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

Tapping facile and efficient strategies for preparing alpha,omega-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 alpha- and omega-termini. The alpha-end functionalization was achieved by incorporating copolymerizable heteroatomic 1-substituted dienes (BdPhX) during the aging stage of polymerization. By varying the type and feed ratio of BdPhX, a diverse array of alpha-functional moieties with tunable incorporation levels was readily obtained. Detailed kinetic studies revealed that the presence of alpha-functional BdPhX moieties exerted minimal impact on the CCTP process, maintaining highly reactive allyl-metal bonds (predominantly allyl-Al bonds) crucial for subsequent omega-end functionalizations. The omega-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 BdPhX 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 alpha,omega-end hetero-functionalized PIps.