Structure and Morphology of Ethylene-Vinyl Chloride Copolymers.

A series of ethylene-vinyl chloride copolymers with a ``random- like'' sequence distribution and a wide range of comonomer content have been examined in the solid state by diffraction and microscopic techniques and high resolution sup (13) C NMR. Significant expansion of the unit cell in the a dimension observed as the amount of chlorine in the copolymer increases indicates a significant incorporation of the Cl substituents inside the crystal. X-ray diffraction also shows progressive intermolecular disorder with increasing vinyl- chloride content, resulting in a change in the packing of chains from orthorhombic to pseudohexagonal. Differences in the chemical shifts of crystalline and amorphous CH(Cl) resonances, together with differences in their mobilities (T sub 1's) as observed by solid state sup (13) C NMR, corroborate the incorporation of Cl inside the crystal. Comparison of quantitative sup (13) C NMR spectra at temperatures above and below the melting point indicates that at least 20% of the Cl's reside inside the crystal. The irregular distribution of chlorine in our copolymers also affects their morphology. Electron microscopy showed the lamellar characteristics to progressively depart from those of polyethylene, although the preferred growth direction and the molecular chain axis tilt within the crystals are preserved for the copolymers with the lowest Cl contents.