1992 рік

Semicrystalline segmented polyurethanes based on hydrogenated polybutadiene (H-PBD) soft segments and butanediol (BDO) or di-fl-hydroxyethyl hydroquinone (HQEE) as chain extenders were synthesized under different homogeneous or heterogeneous conditions, in solution or in bulk. Segmented semicrystalline H-PBD polyurethanes exhibit two glass transitions: a soft-phase transition Tg(S) and a hard-phase transition Tg(H). Thermal treatments show rearrangements in the two-phase materials. The dielectric relaxations, ct s and ctH, confirm the thermal behaviour and also the presence of a mixed interfacial region (~h). Increasing the hard-segment content increases this mixed-phase relaxation. This effect is also observed in the polyurethanes prepared in bulk instead of in solution, because of the decrease in the segregation ratio of the soft segments. Bulk samples also contain short isolated or amorphous hard segments as shown by size exclusion chromatography results and the conduction process appearing in the dielectric measurements. Such different routes of preparation induce various characteristics and tensile properties of the corresponding polyurethanes attributed mainly to premature phase separation occurring during the polymerization and the competition between the phase separation rate and the polymerization rate.

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The morphology of injection-moulded blends of polycarbonate (PC) and acrylonitrile-butadiene-styrene (ABS) has been examined across the entire composition range. Brittle fracture surfaces were etched to remove selectively the PC phase and viewed in the scanning electron microscope. Morphological features observed through the thickness of injection-moulded plaques were the basis for the identification of three composition ranges. In PC-rich blends, the ABS phase formed a bead-and-string structure oriented in the injection direction near the edge, while in the centre the ABS was dispersed as rubber domains and spherical particles of free styrene-acrylonitrile (SAN). A transition occurred between PC/ABS 70/30 and 60/40 wt% compositions from the bead-and-string structure with some interconnections to a coalesced, stratified morphology near the edge; while in the centre, the morphology changed from a dispersion of rubber particles and free SAN particles to thick coalesced ABS domains that created regions where ABS was co-continuous with PC. The ABS-rich blends had a conventional blend morphology with PC domains dispersed in ABS. Qualitatively, the solid-state morphology could be explained in terms of the melt morphology created by the melt flow pattern during mould filling, and subsequent relaxation during cooling prior to solidification

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The absorption spectra of emeraldine base and the fully reduced leucoemeraldine in N-methylpyrrolidinone (NMP) indicate that the former is stable in this solvent but the latter undergoes oxidation of the amine units to imine units in the presence of dissolved oxygen. The presence of imine units is confirmed by X-ray photoelectron spectroscopy and infra-red absorption spectroscopy. Under light irradiation, this oxidation process is accelerated. Both this polymer and emeraldine base undergo further degradation of the polymer chain. Comparison of the spectra of leucoemeraldine and emeraldine base solutions with aqueous HCIO 4 added indicates that protonation can occur at the amine units of the former, although this process is not as effective as protonation of the imine units of emeraldine base. The polymers gradually undergo deprotonation resulting in quinoid-imine structures in both cases when oxygen is present, and the deprotonation process is also accelerated by light. On the other hand, the addition of Cu(CIO4) 2. 6H20 to the leucoemeraldine and emeraldine base solutions results in the polymers approaching the fully oxidized state which is much more stable under light irradiation than the pristine polymer solutions. The similarities and differences between the results obtained in solution and in solid-state are also discussed.

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A thermotropic liquid crystalline copolyester formed by polycondensation of 8-(3-hydroxyphenyl) octanoic acid (3-HPOA) and p-hydroxybenzoic acid has been synthesized and characterized. 3-HPOA having both a flexible segment and a rigid kink in its structure has been synthesized by phase transfer catalysed oxidation of cardanol. The copolyester was anisotropic under crossed polarized light between 200°C and 409°C. D.s.c. showed two mesophase transitions with maxima at 256°C and 342°C, respectively

