1993 рік

13 C n.m.r, spectroscopy was used to determine the microstructure of naphthalene-containing polymers obtained by free radical polymerization. The splitting of the various carbon resonances of poly(1-naphthyl methacrylate) (PNMA), poly(1-naphthylmethyl methacrylate) (PNMMA) and poly[2-(1-naphthyl)ethyl methacrylate] (PNEMA) show that these are heterotactic polymers conforming with Bernoullian statistics. Based on the calculated probability of generating a meso sequence at the end of the growing chain, the isotacticity appears to decrease in the sequence PNMA > PNMMA ~ PNEMA. These results are discussed in relation to the photophysical behaviour of these polymers.

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The courses of crystallization and of demixing or mixing, respectively, can interfere and compete in polymer blends with a miscibility gap. Crystallization dominates at lower temperatures, possibly inhibiting rejection of the non-crystallizing component into the remaining melt and enhancing its concentration in the amorphous regions between the crystalline domains. Time-resolved small-angle X-ray scattering measurements on poly(e-caprolactone)/polystyrene (PCL/PS) blends, this system exhibiting an upper critical solution temperature, reveal that the amorphous regions between the lamellae within the PCL spherulites nearly do not phase separate when passing the binodal composition. Instead, supersaturation of composition occurs. The initially bent lamellae flatten with time, and the supersaturated spherulite amophous phase post-crystallizes according to the insertion crystallization scheme on a timescale that is comparable to the overall crystallization rate.

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Molecular modelling calculations have been used to explore the unexpectedly large values of crystallinity measured in atactic poly(vinyl chloride) (PVC) and polyacrylonitrile (PAN). Using MOPAC V:AM1 (distributed by QCPE), it was found that not only can a chain of isotactic PVC (and PAN) emulate the shape and axial repeat of an equivalent (planar zigzag) syndiotactic molecule, but that the shape-emulating conformation has its own energy minimum. This conformation is similar to that first suggested by Juijn. It appears that the dipole interactions between adjacent hydrogen and chlorine atoms are able to stabilize this conformation even though there is no minimum apparent on a two-dimensional energy map corresponding to one repeat unit. Calculations on longer sequences show that this conformation has a subsidiary energy minimum. Similar behaviour has been found in the case of PAN. Wide-angle X-ray diffraction from PVC crystals composed of syndiotactic and isotactic monomer units (but using established unit cell dimensions) was simulated using CERIUS (Molecular Simulations Ltd, Cambridge, UK). The crystalline component of the experimental diffraction profile was found to correspond to that calculated for a mixed tacticity lattice. Furthermore, the relative intensities of the 200 and 110 diffraction maxima have been shown to give a good indication of the mean chain tacticity within the crystallites which can be related to the overall tacticity of the polymer. Calculations of crystallinity content based on mixed tacticity lattices (where dyad tacticity = 0.55) were found to be consistent with the crystallinity and crystallite thickness observed experimentally (10% and 33 A), whereas these observations are quite inexplicable if the only crystallizable sequences are syndiotactic. A similar predicted relationship between lattice tacticity and relative intensity of the 200 and 110 peaks could not be confirmed for PAN as the almost pseudo hexagonal chain packing means that the 200 and i10 peaks are all but superimposed in the experimental plots. It is noted that extra low angle reflections are found in the simulations of mixed tacticity crystallites where the models are not large enough to ensure a completely random distribution of the isotactic, shape-emulating sequences, if they have been arranged with any degree of periodicity. Low angle reflections have also been observed experimentally. Hence, although PAN does not have the 200/110 WAXS fingerprint of PVC, there is, in addition to the general observation of high crystallinity for the atactic polymers, experimental evidence for co-crystallization of the configurational isomers

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Results of equilibrium stress-strain experiments and Fourier transform infra-red measurements of segmental orientation, previously reported for moderately crosslinked cis-polyisoprene networks by Amram et al. (Polymer 1986, 27, 877), are extended to networks with high degrees of crosslinking. The samples were stretched to the limit of maximum chain extensibility. The absence of strain-induced crystallization during experiments was inferred from infra-red measurements, according to which the 844 cm- 1 absorption band specific to crystalline regions did not exhibit any systematic shift in one direction. The reduced force versus inverse extension ratio showed strong upturns while the reduced orientation curves did not exhibit any upturns. Likewise, the analogue of the stress optical coefficient, defined as the ratio of molecular orientation to true stress, exhibited a strong decrease with extension, in contrast to Gaussian networks in which it is approximately independent of the degree of deformation.

