Facile and Efficient In-Situ End-Functionalization of Neodymium-based Polybutadiene by Isocyanate Via a Coordinative Chain Transfer Polymerization Strategy

Tapping facile and efficient strategies for in-situ end-functionalization of polydiene elastomers has been pursued for scientists for decades. This has been especially prominent for Ziegler-Natta type catalytic systems, because they hold great potential for future large-scale industrializations. In this report, through using a newly emerged method of coordinative chain transfer polymerization (CCTP), we introduce a simple and convenient method to efficiently end-functionalize neodymium-based polybutadienes by in-situ addition of isocyanate or isothiocyanate compounds. These two types of substrates performed high reactivities with η1-allyl-Al capped polybutadienyl chain-ends, that were generated from fast and reversible chain transfer reactions, giving high functionalization efficiencies (up to 97.1%). The high functionalization efficiencies were also applicable to isocyanate or isothiocyanate substrates bearing different functionalities, showing a broad scope capability. Moreover, such a functionalization process was not influenced by the viscosities of the reaction system, as revealed from the kinetic studies that linear relationship was obtained between Mns and various [BD]/[Nd] ratios, implying again the high reactivities of the isocyanate or isothiocyanate compounds. Due to the incorporation of amide or thioamide functional group into the chain-ends, the corresponding polybutadienes showed much improved surface properties and performed higher mechanical properties than unfunctionalized counterparts for raw rubber matrix. Regarding the vulcanizate, chain-end functional groups could also result in much improved filler dispersion and stronger interaction between rubber and filler particles, which eventually gave rise to better mechanical properties, inducing higher tensile strength, more toughness, and greater tear strength.