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 copolymer of propene and 1-octene with 4 wt.-% 1-octene are compared with single crystals of syndiotactic polypropene homopolymer. The random copolymer during isothermal crystallization at low supercoolings forms rectangular single crystals similar to syndiotactic polypropene. The single 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 crystallographic a- and b-axis, calculated from temperature-dependent wide-angle X-ray scattering (WAXS) measurements. Therefore, the absence of transverse cracks in single crystals of the random copolymer can only be explained by the relatively high disorder of the crystallite surface caused by the exclusion of 1-octene segments which leads to a more isotropic thermal expansion coefficient in this region.