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The effect of trifluromethyl group substitution on the thermal properties of blends of a polyaramide with several aliphatic polyamides has been determined. Miscibility of the substituted polyaramide with nylons 46, 6, 66, 69, 610 and 11 was shown by the existence of single, composition-dependent glass transition temperatures (Tgs) and composition-dependent crystalline melting temperatures (T=s). The results are discussed with reference to Tg and Tr~ predictive equations.

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The thermal diffusivity D and the relative heat capacity HC were measured for poly(vinylidene fluoride)/poly(methyl methacrylate) (PVDF/PMMA) blends by flash radiometry. The effect of the crystal form on D of these polymer blends as well as the dependence of O and HC on temperature were discussed. In the PVDF content region between 70 and 80 wt%, the blend samples preferentially form the crystal phase when they are prepared by melt quenching. The dependence of D on PVDF content for the melt-quenched sample showed a noticeable change in the composition region in which the//crystal phase is formed. D decreased with increasing PVDF content up to 70 wt% and then increased up to 100 wt%, showing a peak between 75 and 80 wt%. From the X-ray diffraction patterns, the crystallinity of the blends monotonically decreases with decrease of PVDF content. The results imply that the peak in D in the melt-quenched 75/25 and 80/20 PVDF/PMMA blends is not related to the crystallinity but to another structural factor. The temperature profile of D showed inflection points corresponding to the glass transition temperature and the melting temperature of the :t crystal phase. The temperature profile of HC exhibited changes of HC due to the melting transition of the ~ and ~ crystal phases. These points from the temperature profile of D and HC correspond well to those from thermal analysis.

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Polyblend fibres were made of polypropylene (PP) and three thermotropic liquid crystal polymers (LCPs). The LCPs were found to exist in different morphological structures; the Vectra A900 and Vectra B950 LCPs existed mainly as fibrils, while the Rodrun LC3000 existed as short elongated ribbons. The tensile properties of the as-spun fibres were improved on addition of the LCPs, with the properties of the drawn polyblend fibres varying with the drawing procedure. In one-stage drawing, the polyblend fibres gave poorer tensile properties than the pure PP fibre. However in two-stage drawing, the Vectra A900 blend showed an increase in initial modulus over that of the pure PP fibre, while the Rodrun LC3000 blend produced an improvement in fibre tenacity.

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The charge transfer (CT) interactions and molecular structures involving poly(2-vinylpyridine) (P2VP) and poly(4-vinylpyridine) (P4VP) and various halobenzoquinone acceptors have been studied by X-ray photoelectron spectroscopy (X.p.s.). X.p.s. results suggest that the CT interactions have proceeded beyond the pure formation of molecular CT complexes. The structures of the CT complexes derived from the X.p.s. results are further confirmed by the static secondary ion mass spectrometry (s.i.m.s.) data. The fragmentation patterns of the CT complexes are consistent with the presence of linkages between the pyridinium nitrogens and the various acceptors.

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Results of Fourier transform infra-red (FTi.r.) dichroism measurements of segmental orientation in model poly(dimethylsiloxane) (PDMS) networks of different molecular weights between junctions are interpreted in terms of the constrained junction model of rubber elasticity. The theory shows quantitative agreement with experimental data, without the necessity of adjusting any parameter. Based on this agreement, one may conclude that in PDMS networks, the dependence of orientation on deformation results from the non-affine transformation of junction points, and that local intermolecular contributions to segmental orientation are not significant. In the case of less flexible chains such as polyisoprene on the other hand, intermolecular contributions to segmental orientation might be relatively more important. Correspondence between birefringence experiments and segmental orientation is formulated which permits direct quantitative comparison between the birefringence and FTi.r. dichroism experiments.

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The glass transition temperatures (Tgs) of binary blends of poly(p-vinyl phenol) with poly(methyl methacrylate), poly(ethyl methacrylate) and poly(ethyl methacrylate-co-methyl methacrylate) have been determined. The experimental T~-composition data do not obey the Couchman-Karasz equation. However, the Gordon-Taylor, the Kwei and the Schneider equations fit the experimental data quite well. The values of the Gordon Taylor k parameters, as well as the measurements of the glass transition widths, suggest a similar average intensity of the specific intermolecular interactions in the systems studied here, which is in agreement with the Fourier transform infra-red results. The Kwei and the Schneider equations are able to reflect the additional stabilization due to the dilution of copolymer repulsive interactions in the poly(p-vinyl phenol)/poly(ethyl methacrylate-co-methyl methacrylate) blends

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