1992 рік

The mechanical and electrical properties of solution-processed poly (3-alkylthiophenes) with alkyl side-chain lengths of 6, 8 and 12 carbon atoms are discussed. Tensile drawing at elevated temperatures yielded oriented materials with moderately increased mechanical properties. A simple model accounting for defects in the regiospecificity, i.e. head-to-tail versus head-to-head or tail-to-tail monomer coupling, is introduced, in addition to side-chain dilution, to account for the low moduli of undoped samples. Doping with FeC13 • 6H20 led to significant enhancement of the mechanical properties of the drawn samples, as well as to high electrical conductivity. As was previously found for other conducting polymer systems, strong correlations were observed between mechanical properties and electrical conductivity. The conductivity was found to scale linearly with tenacity, independent of side-chain length

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The solution of the heat conduction equation with appropriate boundary and initial conditions makes it possible to determine the influence of the latent heat of fusion evolving during polymer crystallization on the temperature distribution near the crystallization front. It is shown that the increase in temperature at the crystallization front does not exceed a fraction of a degree.

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Elastic moduli El of crystalline regions in the direction parallel to the chain axis were measured by X-ray diffraction for poly(ether ether ketone) (PEEK), poly(ether ketone) (PEK) and poly(p-phenylene sulphide) (PPS). E l values of 71 GPa, 57 GPa and 28 GPa were obtained for PEEK, PEK and PPS, respectively. The calculated values for Treloar's method agreed well with these observed El values. These small E I values were considered to be due to the fact that the lengths of the arms where the moment of force acts during the deformation are longer for these polymers than for polyethylene (PE). The deformation through bond angle bending at hetero atoms played an important contribution to the extension of the chains. The difference in El values among these polymers was found to depend on the difference in the bond angles and their force constants. Elastic moduli E t of crystalline regions in the direction perpendicular to the chain axis were also measured for PEEK and PEK. These E t values were somewhat larger than those for PE; however, strong intermolecular interactions were not considered to act in these polymers. The intermolecular cohesive energy and heat resistance of these super engineering plastics were able to be evaluated through the measurement of E t values.

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The effect of thermal treatment on polypyrrole chloride and polypyrrole dodecyl sulphate has been studied. Changes in surface texture, electroactivity, composition and polarity after thermal treatment have been determined using scanning electron microscopy, cyclic voltammetry, fast atom bombardment mass spectrometry and gas chromatography, respectively

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Since membrane-bound macromolecules provide the most general and powerful mechanisms for biological ion sensing and ion channelling, a new type of polymer-modified electrode was designed: a multiphase material consisting of poly(styrene-co-acrylonitrile) and poly(L-glutamate) was synthesized as the block copolymer. The material has enabled polypeptides to be immobilized onto electrodes just by dipping. Electrochemical responses towards Ca 2 ? were obtained based on the permeability change of the redox-active species as the indicator. The modified electrode has remarkable stability due to the vinyl polymer chains which serve as building blocks of the membrane.

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Crosslinking of nitrile rubber (NBR) and poly(vinyl chloride) (PVC) can be accomplished separately using ethylenethiourea (ETU) with and without the presence of sulphur (S) respectively. ETU/S combination in appropriate doses brings about ready co-crosslinking of NBR and PVC in their blends. Comparative studies of the curing characteristics of some NBR-PVC blends and some important physical properties of the blend vulcanizates have been made using the test curative (ETU/S system) and a conventional curative (tetramethylthiuram disulphide (TMTD)/sulphur (S) system). The ETU/S curative system produces crosslinking effects which in some respects are comparable with, and in some other respects are even substantially better than, those produced by the conventionalTMTD/S curative system, particularly with respect to consequential curing parameters and blend vulcanizate properties including morphological patterns and ageing behaviour.

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Orthophthalic polyester, isophthalic polyester and vinyl ester resins exposed to water and to saturated salt solutions at 40, 65 and 90°C were studied to determine if disc cracks formed. The time of initiation of disc cracks was determined and related to the water absorption curves. The morphology was studied by optical and scanning electron microscopy. Disc cracks were found in orthophthalic and vinyl esters but not in isophthalic resins. The two-component phase diagram of polymer and water is the key to the prediction of behaviour. A new mechanism for disc crack initiation is presented. It states that disc cracks are the result of a thermodynamically driven phase separation that results in nucleation of a water phase within a supersaturated polymer. The mechanism is supported by the observation that, when the temperature of a nearly, but not completely, water-saturated polymer is reduced, bringing the polymer in to a region of supersaturation, massive disc crack initiation results. The reverse process--the disappearance or healing of disc cracks--predicted by the phase diagram and reported earlier in the literature, was confirmed in this work when a water-saturated, heavily disc-cracked specimen was placed into an environment of lower relative humidity. The growth rate and ultimate coalescence of disc cracks depend on the nature of the polyester. The hydrolysis of the polyester by the disc crack liquid with chain breakdown by de-esterification at the water-polymer interface is a key step in blister formation. It results in a concentrated solution, which generates osmotic pressure. The orthophthalic polyester is susceptible to hydrolysis; the other two resins are more resistant. Examples are noted of disc crack formation in polymers not saturated. This is explained by the presence of a water-soluble second phase, which was present initially or is generated in the polymer during heat treatment. The ability of the water-polymer phase diagram to predict the appearance and disappearance of disc cracks strongly supports the interpretation of disc cracking as a thermodynamic process.

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Literature data and unpublished results have been used to correlate the primary and secondary structures of gellan, welan, rhamsan, succinoglycan and galactoglucan in solution with their rheological properties. In dilute solution the chain conformation ranges from that of the random coil of galactoglucan to that of the stiffer double helix of gellan, and possibly a similar conformation exists for welan and rhamsan. In semidilute solution the rheological behaviour of the above microbial polysaccharides is mainly determined by their conformation in solution. Ordered regions along the polysaccharide chains seem to be the prerequisite to establish intermolecular interactions which lead to non-transient polymer networks. The lack of ordered secondary structure leads to entangled networks in which the topological constraints govern the rheological behaviour. Experimental evidence is reported to support the hypothesis that the chain conformation and rigidity can be qualitatively predicted on the basis of rheological measurements

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A chemical analog of poly(vinyl phenol) mixes exothermically with analogs of polyacetal and poly(ethylene oxide), suggesting miscibility in the case of blends of poly(vinyl phenol) with polyacetal and with poly(ethylene oxide). The interaction parameter corresponding to the poly(vinyl phenol) and the poly(ethylene oxide) analog mixtures agrees well with an interaction parameter reported for the polymer mixtures, which was based on the melting point depression of poly (ethylene oxide ) in blends with poly (vinyl phenol). FTi.r. spectroscopy indicates the presence of strong hydrogen bonding between phenol and ether groups in these analog mixtures. Application of the binary interaction model predicts that a rather wide range of styrene-vinyl phenol copolymers would exhibit miscibility with polyacetal.

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Poly(dimethyl phosphazene) displays, upon crystallization, a polymorphic behaviour showing two crystalline modifications, form I with a chain periodicity of 4.9/~, and a melting point of 146°C and form II with a chain periodicity of 5.85/~ and a melting point of 76°C. Form I, the only crystalline modification that is observed upon melting and recrystallization, has been completely characterized from a structural point of view through the study of X-ray diffraction patterns from oriented fibres and powder samples. A final structural refinement was carried out with the Rietveld method. The unit cell is monoclinic, space group P21/c and the cell parameters are a = 6.345(2), b = 13.805(4), c = 4.887(2)/~,//= 110.45(3) °.

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