Melting and crystallization behavior of binary blends of syndiotactic polypropylenes of different stereoregularity

Binary blends of samples of syndiotactic polypropylene of different stereoregularity have been prepared by mixing a more stereoregular and crystalline sample sPP1 having [rrrr] = 78%, with low stereoregular and poorly crystalline samples samPP1 and samPP2 having [rrrr] = 54.6 and 45.8%, respectively, and a nearly atactic fully amorphous sample amPP1 with [rrrr] = 26.5%. The blends show separate melting of the two components with the more stereoregular component sPP1 melting at high temperature and the poorly syndiotactic component melting at lower temperature. Crystals of sPP1 are formed by cooling from the melt whereas more defective crystals of samPP1 and samPP2 are formed by cold crystallization during aging at room temperature. The presence of the strereoirregular component disturbs the melt crystallization of the stereoregular component sPP1 and depression of the crystallization and melting temperatures of sPP1 in the blends is observed. On the other hand, the cold crystallization at room temperature of the irregular component is accelerated and favored by the presence of the more stereoregular component sPP1, whose crystals act as crystallization nuclei. All data indicate interactions between the components in the melt and amorphous state, compatible with a good degree of mixing.