Synthesis and RAFT polymerisation of hydrophobic acrylamide monomers derived from plant oils†

Abstract

Polymeric materials based on fatty acids (FAs) have a combination of characteristics (alkene groups, hydrophobicity, tuneable T_g) that give them great potential as renewable, high value materials. Here, we investigate the base catalysed transesterification of four different plant oils (high oleic sunflower, olive, hydrogenated coconut and hydrogenated rapeseed) with N-hydroxyethyl acrylamide. By conducting kinetics experiments, investigating potential side reactions and improving isolation of the target products, we were able to identify reactive impurities (radical inhibitors, unintended co-monomers) that were found to remain in the impure brine washed plant oil-based monomers (POBM). Kinetics experiments were then performed to investigate the RAFT polymerisation of these monomers. It was found that the more sustainable brine washing process was viable for the controlled radical polymerisation of the higher k_{p app} (saturated) monomers, however column purification was necessary for good control of unsaturated monomers. Polymers with values of M_n between 3000 and 12 000 g mol⁻¹ were synthesised and dependent on the FA source exhibited either amorphous or semi-crystalline behaviour (T_g values between −1 and 33 °C, T_m values between 48 and 66 °C). This work demonstrates the first example of RAFT polymerisation of acrylamide monomers derived from plant oils by a one step direct transesterification, opening the door for novel well-defined, functional bio-based polymers.