1992 рік

This paper is concerned with a novel ternary blend composed of poly(ether imide) (PEI), poly(ether ether ketone) (PEEK) and a liquid crystalline polymer (LCP; HX4000, Du Pont). Different compositions were prepared by extrusion and injection moulding. Dynamic mechanical thermal analysis and the observation of the fracture surfaces, before and after annealing, allowed determination of the cold crystallization temperatures and miscibility behaviour of these systems. PEEK/PEI blends are known from previous studies to be miscible at all compositions. In this case it was observed that the PEEK/HX4000 blend was miscible up to 50 wt% HX4000 but partially miscible above this value. The PEI/HX4000 blends were found to be partially miscible in the whole concentration range. As a result, some ternary blend compositions exhibited only one phase, while others exhibited two phases. The measurement of the tensile properties showed that ternary blends with high modulus can be obtained at high LCP loadings, while compositions with high ultimate tensile strength can be obtained with high loadings of PEI or PEEK.

Детальніше...  

Due to the specific nature of thermally stimulated creep (TSCr) experiments, complementary data on the high temperature retardation mode in epoxy-aromatic amine networks as observed in dynamic mechanical thermal analysis have been obtained. Two series of amine-cured diglycidyl ether of bisphenol A (DGEBA) networks were investigated by TSCr to characterize their anelastic properties. By systematically varying the amount of methylene dianiline (MDA) used as crosslinking agent, the effect of an excess of epoxy on the network structure was followed. The high temperature retardation mode associated with the glass transition was found to be shifted to higher temperatures with increasing hardener content. This reveals an important restriction of molecular mobility as the resin tends to full crosslinking. It is also important to note that the peak temperature of DGEBA-MDA depends on the crosslink density for aminohydrogen to epoxy ratio r> 0.6 and on number average molecular weight for r<0.6.

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The interfacial tension Q between the coexisting phases of the systems methylcyclohexane/polystyrene and cyclohexane/polystyrene was measured by means of the spinning drop and sessile drop methods as a function of (T, - T)/T, = z, the reduced distance from the critical temperature, for different relative molar masses M of the polymer (17 500-175 000). The minimum z value that could be realized amounted to 1.7 x 10e3 and the corresponding u value to 0.0007 mN m-l. The results were evaluated according to the relations (1) lna=A-[,lnM+plnz and (2) lnAcp=B-[,lnM+filnz in which Acp is the difference in the volume fraction of the polymer in the coexisting phases, A and B are constants for a given solvent, and [,,, is, p and fi are the critical exponents. With increasing M the exponent p is found to fall from values which are close to that predicted by the mean-field theory (1.50) to those resulting from the Ising model (1.26) ; p equals 0.35 in the entire region of M (mean-field : 0.50, Ising : 0.31). In contrast to the critical exponents, A and B are not universal constants but vary from solvent to solvent, i.e. the above relations are of little use for the prediction of 0. This deficiency can, however, be overcome by substituting z from (2) into (1) and replacing M by N, the number of monomeric units. The different parameters of the resulting relation (3) In Q = D + 6 In N + (pi/?) In Acp no longer depend on the particular chemical nature of the system. It therefore constitutes a useful master curve to obtain 0 from knowledge of the composition of the coexisting phases. The evaluation of the present measurements together with unpublished material yields D = ln[O.l53(mN m-l)], 6 = (lap/b) - 4, = 0.50 (identical with the mean-field value) and p//3 = 3.85 (mean-field : 3.00, Ising -4.00).

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A solid state ~3C cross-polarization/magic angle spinning n.m.r, study was carried out to elucidate the structure of carbofuran inside starch crosslinked by urea formaldehyde. It was confirmed that carbofuran is physically entrapped in the matrix. Linewidth measurements showed the maximum degree of crosslinking occurs for a urea to starch ratio of 0.6 (w/w). The observed trends in relaxation times showed that release and swelling phenomena are partly governed by the relaxation mechanism. This conclusion is similar to that obtained from in vitro release kinetics of carbofuran from crosslinked starch matrix.

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An experimental set-up is described to determine the concentration profile of a polymer labelled with a fluorescent dye at the interface with a compatible unlabelled polymer. This method is applied to a study of interdiffusion in blends of labelled polystyrene with poly(cyclohexyl methacrylate) and compared with tracer diffusion of labelled polystyrene in the same system.

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A new isothermal equation of state for polymers in the solid and the liquid is given by P = B(T, O)/(n -- m){EV(T, 0)/V(T, P)]"+' - [V(T, O)/V(T, P)]'+' } where n = 6.14 and m = 1.16 are general constants for polymer systems. Comparison of the equation with experimental data is made for six polymers at different temperatures and pressures. The results predict that the equation of state describes the isothermal compression behaviour of polymers in the glass and the melt states, except at the transition temperature

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The lithographic evaluation of monomethyl itaconate (MMI) and methyl methacrylate copolymers as thermally crosslinkable electron beam resists is described. Their properties were investigated as a function of copolymer composition and primary molar mass in order to determine an optimum formulation for the preparation of high resolution resist patterns. Line and space test patterns with features ~0.5 pm have been prepared using copolymers containing 10 mol% MM1 with lithographic sensitivity of N 80 PC cm-* and resist contrast of N 4 cm2 PC- ’ when developed in a mixture of n-butyl acetate and n-hexyl acetate. In accordance with previously published results, the electron exposure dose required to first destroy the pre-crosslinked fraction of the resist has been found to be very much less than the electron exposure dose required for the preparation of high resolution resist patterns. The results obtained in this work are compared to a theory of gel degradation originally developed to describe the solubilization of lignin from plant tissue, whereby the breakdown of the gel can be modelled using the statistics for random network formation, except applied in reverse

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Block copolymers of aromatic polyamides have been synthesized. The polymers contain stiff, liquid crystal forming blocks and flexible blocks. A series of polymers with differing lengths of the flexible block have been prepared. The polymers have been spun into fibres from liquid crystalline solutions and the properties of as spun and heat treated (500 and 370°C) fibres have been determined. The incorporation of flexible blocks in the stiff polymer resulted in a decrease in Young's modulus and tensile strength while the elongation at break was largely unaffected. The heat treatment resulted in an increase in the Young's modulus of the fibre. The fibre containing the longest flexible block became brittle and stiff towards bending upon heat treatment. The results are discussed in terms of the influence of the block copolymer structure on the fibre morphology.

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We describe a simple light scattering set-up for measuring interdiffusion coefficients D in polymer blends by generating spinodal decomposition and subsequent dissolution after temperature jumps across the phase boundary. In blends of polystyrene and polymethylstyrene (random copolymer of 60% m-methylstyrene and 40% p-methylstyrene) D values were obtained between 10-11 and 10-15 cm 2 s-1 at temperatures up to 50 K above the upper critical solution temperature. The results are discussed in relation to tracer diffusion in the same system

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A theory of dry (containing no solvent) layers of polymer chains grafted onto the internal and external surfaces of an infinite cylinder has been developed. The geometric and thermodynamic characteristics of layers were investigated for two cases: for chains of the same length (monodisperse distribution) and for a mixture of chains of two different lengths (bidisperse distribution). It is shown that the thermodynamic advantage of mixing chains of different lengths demonstrated previously for the case of a planar layer is particularly pronounced for a concave cylindrical layer densely filling a cylindrical pore. The results obtained make it possible to investigate the thermodynamics of superstructures formed by mixtures of diblock copolymers of the AB type with different block length.

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