Crystallization and Mechanical Properties of Butadiene-Derived Polyolefin Triblock Copolymers

Block copolymers containing poly(ethylene) (E) and poly(ethylene-stat-butylene) (X) blocks exhibit physical properties governed by microphase-separated semicrystalline E and amorphous X blocks. Previous studies focused on EX diblocks, leaving the influence of molecular architecture on phase behavior largely unexplored. This study investigated the phase behavior and mechanical properties of EXE triblocks with increasing butylene unit fractions in the E block (x), corresponding to decreasing crystallinity. Thermal and morphological characterization revealed that the E blocks crystallized within the microphase-separated lamellar domains with nearly identical crystallization behavior as the E homopolymers. These observations are attributed to the high molecular weight of the E block, forming large domains that do not appreciably confine crystallization. A crystallinity-dependent plastic-elastomeric transition occurred with increasing x, where the strain at break increased from approximately 800% to over 2200%. These findings provide valuable insights into crystallizable block copolymers and highlight EXE as a promising material with widely tunable properties.