and d.m.a. The glass transition temperature (T~) increased with increasing weight fraction of PBT. T~ decreased with increasing molecular mass of the dimerized fatty acid. The melting temperature increased with increasing weight fraction of PBT and increasing molecular mass of the dimerized fatty acid. The range of service temperatures of the thermoplastic elastomers can therefore be enlarged by using dimerized fatty acid with a high molecular mass. With increasing molecular mass of the dimerized fatty acid the storage modulus and the melting and crystallization enthalpy did not change significantly. The storage modulus can be described as a function of the volume fraction of crystalline PBT, but is not a function of the type of dimerized fatty acid.

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