Chemically crosslinked crystalline thermoplastic polyolefin elastomer with good elasticity and improved thermo-mechanical properties

Due to mechanical α-relaxation process, olefin block copolymer (OBC) has a limited heat resistance and thermo-mechanical property. In this work, peroxide-induced melt crosslinking was conducted to fabricate OBC elastomers with two types of crosslinks. It was found that orthogonal crystal structure forms in these chemically crosslinked elastomers. Interestingly, the crystallization peak temperature (T_c,p) shifted to higher temperature after crosslinking, which is mainly due to the crystallization mode transition from confined crystallization to breakout crystallization. Based on CPMG method of LF-¹H NMR and AFM nanomechanics, it was demonstrated that loosely crosslinked OBC achieves double crosslinks of one chemical crosslink and another well-interconnected crystalline crosslink. As a consequence, OBC elastomer with double crosslinks shows an obviously enhanced Young's modulus (∼13.5 MPa), improved high-temperature mechanical properties (∼2.2 MPa strength and ∼220% elongation at break @80 °C) and good damping property (tan δ = 0.42). Furthermore, a balanced reprocessability and elastic recovery can be reached by adjusting the quantity of chemical crosslinks. Therefore, our work can provide guidelines for structural design and related elasticity mechanisms for high performance thermoplastic polyolefin elastomer.