1993 рік

Optically active poly(7-ketosulfide)s containing the (2R,3R)-l,4-dimercapto-2,3-butanediol moiety were reacted with butyraldehyde to obtain the corresponding acetalized derivatives. The optically active low-molecular-weight analogues were also similarly prepared. High- and low-molecular-weight products were characterized by spectroscopic methods and chiroptical techniques. The conformational and stereochemical features of the macromolecules, as compared with the polymeric precursors as well as the low-molecular-weight analogues, are discussed on the basis of nuclear magnetic resonance (n.m.r.) and circular dichroism measurements. In particular, n.m.r, data indicate that the acetalization reaction does not appreciably modify the diastereomeric distribution of the constitutional repeating units and circular dichroism spectra confirm the presence of asymmetric induction on the chromophoric groups, although no evidence is found of structurally ordered conformations having one largely prevailing single chirality.

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The logarithm of the surface resistivity, log(SR), for a poly(ether sulphone)/carbon-fibre composite ranged between 6.23 and 10.66, depending on the conditions of moulding. The statistically significant variables were: the injection pressure, P~; the temperature of the mould, Tmould; and the temperature of the barrel, Tbarrel. The fibre lengths and distributions in the samples moulded under the extreme conditions for Tmou~d and P~ were not significantly different from each other--at 126pm and median lengths at 100-110 /~m. However, the lengths of the fibres at the surface of these samples, shorter than those in the centre, were slightly longer for the more conductive sample, which was moulded at maximum settings of both P~ and Tmou~d: the average fibre length was 114 + 77 pm and median 90-100/~m for the more conductive sample, compared with 109___ 82/~m and median 80--90#m for the sample moulded at minimum settings of P~ and Tmou~o. The trend in relative concentration of the fibres at the surface for these samples was consistent with that in the log(SR); the sample with lower SR had a slightly higher concentration of fibres from the surface through a depth of approximately 500#m. We propose a physical model whereby the content of fibres at the surface and their length influence the surface resistivity. Although the orientation of the fibres has the potential to influence the surface resistivity of the composites, there was no significant difference in orientation for samples examined in this study.

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Copolymerization of cyclohexyl acrylate (CHA) with styrene (Sty) and N-vinyl-2-pyrrolidone (VPD) was carried out in benzene and dioxane at 70°C and 75°C, respectively, using benzoyl peroxide as initiator. The copolymers were characterized by i.r., IH n.m.r., g.p.c, and viscometry. The compositions of the copolymers were determined by elemental analysis and the reactivity ratios were computed by Fineman-Ross, Kelen-Tudos and extended Kelen-Tudos methods, rcH A =- 0.272_ 0.048, rSty = 0.913 _ 0.107 for CHA-Sty system and rCH A = 1.297 +0.088, rvpD=0.122 +0.014 for CHA-VPD system are determined by extended Kelen-Tudos method. The Q and e values for CHA monomer were also determined.

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Fourier transform infra-red spectroscopy coupled with photoacoustic detection (PA FTi.r.) has proved to be a useful tool for finding out about quantitative structural changes in solid materials. Poly(ethylene terephthalate) (PET) is a well known semicrystalline polymer that shows important changes on annealing. In order to obtain a complete picture of isomer distributions in industrial PET samples, spectroscopic measurements were correlated with differential scanning calorimetry (d.s.c.). The results obtained indicate that the structural characteristics of the thermally treated samples are related to the fabrication process. Two different strata in the plates can be distinguished: a skin layer and the core. The correlation between the apparent degree of crystallinity of the surface obtained by d.s.c, and the percentage of trans isomer obtained by PA FTi.r. allows the latter parameter to be separated into crystalline and amorphous trans isomer and to follow its evolution with the annealing process. Amorphous trans isomer vanishes at the primary isomerization (~ 100°C) while crystalline trans and gauche conformations show sigmoidal evolution. At higher annealing temperatures (> 140°C) the ordered trans conformation shows an approximately linear increase at the expense of the gauche conformation. Finally, a direct correlation between the ordered trans isomer and the apparent degree of surface crystallinity can be made.

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The structures displayed by poly{10-[(4-cyano-4'-biphenyl)oxy]decanyl vinyl ether} were studied by small- and wide-angle X-ray scattering. It is shown that this polymer possesses two different smectic phases : an ordered smectic E phase at low temperatures, and a smectic A phase at higher temperatures. The smectic A phase is characterized by a double-layer packing with partial overlap of the cyanobiphenyl groups, while the ordered smectic E phase displays a layer packing characterized by the presence of two incommensurate periodicities. The structural rearrangements accompanying the phase transformation from the ordered to the disordered smectic phase are discussed in detail.

