Effects of chain configuration on the crystallization behavior of polypropylene based copolymers

The effects of sequence distribution of two types of poly(propylene-ethylene) (PP-PE) copolymers, with propylene being the dominant component, on the associated crystallization behavior have been analyzed. The average sequence lengths of the crystallizable propylene sequences in these copolymers are different, although the ethylene content was virtually identical. In one case the chain configuration was completely random with crystallizable propylene sequences following Bernouillian statistics. In the other case, a bimodal distribution of crystallizable polypropylene sequences can be produced. The crystallization kinetics, the crystallization temperature, and the degree of crystallinity were significantly higher for the latter sample as compared to the former. When crystallizing from the melt, the longest crystallizable propylene sequences crystallized first at any supercooling, thus controlling the segmental mobility of other segments in the distribution. This is especially evident in copolymers with the bimodal segmental distribution. The distribution of crystallizable polypropylene sequences also controls the size distribution and thermal stability of the crystallites formed. The elucidation of the crystallization behavior of these copolymers is crucial in defining the application driven setting speeds of hot melt adhesives, the principal application of interest in our laboratory. (C) 2017 Elsevier Ltd. All rights reserved.