1992 рік

The structure of initial and ultimate chain units in polybutadiene and polyisoprene was studied by means of 2H nuclear magnetic resonance spectroscopy. Polydienes were prepared with a neodymium catalyst; quenching was performed with deuteromethanol. The enrichment of quenched ultimate units by trans-l,4 structures at the expense of cis-l,4 structures at high polymer yields was observed. When using diisobutylaluminium deuteride DAI(i-Bu)2, as chain transfer agent, it was shown that the principal site of chain transfer reaction was the A1 D bond. The initial unit of polybutadiene was predominantly of trans-l,4 structure.

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The toughening of nylon-6 using triblock copolymers of the type styrene-(ethylene-co-butylene)-styrene (SEBS) and a maleic anhydride (MA) functionalized version (SEBS-g-MA) is examined and compared with a conventional maleated ethylene/propylene elastomer. The changes in rheology, adhesion, crystallinity, morphology and mechanical behaviour associated with the reaction of the anhydride with the nylon-6 are documented~ Combinations of the SEBS and SEBS-g-MA elastomer blends with nylon-6 give higher levels of toughening than is achieved with the functionalized elastomer alone. The particles of pure SEBS were about 5/~m in diameter (too large for toughening nylon-6), whereas SEBS-g-MA alone yielded particles of about 0.05/~m (apparently too small for optimal toughening). Combinations of the two types ofelastomers gave a continuously varying particle size between these extreme limits. This suggests that the two rubbers form essentially a single population of mixed rubber particles. The order of mixing did not significantly affect the mechanical properties of these ternary blends. The evidence for maximum and minimum rubber particle sizes that can be effective for toughening nylon-6 is discussed.

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The influence of oxygen on polymerization kinetics in photopolymer films is studied using a fluorescence-based technique developed in this laboratory. Fluorescent N-vinylcarbazole monomer is used to monitor photopolymerization kinetics in the presence and absence of oxygen. Effects of oxygen at pressures up to 3 atm (3 x lo5 Pa) on photopolymerization in various inert polymer matrices are studied. A reduction in the photopolymerization rate without induction period is observed in the presence of oxygen. A detailed computer analysis of the kinetics is presented. The unusual polymer spatial distribution is calculated and attributed to the anisotropy of illumination and the diffusion and reaction of the mobile oxygen and monomer species.

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A new experimental technique, 'polarization-modulated laser Raman scattering' (PMLRS), is presented for the study of the dynamics of polymeric materials subjected to transient flows. A detailed analysis of the experiment based on Jones-Mueller matrix calculus is presented. Jones and Mueller matrices that take into account the integrated effect of the deformed sample's birefringence are developed for a Raman scattering element, using either the 0 ° or 180 ° scattering geometries. To test the predictions of the theory a Raman scattering system, based on high-speed phase modulation (50 kHz) of the incident light coupled with phase-sensitive detection, has been developed. This system is also capable of simultaneously measuring birefringence. Single-step reversal extension and step strain experiments were conducted using a polyisobutylene melt. Experiments were done using the Raman scattered light associated with the v stretching vibration of C-H groups present in the specimen. The results obtained indicate that the Raman signal ratios all depend on the second- and fourth-order moments of the orientation distribution function of polymer segments and on the sample's birefringence

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The structure of initial, ultimate and inner chain units in polybutadiene produced with NdCIa. 3 (i-PrOH)-HAI (i-Bu)2 was studied by means of 13C nuclear magnetic resonance spectroscopy. Initial units are shown to be predominantly of trans-CHaCH=CHCH2- structure. Conversely, 90% of inner units have ?is configuration. Ultimate units obtained by quenching with H20 (D20) are predominantly of 1,2 structure. On the basis of the data obtained, the polymerization mechanism was discussed.

