Synthesis of α,ω-end hetero-functionalized polyisoprene via neodymium-mediated coordinative chain transfer polymerization

Abstract

Tapping facile and efficient strategies for preparing α,ω-end hetero-functionalized polyisoprene (PIp) that mimics the chain structure of natural rubber (NR) has been a long-standing pursuit in polymer science. In this study, we present a novel approach utilizing neodymium-catalyzed coordinative chain transfer polymerization (CCTP) to construct end-functionalized PIps with distinct functional groups at the α- and ω-termini. The α-end functionalization was achieved by incorporating copolymerizable heteroatomic 1-substituted dienes (Bd_PhX) during the aging stage of polymerization. By varying the type and feed ratio of Bd_PhX, a diverse array of α-functional moieties with tunable incorporation levels was readily obtained. Detailed kinetic studies revealed that the presence of α-functional Bd_PhX moieties exerted minimal impact on the CCTP process, maintaining highly reactive allyl–metal bonds (predominantly allyl–Al bonds) crucial for subsequent ω-end functionalizations. The ω-end functionalization was realized through two complementary strategies: (1) the incorporation of copolymerizable diene derivatives and (2) in situ reactions with reactive small molecules. The first approach was achieved by introducing Bd_PhX monomers, while in the second approach, reactive small molecules such as isothiocyanates and oxygen, were employed to construct thioamide and hydroxyl end-functional groups, respectively. The synthesized polymers were comprehensively characterized to confirm their structures and functionalities, highlighting the versatility and efficiency of this strategy for designing α,ω-end hetero-functionalized PIps.