Ethylene-propylene copolymerization initiated with solubilized ziegler-natta macromolecular complexes. II. Characterization of [styrene]-b-[ethylene-co-propylene] copolymers

Copolymerization of ethylene (E) with propylene (P) initiated with soluble (polystyrene)₁₀₀-butadiene₃-Li/TiCl₄ complexes leads to St]-b-E-co-P] diblock copolymers with a random E-P] block. GPC and ¹³C-NMR analyses of copolymers with various compositions and block lengths disclose well-defined linear structures. From DSC measurements of such materials, three different endothermal transition regions are observed: two glass transition regions corresponding, respectively, to the T_g of styrenic and olefinic blocks, and one E-P] block melting region in which propylene units play a primary role. Furthermore, an additional endotherm is observed, depending on the thermal history of the sample.