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

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–Sx–(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 (Mw) increases, though not doubling as anticipated. In contrast, treating (PEP)2Zn synthesized using (CH2═CHC6H4CH2CH2CH2)2Zn (1) resulted in significant Mw 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 Mw multiblock copolymers (200–400 kDa), chain-extended with –Sx– linkages, from CCTP products such as (iPP-b-PEP)2Zn and (iPP-b-PE)2Zn. The resulting high-Mw polymers exhibited dramatically enhanced mechanical strength and viscosity showing pronounced shear thinning behavior compared to conventional acid-quenched CCTP products.