BLENDS OF AMORPHOUS-CRYSTALLINE BLOCK-COPOLYMERS WITH AMORPHOUS HOMOPOLYMERS .2. SYNTHESIS AND CHARACTERIZATION OF POLY(ETHYLENE-PROPYLENE)DIBLOCK COPOLYMER AND CRYSTALLIZATION KINETICS FOR THE BLEND WITH ATACTIC POLYPROPYLENE

A symmetric diblock ethylene-propylene copolymer (DEP) was synthesized through hydrogenation of an anionically polymerized polybutadiene-pol y(2-methyl-1,3-pentadiene) diblock copolymer (PBD-b-PMPD). IR and NMR measurements showed the hydrogenation to be more than 98 % complete. T he resultant diblock copolymer consists of an atactic polypropylene bl ock and a polyethylene block (b-PE) containing 3 mol % of ethyl branch es. Differential scanning calorimetry (DSC) was carried out for three series of binary blends made from DEP (M(w) = 113 x 10(3)) and three a tactic polypropylene (APP) samples with molecular weights of M(w) = 15 , 39, and 190 x 10(3). Blending did not affect the melting behavior of b-PE but drastically altered the crystallization behavior depending o n the molecular weight and composition of the blend. Adding APP to DEP caused the primary crystallization peak to shift to lower temperature . In the composition range of more than 50 wt % of APP, another new cr ystallization peak appeared around 70 degrees C for all blends. This f eature was especially pronounced for the blends with the lowest molecu lar weight APP. Isothermal crystallization studies were carried out fo r the blends and the data were analyzed by the Avrami theory. The anal ysis indicates that the dimensionality of the crystallization growth g eometry was reduced by blending and each crystallization peak could be correlated with a different dimensionality in the growth geometry. Th ese results are consistent with the framework of the currently accepte d microphase separation model for homopolymer/diblock copolymer blends .