Synthesis of HDPE-b-iPP Diblock Copolymers via Subsequent Coordintive Chain-Transfer Polymerization and Their Use as Compatibilizers for HDPE/iPP Blends

An envisioned circular economy of commonly used polymers, high-density polyethylene (HDPE) and isotactic polypropylene (iPP), is challenging due to their immiscibility with almost all other plastics. Therefore, highly effective compatibilizers and synthetic protocols permitting their large-scale production are highly desirable. Herein, we report the efficient one-pot synthesis of strictly linear HDPE-b-iPP diblock copolymers achieved by coordinative chain transfer polymerization (CCTP). Various diblock copolymers with short and very narrow distributed HDPE (M n = 1400–2400 g × mol−1; Ð = 1.4) and long iPP segments were synthesized and used to compatibilize HDPE/iPP blends. The synthesized block copolymers differ in their overall molecular weights (M n = 10,600–60,600 g × mol−1) by varying the iPP segment, whereas the HDPE block was kept in a narrow range. Block copolymers with a molecular weight from M n = 23,000–39,000 g × mol−1 are competitive or outperform commercial compatibilizers, INFUSETM and INTUNETM, with the highest efficiency in compatibilizing 30/70 (wt./wt.) HDPE/iPP blends by a 5 wt.-% copolymer addition. SEM studies revealed that after adding the diblock copolymer, HDPE core shell structures were formed, and the HDPE particle size decreases compared to the neat blend, avoiding HDPE particles from debonding during tensile deformation tests.