Structure and morphology of ethylene-vinyl chloride copolymers

A series of ethylene--vinyl chloride copolymers with a sequence distribution toward the alternating side of random and a wide range of comonomer content (up to 37.3 mol% vinyl chloride) have been examined in the solid state by diffraction and microscopic techniques and high-resolution exp 13 C NMR spectroscopy. Significant expansion of the unit cell in the alpha dimension, observed as the amount of Cl 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 pseduohexagonal. Differences in the chemical shifts of crystalline and amorphous CH(Cl) resonances, togetther with differences in their mobilities (T sub 1 ) as observed by solid-state exp 13 C NMR spectroscopy, corroborate the incorporation of Cl inside the crystal. Comparison of quantitative exp 13 C NMR spectra at temperatures above and below the melting point indicates that at least 20% of the Cl resides inside the crystal. The irregular distribution of Cl in the 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 up to 2.4 mol% Cl content. For higher Cl contents, the crystals become increasingly more disordered and defective but retain an essentially lamellar character for copolymers with up to 21.2 mol% Cl. , , . 49 ref.--AA