The solid state structure and properties of homogeneous copolymers of propylene and 1-hexene were studied by examining melting behavior, dynamic mechanical response, and morphology primarily with atomic force microscopy, wide- (WAXS) and small-angle X-ray scattering, and tensile deformation. Chain microstructure was analyzed by 13C NMR. The results indicate that copolymers used in this study have an essentially random distribution of comonomer. For copolymers with less than 10 mol% hexane, crystallinity decreases with increasing comonomer content, as expected for exclusion of comonomer from the polypropylene crystal. The peak melting and crystallization temperatures also decrease with increasing hexene content. Copolymers with more than 10 mol% hexane crystallize with a new crystal structure that permits incorporation of hexene units. This is inferred from a higher level of crystallinity than would be expected if comonomer were excluded from the crystal and better development of the crystals as the hexene content increases. Copolymers with the new crystal structure crystallize slowly. After an incubation period, long fibrous lamellae form sheaf-like arrays that develop into small spherulites. The corresponding enthalpy change as a function of time assumes an S-shape characteristic of a phase transition described by the Avrami process. The new crystallographic form has not been reported for either polypropylene or for poly(1-hexene). It follows from WAXS studies of highly oriented films that the crystallographic unit cell has orthorhombic symmetry with a = 1.9860 nm, b = 1.7176 nm, and c = 0.6458 nm. The most intense diffracting planes are identified as the (210) plane reflecting at 2θ = 10.30°, the (230) plane reflecting at 2θ = 17.65°, the (040) plane reflecting at 2θ = 20.60°, the (031) plane reflecting at 2θ = 20.73°, and the (112) plane reflecting at 2θ = 28.52° for Cu Kα radiation. On the basis of pole figures, it is evident that the easiest slip during plastic deformation of the new crystal form occurs along (0k0) planes.

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SYNOPSISDifferential scanning calorimetry (DSC) was used to analyze the crystal distribution in homogeneous ethylene-octene copolymers polymerized by the constrained geometry catalyst technology (CGCT). To minimize ambiguities from thermal history effects, copolymers were isothermally annealed at temperatures within the melting range. The cumulative crystallinity was related to the crystal distribution by the Gibbs-Thomson equation. The results provided a clear distinction between Type I copolymers (density less than 0.89 g/ cc) and Type I1 copolymers (densities between 0.89 and 0.91 g/cc). The former had a singlecrystal population that was identified with the bundled crystals seen in transmission electron micrographs. In comparison, the latter had two crystal populations that correlated with lamellar crystals and bundled crystals. 0 1995 John Wiley & Sons, Inc.

ABSTRACT:The improvement in oxygen barrier properties of poly(ethylene terephthalate) (PET) by incorporation of an impermeable phase such as crystallinity or talc platelets was examined. Crystallinity was induced by crystallization from the glassy state (cold crystallization). Microlayering was used to create talc-filled structures with controlled layer architecture. The reduction of permeability in crystallized and talcfilled PET was well described by Nielsen's model. Changes in permeability of crystalline PET could not be ascribed to the filler effect of crystallites only. Our data on solubility, obtained on the basis of measurements of the oxygen transport coefficients, confirmed a previous finding that the amorphous phase density of PET decreases upon crystallization. The data were amenable to interpretation by free volume theory. Talc-filled materials processed by different methods showed the same permeability; however, much better mechanical properties were achieved by microlayering.

ABSTRACT:Composites that incorporate a conductive filler into an ethylene-octene (EO) elastomer matrix were evaluated for DC electrical and mechanical properties. Comparing three types of fillers (carbon fiber, low structure carbon black, and high structure carbon black), it was found that the composite with high structure carbon black exhibited a combination of properties not generally achievable with this type of filler in an elastomeric matrix. A decrease in resistivity at low strains is unusual and has only been reported previously in a few instances. Reversibility in the resistivity upon cyclic deformation is a particularly unusual feature of EO with high structure carbon black. The mechanical and electrical performance of the high structure carbon black composites at high strains was also impressive. Mechanical reinforcement in accordance with the Guth model attested to good particle-matrix adhesion. The EO matrix also produced composites that retained the inherent high elongation of the unfilled elastomer even with the maximum amount of filler (30% by volume). The EO matrix with other conducting fillers did not exhibit the exceptional properties of EO with high structure carbon black. Composites with carbon fiber and low structure carbon black did not maintain good mechanical properties, generally exhibited an increase in resistivity with strain, and exhibited irreversible changes in both mechanical and electrical properties after extension to even low strains. An explanation of the unusual properties of EO with high structure carbon black required unique features of both filler and the matrix. The proposed model incorporates the multifunctional physical crosslinks of the EO matrix and dynamic filler-matrix bonds.