The compatibility between olefin block copolymers (OBC1 and OBC2) and isotactic polypropylene (iPP) was studied in this work.The two OBCs have similar hard block content and octene content

but are different in molecular weight.The linear viscoelasticity of OBCs were systematically studied.It was found from linear viscoelasticity that OBC1 with high molecular weight tends to exhibit strong mesophase separation

while OBC2 with low molecular weight is homogeneous in the studied temperature range.The interfacial tensions between OBCs and iPP were measured by drop retraction and dynamic rheological method.Both methods have achieved consistent results for the interfacial tension of the blends.The interfacial tension between iPP/OBC1 is around 1.17 mN/m

which is larger than that between iPP/OBC2 (about 0.3 mN/m).The variation of glass transition temperature in iPP/OBC blends were also studied by dynamic mechanical analysis

and depressions in the glass transition temperature of iPP were observed in both blends

from which the solubility of OBCs in iPP was estimated by self-concentration model.It was found that although the interfacial tension between OBC1 and iPP is larger

their miscibility is better.This is ascribed to the strong mesophase separation of OBC1.Further study on the crystallization of iPP in blends also justified the miscibility difference between iPP and the two OBCs.