The structure of neoprene. VI. Crystallization

Abstract

Abstract A volume dialometric study of the crystallization behavior of polychloroprenes made at −40°, 10°, and 40°C. has shown that the melting point of the crystalline phase in these polymers is an inverse linear function of polymerization temperature. Polychloroprene made at −40°C. melts at ca. 65°C., while conventional 40°C. neoprenes melt at ca. 40°C. Comparison of this data with the melting point depression observed in a chloroprene/methacrylonitrile copolymer and in polychloroprene/diluent mixtures has made possible calculations which confirm earlier hypotheses that neoprenes have a highly regular structure. Commercial neoprenes made at 40°C. are calculated to consist of 80–85% of the trans ‐2‐chloro‐2‐butylene units which result from trans ‐1,4 polymerization of chloroprene. Densities determined for crystalline and amorphous neoprenes have been used to calculate the degree of crystallinity of these polymers, and this information has made possible calibration of the infrared crystallization‐sensitive bands, for use in measurement of degree of crystallinity. The heat of fusion of the crystalline phase of neoprenes has been found from diluent data to be 22.7 ± 2 calories per gram.