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The toughening of nylon-6,6 using triblock copolymers of the type styrene-(ethylene-co-butylene)-styrene (SEBS) and a maleic anhydride (MA) functionalized version (SEBS-g-MA) is examined and compared with the behaviour reported for nylon-6 in the accompanying paper. Nylon-6,6 can be made super-tough by blending with SEBS-g-MA, and addition of SEBS merely reduced toughness. For nylon-6 super-toughness was achieved only with certain combinations of SEBS and SEBS-#-MA since with just the latter the rubber particles (~ 0.05/~m) generated were too small for effective toughening. The SEBS served to raise particle size to within the optimal range. In contrast, blends of nylon-6,6 with SEBS-g-MA give rubber particles that are within the optimal size range (just less than 1/~m); however, these particles have a very complex structure. For blends containing both SEBS and SEBS-g-MA, there seem to be two distributions of shapes but not size. Evidence is shown that the extent of grafting to nylon-6,6 is less than that in nylon-6 for similar conditions. It is proposed that the large difference in morphology found for nylon-6,6 versus that for nylon-6 stems from basic chemical differences between the two polyamides rather than rheological or processing factors. Nylon-6 is monofunctional while nylon-6,6 is difunctional in their reactions with anhydride. The possible consequences of this are discussed.

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Conducting polypyrrole films with p-toluenesulphonate, perchlorate and tetrafluoroborate dopants were aged at elevated temperatures in oxidizing and inert environments. Their decline in electrical conductivity was analysed using a first-order decay model. Films were also examined by X-ray photoelectron spectroscopy, differential scanning calorimetry, thermogravimetric analysis and scanning electron microscopy. Changes in polymer morphology, degree of oxidation and dopant integrity were determined.

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We report morphological studies of solvent-cast polymer blend films containing a polystyrene/poly (methyl methacrylate) (PS/PMMA) block copolymer with polymers that are miscible with one block copolymer segment, viz. polystyrene (PS), random styrene/acrylonitrile copolymers (SAN) and poly(methyl methacrylate) (PMMA). By utilizing SANs that have four different acrylonitrile (AN) contents, we vary the enthalpic interaction between the SAN copolymer and the block copolymer segments. With polystyrene as the minor constituent, and for a given overall composition ratio and specified molecular weights of the blend components, the morphology of the blends was found to change systematically from dispersed spheres to cylinders, vesicles and lamellae, depending on the strength of the enthalpic interaction between the matrix and the block copolymer segments. Selective staining of the PMMA block at the interphase in blends containing SANs was possible only for SANs of higher AN content. This is interpreted as an indication of interfacial microsegregation of the PMMA block from the SAN matrix as the AN content increases. These morphological changes can be explained by differences in the relative solubility of matrix polymer in the micellar corona, which are controlled by the balance between attractive and repulsive interactions with the miscible and immiscible blocks.

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The feasibility of using e.p.r, spectrscopy in studying conformations of spin-labelled macromolecules in the amorphous solid state is examined. The algorithm for e.p.r, spectra computation is developed. It was assumed that molecular weights of labelled linear chains are high and their solid solution is diluted. It is shown that the scaling exponent which determines the dependence of mean-square end-to-end distance on molecular weight and stiffness parameter (mean-square length of monomer unit) may be extracted from the spectra. Computed spectra are compared with experimental ones, measured at 77 K, of diluted solutions of spin-labelled poly(4-vinyl pyridine) [P(4-VP)] of different molecular weights in methanol and non-labelled P(4-VP). The conformational state (Gaussian coil), parameter of stiffness, and radius of gyration of spin-labelled P (4-VP) macromolecule in frozen solutions are determined. A conclusion is drawn that e.p.r, spectroscopy may become a new tool for studying chain conformatin in solid polymers.

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The effects of molecular weight and block length ratio on the rheological behaviour of polystyrene-block-polyisoprene-block-polystyrene (SIS) copolymers in the disordered state were investigated. For the study, SIS triblock copolymers were synthesized via anionic polymerization, and linear dynamic viscoelastic properties (i.e. dynamic storage and loss moduli, G' and G") of the SIS block copolymers were measured at various temperatures as functions of angular frequency (to), using a cone-and-plate rheometer. The disordered state of the samples was determined by the threshold temperature at which the plot of log G' versus log G" becomes virtually independent of temperature as the temperature was increased. It has been found that when the block length ratio is kept the same, the melt elasticity of SIS block copolymers in the disordered state becomes independent of molecular weight, while the viscosity increases with molecular weight, and the block length ratio greatly influences both melt viscosity and elasticity

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