1992 рік

A micro-Raman mapping of the transition region corresponding to the non-oriented to oriented transformation zone in the neck was obtained for stretched poly(vinylidene fluoride) (PVF2). Since Raman spectroscopy is a technique sensitive to the change in the crystalline structure in PVF2 when this polymer is submitted to a stress, the distribution of the crystalline modification along the neck was obtained from the analysis of the micro-Raman mapping. The results show a gradual increase in the degree of crystalline phase transformation along ~ 200/lm in the stretching direction.

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The influence of cation type on the morphology and properties of model polyurethane ionomers is investigated in ionomers with different backbone types, pendant anion types and ionic group concentrations. A correlation between the degree of ordering in the local environment of the neutralizing cation and the tensile properties of the ionomers is observed. The geometrical packing constraints of the pendant anion are also seen to be a critical factor in determining the physical properties ofionomers. Differential scanning calorimetry results indicate no significant differences in the extent of phase separation of ionomers neutralized with different cations; however, anion type is shown to have a large influence on the degree of phase separation. Small-angle X-ray scattering analysis of the morphology of the ionomers reveals a correlation between the number of ionic groups per aggregate and the low-temperature storage modulus measured by dynamic mechanical analysis. The importance of the electronic structure and geometrical packing constraints of the ionic groups is emphasized

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The structural parameters of butadiene styrene diblock copolymer films prepared by deposition from toluene have been studied with the aid of small-angle neutron scattering (SANS) in the temperature range from -190 up to +210°C. The experimental scattering curves were simulated within the limits of the line-gradient model including the Debye-Waller factor, the static character of which was determined from low-temperature measurements. The structural parameters determined by SANS experiments have been compared with the parameters calculated with the help of the formulae obtained by Skoulios, Helfand and Meier. It was also observed that the system could retain information about the conditions of the superstructure formation process.

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The reactivity in the excited state of new radical photoinitiators, S-phenyl thiobenzoates, was investigated. Laser flash photolysis experiments on various substituted compounds allowed both thiyl and benzoyl radicals to be observed. These two radicals arose from the or-cleavage of the C-S bond in the first excited triplet state. The ability to initiate radical polymerization was followed by dilatometry. From the results, it is found that the S-phenyl thiobenzoate photoinitiators can be even more reactive than benzoin ethers because of their better u.v. light absorption.

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The local environment of the neutralizing cation was examined by extended X-ray absorption fine structure spectroscopy in a series of model polyurethane ionomers. Polyol type, polyol molecular weight and pendant anion type had small effects on cation local environment. Sample preparation conditions had a noticeable effect in one case. The type of cation was the dominant factor in determining local ordering. The degree of local order decreased with cation type in the order Ni 2+ > Sr 2+ > Cd 2+, in agreement with the trend of decreasing tensile properties with cation type. Hydration of Ni 2+-neutralized ionomers induced no change in the Ni 2 + local environment for a sulphonated ionomer, but hydration caused a rapid change in the local structure of the analogous carboxylated ionomer. The changes were in accord with water molecules coordinating to the Ni z+ cation.

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Morphology, fractionation and differential scanning calorimetry (d.s.c.) studies point to very-low-density polyethylene (VLDPE) being a heterogeneous blend of molecules with widely different comonomer contents. The morphology of VLDPE shows distinct regions of highly different crystallinity. This highly crystalline dispersed phase occurs in smooth, spherical compact semicrystalline domains, which are believed to be due to demixing in the melt. The mixing and demixing of a heterogeneous ethylene-octene copolymer as a function of time and temperature and the influence of crystallization on this behaviour is studied with d.s.c, and transmission electron microscopy. The results show clearly that mixing occurs at higher temperatures, that demixing occurs in the melt and that under certain conditions this demixing is binodal in character

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The effect of drawing on the oxygen permeability of poly(ether ether ketone) films has been examined. Sample characterization by density and refractive index measurements indicates that the two-fold reduction observed in passing from the amorphous isotropic to the highly drawn state is only partly explained by crystallinity increases and that molecular orientation shown by birefringence is also important.

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Dielectric and infra-red experimental evidence on methacrylate polymers is reviewed. These results are discussed in terms of a model proposed for dielectric relaxation of polar polymer in a matrix of arbitrary compliance. As the side-chain length increases, the symmetry of the orienting segment decreases, causing the strain energy to offset any reduction in the free energy due to interactions of the dipoles,/3, with the applied electric field, E.

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The registration of the signal of small angle neutron scattering from a single deuterated chain in a superstructure formed by block copolymers is difficult due to Bragg diffraction. A method is proposed to avoid this diffraction by turning the interdomain neutron contrast to zero. This is attained by means of synthesis of each block of the polystyrene-polybutadiene-polystyrene block copolymer as a statistical copolymer of H and D monomers. The radius of gyration of the deuterated polybutadiene block was measured by neutron scattering.

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Vinyl ester resins with varied acid values (11, 22, 32, 38 and 48mg KOHg-1 solid) were prepared by reacting an epoxy novolac resin with methacrylic acid. The curing and decomposition behaviour of these resins containing styrene as reactive diluent (40%w/w) and benzoyl peroxide (2phr) as initiator were studied by d.s.c, and t.g.a. The activation energy and frequency factor for the curing reactions calculated by the Ozawa method were found to increase from 17 to 24 kcal mol-1 and 1.2 x 101 o to 6.6 x l0 t 3 min-1, respectively, with increase in the acid value of the samples. An isothermal temperature for the curing of all the resins was selected from the d.s.c, scans and at that temperature the cure time was found to increase with the acid value of the resins. The cured product with the lowest acid value was found to be the most thermally stable and a lifetime of 16.58 years at 400°C was estimated. The activation energy and frequency factor for the decomposition reactions, calculated by the Coats and Redfern method, decreased from 24 to 17.8 kcal mol-1 and 1.05 x 10 6 to 1.5 x 104min - 1, respectively, with increase in the acid value from 11 to 48 mg KOH g- t solid.

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