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Films of ultrahigh-molecular-weight (3 ? 10 6) polyethylene were produced by gelation/crystallization at various temperatures from dilute decalin solutions according to the method of Smith and Lemstra. The temperatures chosen were 20, 30, 50 and 70°C. With increasing temperature, the long period and crystallinity of the resultant gel film increased. By contrast, when the films were stretched up to 300 times, the increases in Young's modulus, crystallinity and molecular orientation become more significant as the temperature ofgelation/crystallization become lower. This interesting phenomenon is thought to be due to the dependence of the number of entanglement meshes on the temperatures of gelation/crystallization and evaporation of solvent from the gel to form a film

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Cross polarization/magic angle spinning (CP/MAS) 13C n.m.r, measurements have been performed at room temperature for poly (vinyl alcohol) (PVA) films with different tacticities to obtain information about the structure and hydrogen bonding in the crystalline and non-crystalline regions. 13 C spin-lattice relaxation analyses have revealed that three components exist for each sample, with different spin-lattice relaxation times Tic, which are assignable to the crystalline, less disordered non-crystalline and amorphous components. Using such differences in Tic, we separately recorded the spectra of the crystalline and non-crystalline components, and then analysed the triplets of the CH resonance lines appearing in both spectra in terms of three Gaussians which should be ascribed to CH carbons associated with two, one and no intramolecular hydrogen bond(s) in the ram, mr and rr sequences. As a result, it has been found that the relative intensities of the triplets are not in accord with the contents of the triad sequences, suggesting the formation of intramolecular and intermolecular hydrogen bonds in the meso sequences at almost equal probability. The effects of water on hydrogen bonding have also been examined for the almost atactic PVA sample.

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Two models have been proposed to explain the two melting endotherms commonly observed in polyethers: (1) the crystals with the lower melting temperature may transform into a higher melting form during heating; (2) the two melting peaks come from separate populations of crystals. Our TEM studies of thin films of PEEK have shown two crystal populations, with widely differing lamellar thicknesses, which can occur in quite separate areas of the samples. These results strongly support the second model.

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The synthesis and living cationic polymerization of 5-[(4-cyano-4'-biphenyl)oxy] pentyl vinyl ether (6-5) and 7-[ (4-cyano-4'-biphenyl)oxy] heptyl vinyl ether (6-7) are presented. The influence of molecular weight on the mesomorphic behaviour of poly(6-5) and poly(6-7) is discussed and compared to that of 5-[- (4-cyano-4'-biphenyl)oxy] pentyl ethyl ether (8-5) and 7-[- (4-cyano-4'-biphenyl)oxy] heptyl ethyl ether (8-7) which are models of the monomeric structural units of poly(6-5) and poly(6-7). Both (8-5) and (8-7) exhibit a monotropic nematic mesophase. Poly (6-5) with degrees of polymerization equal to and lower than six exhibit an enantiotropic nematic mesophase. Poly(6-5)s with higher degrees of polymerization display both smectic A and nematic enantiotropic mesophases. Poly (6-7) exhibits an enantiotropic smectic A mesophase over the entire range of molecular weights.

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Ozonization seems to be an interesting way to create reactive sites when the aim is to optimize radical grafting of vinyl monomers on polypropylene. In order to extensively follow the grafting parameters we used the spin-probe technique of electron spin resonance as well as the spin-trapping technique in conjunction with the diffraction and morphological techniques of transmission electron microscopy. The data indicate that ozonization modifies the diffusion mechanism of liquid monomers in the polypropylene matrix and suggest that grafting takes place in the amorphous phase. We also showed that a core-shell morphological structure can be observed on ozonized polypropylene (granules and fibres). Further, information on peroxide location was obtained.

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It has been shown that benzyl alcohol is transformed rapidly and almost quantitatively into poly(phenylenemethylene) by adding it to anhydrous hydrogen fluoride at 16°C; the product is the so-called 'soluble poly(phenylenemethylene)' with a degree of polymerization of ~ 20. p-Methylbenzyl alcohol has also been oligomerized by a similar procedure. The potential for adaption to industrial-scale use is highlighted.

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