Thermal transitions of ethylene‐vinyl chloride copolymers and their blends

Abstract

Differential Scanning Calorimetry (DSC) measurements were performed on a series of ethylene‐vinyl chloride copolymers (E‐V) prepared via reductive dechlorination of poly(vinyl chloride) with tributyltin hydride. The copolymers were identical in chain length and branching distribution; differing only in comonomer content, sequence distribution, and stereoregularity of adjacent —V— units. Extrapolation of glass transition temperatures, Tg, measured for our E‐V copolymers to pure polyethylene (PE) predicted a Tg = −85 ± 10°C for amorphous PE. E‐V copolymers with greater than 60 mol percent —E— units exhibited melting endotherms from 20 to 128°C and degrees of crystallinity from 12 to 63 percent. The melting point depressions observed for our E‐V copolymers were in agreement with Flory's theory, if the CH2CH2 moiety is considered to be the crystallizable unit and the moiety is assumed to prevent the CH2CH2 units attached on either side from being incorporated into the crystal. In general, the E‐V copolymer blends with PE were incompatible, while those with PVC were compatible only for E‐V copolymers with high V contents (>80 mol percent). Blends of the amorphous E‐V copolymers were found compatible if their V contents differed by less than 15 mol percent, while blends where one or both E‐V copolymers are crystalline were found to be incompatible. The properties of these copolymers will be discussed in terms of their microstructure.

Analysis of PVC blends by three‐dimensional solubility parameters

“…Bowmer and Tonelli's study showed that the copolymer of vinyl chloride and ethyl acetate exhibited tremendous compatibility with PVC. 41 Although the method of 3-D solubility parameters is not suitable for the blends of PVC with any copolymer containing PVC as a constituent, one can still use eqs. (1) and (4)-(6) for various copolymers and calculate 8~ to predict the miscibility of such copolymers.…”