SINGLE-CRYSTALS OF SYNDIOTACTIC POLY[PROPENE-CO-(1-OCTENE)] AND SYNDIOTACTIC POLYPROPENE CRYSTALLIZED IN BULK

Single crystals grown in bulk samples of a syndiotactic random copolym er of propene and 1-octene with 4 wt.-% 1-octene are compared with sin gle crystals of syndiotactic polypropene homopolymer. The random copol ymer during isothermal crystallization at low supercoolings forms rect angular single crystals similar to syndiotactic polypropene. The singl e crystals of the random copolymer do not exhibit transverse cracks in contrast to neat syndiotactic polypropene. Both polymers have nearly the same linear thermal expansion coefficients along their crystallogr aphic a- and b-axis, calculated from temperature-dependent wide-angle X-ray scattering (WAXS) measurements. Therefore, the absence of transv erse cracks in single crystals of the random copolymer can only be exp lained by the relatively high disorder of the crystallite surface caus ed by the exclusion of 1-octene segments which leads to a more isotrop ic thermal expansion coefficient in this region.