Polystyrene Chain Growth Initiated from Dialkylzinc for Synthesis of Polyolefin-Polystyrene Block Copolymers

Polyolefins (POs) are the most abundant polymers. However, synthesis of PO-based block copolymers has only rarely been achieved. We aimed to synthesize various PO-based block copolymers by coordinative chain transfer polymerization (CCTP) followed by anionic polymerization in one-pot via conversion of the CCTP product (polyolefinyl)₂Zn to polyolefinyl-Li. The addition of 2 equiv t-BuLi to (1-octyl)₂Zn (a model compound of (polyolefinyl)₂Zn) and selective removal or decomposition of (tBu)₂Zn by evacuation or heating at 130 °C afforded 1-octyl-Li. Attempts to convert (polyolefinyl)₂Zn to polyolefinyl-Li were unsuccessful. However, polystyrene (PS) chains were efficiently grown from (polyolefinyl)₂Zn; the addition of styrene monomers after treatment with t-BuLi and pentamethyldiethylenetriamine (PMDTA) in the presence of residual olefin monomers afforded PO-block-PSs. Organolithium species that might be generated in the pot of t-BuLi, PMDTA, and olefin monomers, i.e., [Me₂NCH₂CH₂N(Me)CH₂CH₂N(Me)CH₂Li, Me₂NCH₂CH₂N(Me)Li·(PMDTA), pentylallyl-Li⋅(PMDTA)], as well as PhLi⋅(PMDTA), were screened as initiators to grow PS chains from (1-hexyl)₂Zn, as well as from (polyolefinyl)₂Zn. Pentylallyl-Li⋅(PMDTA) was the best initiator. The M_n values increased substantially after the styrene polymerization with some generation of homo-PSs (27-29%). The M_n values of the extracted homo-PS suggested that PS chains were grown mainly from polyolefinyl groups in [(polyolefinyl)₂(pentylallyl)Zn]^-[Li⋅(PMDTA)]⁺ formed by pentylallyl-Li⋅(PMDTA) acting onto (polyolefinyl)₂Zn.