1994 рік

Lamellar crystal organization and spherulite formation were investigated as functions of melt polymer concentration and isothermal crystallization temperature for the model eutectic-forming system isotactic polypropylene (iPP) and hexamethylbenzene. Permanganic etching and scanning electron microscopy were used to reveal iPP crystal features. The results were interpreted in terms of the kinetics of crystallization events during thermally induced phase separation of this system. (Keywords: isotactic polypropylene; hexamethylbenzene; crystal morphology)

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Two-site model analysis was carried out for 13C n.m.r, of polypropylene polymerized by Ziegler-Natta catalyst with external alkoxysilane donors. Four effects of the external donors were found: selective poisoning of symmetric site; transformation of a symmetric to an asymmetric (but fluctuating) site; increase of whole isotacticity due to that of polymers obtained by the fluctuating site; and increase of isotacticity of the polymers obtained by the fluctuating site when the concentration of external donor is high enough.

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The electroactivity and electrochromism of the graft copolymer of poly(aniline) and nitrilic rubber were studied by cyclic voltammetry, frequency response analysis and spectroelectrochemistry in the visible range. The mechanical properties were determined by stress-strain measurements. Results indicate that the graft copolymer exhibits mechanical properties similar to a crosslinked elastomer with the electrochromic and electrochemical properties typical of oxidized poly(aniline).

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The mechanical properties of tactic poly(vinyl methyl ether)/polystyrene (PVME/PS) blends are investigated as a route to toughened polymers by using the lower critical solution temperature (LCST) behaviour as a mechanism for the production of rubbery domains. Crystallites in the tactic PVME-rich phase act as physical crosslinks. Shear bands as well as crazes are observed in these in situ composites due to interaction between a PS matrix plasticized with PVME and the PVME-rich rubbery domains.

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A quantitative study on the formation of carbonaceous char at 350, 500, 650 and 800°C in unplasticized poly(vinyl chloride), acrylonitrile-butadiene-styrene and especially in blends of the two polymers has been carried out. Incorporating iron compounds at varying levels into the polymer blends dramatically increases char formation even at 800°C. Flammability and smoke data are also presented and the relationship between char formation and levels of iron present are discussed. Crosslinking/char-forming schemes are proposed in an attempt to explain the action of iron compounds in these polymer formulations.

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Several small-molecule hosts form clathrates or inclusion compounds (ICs) with polymers. In these polymer ICs the guest polymer chains are confined to occupy narrow channels in the crystalline matrix formed by the host. The walls of the IC channels are formed entirely from the molecules of the host, and they serve to create a unique solid-state environment for the included polymer chains. Each polymer chain included in the narrow, cylindrical IC channels (ca. 5.5/~ in diameter) is highly extended and also separated from neighbouring polymer chains by the host matrix channel walls. The net result is a solid-state environment where extended, stretched (as a consequence of being squeezed) polymer chains reside in isolation from their neighbours inside the narrow channels of the crystalline matrix provided by the small-molecule host. Comparison of the behaviour of isolated, stretched polymer chains in their crystalline ICs with observations made on ordered, bulk samples of the same polymer are beginning to provide some measure of the contributions made by the intrinsic nature of a confined polymer chain and the pervasive, cooperative, interchain interactions which can complicate the behaviour of bulk polymer samples. In the same way that dilute polymer solutions at the ® temperature have been effectively used to model disordered, bulk polymer phases (both glasses and melts), polymer ICs may be utilized to increase our understanding of the behaviour of polymer chains in their ordered, bulk phases, such as those found in crystalline and liquid-crystalline samples

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E.p.r. studies of cholestane (COL) and tempol (TPL) spin probes dissolved in mixtures Of two different side chain polymers and two different main chain polymers in the plasticizer dibutyl phthalate were performed. For each pair of polymers, one of the pair was considerably stiffer than the other due to its larger monomeric molecular weight. The studies demonstrated the existence of multiple relaxation times that were especially obvious at temperatures near Tso, i.e. the region intermediate between the fast and slow motion regimes. Arrhenius plots of relaxation times obtained from simulations of the observed spectra display many features previously reported for poly(vinyl acetate), including a gap or discontinuity in the COL data near Tso. In the present study, we showed that the spectra observed in the gap are sums of slow and fast spectra. Composite spectra, in which the fast portions of the observed spectra were subtracted out, were matched to spectral simulations. The relaxation times obtained in this way fell on the low temperature (slow motion) portion of the Arrhenius plots. Several features of the data appear to be associated with the stiffness of the samples and these features are examined.

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Copolymers based on substituted poly(vinyl chloride) (PVC) produced by reacting PVC with different thiolates in cyclohexanone solution and in the absence of solvent (melt), show different glass transition temperatures, T v for the same chemical composition. The variation of Tg for the vinylchloride-vinylthiobenzene, vinylchloride-vinylthiocresol and vinylchloride-vinylthionaphthoi copolymers obtained in the melt follows the Fox equation. However, the same copolymers obtained in cyclohexanone show a deviation from this trend of Tg as a function of molar composition. Factors such as microstructure, chemical composition distribution and molecular weight do not change appreciably from solution to the melt, and therefore cannot be responsible for these differences in the T~ values. We attribute the deviation in the Tg values of copolymers obtained in cyclohexanone solution to polymer-polymer interactions produced at local sites on the chain, and we propose that these interactions are related to chlorine atoms in isotactic and/or heterotactic triads

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Polypropylenes (PP) prepared with MgCI2/TiC14-EtaA1 and MgC12/TiC1Jbis(2-ethylhexyl)phthalate- Et3A1/Ph2Si(OMe)2 catalyst systems were fractionated by the temperature-rising elution fractionation method in the wide temperature range of -65 to 140°C. The fractionations were proved to take place mainly on the basis of isotacticity from the analyses of key fractions by 13C nuclear magnetic resonance, gel permeation chromatography, differential scanning calorimetry and X-ray diffraction. PP was shown to have a broad and continuous distribution of tacticity, ranging from nearly atactic to highly isotactic structures in the case of no electron donor system. The addition of electron donor, however, drastically reduced the amount of atactic and low isotactic PP, resulting in a very sharp tacticity distribution.

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The analysis of absorption and fluorescence spectra of poly(ether imide) solutions and related model compounds shows the existence of charge-transfer complexes in poly(ether imide) solutions and in poly(ether imide) solid state. A correlation is established between the fluorescence emission due to charge-transfer complexes and the aggregation state of poly(ether imide) solutions. The kinetics of aggregation of a solution and the aggregate dissociation phenomenon in dilute solution are observed from the study of fluorescence emission of poly(ether imide) solutions.

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