Sulfur Treatment of Coordinative Chain Transfer Polymerization Products for Extending Polyolefin Chains with Polysulfide Linkages

Abstract

Coordinative chain transfer polymerization (CCTP) is a state-of-the-art technology for producing olefin block copolymers. However, a key limitation of CCTP is its restricted molecular weight range achievable, as chain transfer reactions become inefficient when polyolefin chains attached to chain transfer agents exceed a certain length. This study presents a method for post-CCTP chain length extension, demonstrating that the reaction of CH₃(CH₂)₅Zn(CH₂)₅CH₃ with S₈ quantitatively produces CH₃(CH₂)₅–S_x–(CH₂)₅CH₃ (x = 1–5). Treating S₈ to ethylene/propylene CCTcoP products, i.e., (PEP)₂Zn, synthesized using Et₂Zn or (hexyl)₂Zn, led to molecular weight (M_w) increases, though not doubling as anticipated. In contrast, treating (PEP)₂Zn synthesized using (CH₂═CHC₆H₄CH₂CH₂CH₂)₂Zn (1) resulted in significant M_w increases by 2.8–3.8 times, attributed to additional chain extension through the reaction of styrene end groups with S₈. This approach enabled the synthesis of high M_w multiblock copolymers (200–400 kDa), chain-extended with –S_x– linkages, from CCTP products such as (iPP-b-PEP)₂Zn and (iPP-b-PE)₂Zn. The resulting high-M_w polymers exhibited dramatically enhanced mechanical strength and viscosity showing pronounced shear thinning behavior compared to conventional acid-quenched CCTP products.