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Certain biscyanamides were synthesized by reacting aromatic diamines with cyanogen bromide. They were used as starting materials for preparing a new series of N-cyano-substituted homopolyamide and copolyamides. Homopolyamide was prepared from the reaction of terephthaloyl dichloride with 4,4'-biscyanamidediphenylmethane. Various copolyamides were prepared by reacting terephthaloyl dichloride with a mixture of an aromatic diamine and the corresponding biscyanamide. The polycondensations were carried out in solution at low temperature in the presence of acid acceptor. In addition, a model compound was synthesized from the reaction of 4,4'-biscyanamidediphenylmethane with a double molar amount of benzoyl chloride. The polyamides were characterized by FTi.r. and IH n.m.r. spectroscopy as well as by inherent viscosity measurements. The modified polyamides showed higher solubility in common solvents than the corresponding unsubstituted polyamide. Crosslinked polymers were obtained by curing the N-cyano-substituted polyamides. Their thermal stability was correlated with the curing conditions as well as the concentration of cyano groups. The cured modified polyamides were stable up to 317-370°C in N 2 or air and afforded anaerobic char yield of 45-58% at 800°C.

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Blends of polycarbonate (PC) with ABS (acrylonitrile-butadiene-styrene) materials have commercially useful properties without requiring a compatibilizer, which is necessary for most other commercial multiphase blends. It has been proposed that this is due to a favourable thermodynamic interaction between PC and the styrene-acrylonitrile (SAN) copolymer matrix of ABS. A variety of evidence suggests this interaction is optimum at about 25 wt% acrylonitrile, which is roughly the composition of the azeotrope and of most commercial materials. A critical molecular weight analysis of the phase behaviour of PC-SAN blends is presented here, which leads to a quantitative estimate of the interaction energy that is consistent with available facts. When the molecular weights of the PC and SAN components are reduced to about 3000 each, their blends become miscible and the observed phase behaviour allows calculation of interaction energies in terms of a binary interaction model using both the Flory-Huggins and the Sanchez-Lacombe equation of state theories. End-group effects were accounted for as necessary. The estimated interaction energy is a refinement of a previous estimate based on the phase behaviour of copolycarbonates and SAN copolymer blends. The current estimate allows prediction of interfacial tensions that are consistent with morphology observations for PC-SAN blends presented here and elsewhere. It also predicts that the extent of partial miscibility is very limited and should produce very small shifts in the glass transitions of the components when blended as observed here and by others for purified SAN materials. Prior claims to the contrary result from partitioning between the phases of oligomers in commercial SAN copolymers.

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A tension-torsion combined stress was loaded onto cylindrical rods of polyethylene to investigate the deformation mechanism of the crystalline phase under non-uniform stress. On applying the combined stress, a neck occurred at the centre of the sample and extended in the axial direction. After necking occurred, the twist deformation generated compressive stress in the radial direction, which suppressed the formation of micro-voids. Wide-angle X-ray diffraction revealed the following facts. The c axis, i.e. the crystal molecular chain axis, deviates from the axial direction owing to the combined loading of the tensile force and the shear force. The b axis, which is the long axis of the initial lamellae, orients selectively in the radial direction in the non-uniform stress state in which the shear stress increases in proportion to the distance from the centre of the cylindrical rod.

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The morphologies of three low-molecular-weight poly(styrene-b-isoprene) diblock copolymers and their blends with homopolystyrene (hPS) at 66 vol% styrene have been investigated. Addition of hPS to one copolymer produces lamellar-catenoid or double-diamond morphologies, depending on hPS chain length. In another blend, microstructural disorder arises

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Melt-blended polysulfone (PSF) and poly(phenylene sulfide) (PPS) are notch sensitive. A significant improvement in the notched Izod impact toughness occurs when at least 10 wt% of a shell-core rubber modifier is incorporated into the blend. At rubber modifier levels above 15 wt%, the notched Izod impact strength was essentially retained upon annealing at 160°C for 2 h, while below 15 wt% of rubber modifier, the notched Izod impact strength decreases after annealing under the same conditions. Izod impact fracture surface morphology was studied using scanning electron microscopy (SEM). Fracture surfaces without a rubber modifier exhibit cavitation around the dispersed phase, i.e. PPS. On the other hand, fracture surface morphology of the rubber toughened blends with the same PSF/PPS composition show no cavitation surrounding the dispersed phase. Blend morphology was also studied using transmission electron microscopy (TEM).

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