Bifunctional Organophotocatalysis for Convenient, Efficient, and Controlled Synthesis of Hyperbranched Functional Polymers

Abstract

Combining polymerization-induced branching (PIB) with controlled radical polymerization (CRP) enables regulated and site-specific synthesis of hyperbranched polymers. However, it remains a challenge to apply this strategy to the synthesis of hydrophobic/oil-soluble hyperbranched polymers with important application value. Existing methods are either suitable for hydrophilic systems or suffer from crosslinking/low efficiency/low conversion in hydrophobic systems. Herein, amine-thiourea bifunctional organic catalysts, widely used in small-molecule asymmetric catalysis, are innovatively employed to construct photoinduced reversible complexation mediated polymerization (RCMP) system, realizing convenient, efficient and controlled synthesis of hydrophobic/oil-soluble hyperbranched polymers via one-shot copolymerization of acrylates and α-iodoacrylates. Monomer conversion reaches 98%, yielding hyperbranched polyacrylates with moderate dispersities (1.18–1.90) as well as tunable molecular weights (Mn = 40−190 kg/mol) and branching densities. In the bifunctional catalyst, the tertiary amine moiety complexes with the terminal iodine of the dormant species, inducing reversible cleavage of C–I bond to generate active radical species and enable subsequent controlled chain propagation. While the thiourea group anchors the catalyst through interaction with the terminal monomer unit, which is speculated to serve three functions: i) primarily suppressing biradical coupling/termination via shielding macromolecular radicals; ii) assisting in the activation of C–I bond in dormant species via reducing its electron density (bond energy) to promote chain propagation; iii) reducing the difference in reactivity ratios between inibramer and main monomer via hindering the radical addition of the highly reactive but sterically hindered α-iodoacrylate. Consequently, this bifunctional RCMP catalytic system avoids the slow rate, low conversion, severe inter-macromolecular coupling and even cross-linking issues in the ATRP and monofunctional RCMP catalytic systems, delivering fast polymerization and high conversion while suppressing cross-linking. The resulting polymer features a high retention degree of terminal functional groups and ease of modification, enabling its use as a high-performance multifunctional lubricant additive to facilitate the high-value utilization of reclaimed base oil, which holds great significance for environmental protection and resource conservation.