Controlled RAFT synthesis of side-chain oleic acid containing polymers and their post-polymerization functionalization

Abstract

This study provides new insights into the design and controlled synthesis of side-chain unsaturated fatty acid containing polymers, with specific attention to facile post-polymerization modification reactions. The methacrylate derivative of oleic acid, 2-(methacryloyloxy)ethyl oleate (MAEO), has been synthesized and polymerized by the reversible addition-fragmentation chain transfer (RAFT) process to obtain poly(2-(methacryloyloxy)ethyl oleate) (PMAEO) with controlled molecular weight, narrow molecular weight distribution (Đ) and known chain ends. The PMAEO is capable of subsequent chain extension to form well-defined block copolymers via the RAFT technique. Double bonds in the oleate side-chains in PMAEO are further reacted with various organic thiol compounds via thiol-ene based thia-Michael addition reactions in the presence of 2,2′-azobisisobutyronitrile (AIBN) as radical source at 60 °C in tetrahydrofuran (THF) solvent. ¹H NMR spectroscopy indicated quantitative conversion of double bonds with ethanethiol, butanethiol, dodecanethiol and 3-mercaptopropanoic acid, whereas 2-mercaptoethanol gave ∼90% thioether product. The side-chain double bonds of PMAEO were quantitatively epoxidized using meta-chloroperbenzoic acid (mCPBA) at room temperature in dichloromethane, which was further cross-linked by 1,3-diaminopropane. Therefore, side-chain oleate pendants are ideal for various post-polymerization modifications to prepare renewable resource derived controlled macromolecular architectures with potential practical applications in fields such as paints, adhesives, electrical insulators, thermoplastics, etc.