Synthesis of high molecular weight poly(ricinoleic acid) via direct solution polycondensation in hydrophobic ionic liquids

Ricinoleic acid, a natural hydroxy fatty acid, is a good candidate for preparing biodegradable polymer elastomers. Herein, high molecular weight poly(ricinoleic acid) (PRA) with a weight average molecular weight up to 122 kDa was successfully synthesized by solution polycondensation of methyl ricinoleate (MR) in hydrophobic ionic liquids, 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide. The influence of monomer concentration, polymerization temperature and time, catalyst and properties of the ionic liquids on the polycondensation was comprehensively studied. Compared with the melt polycondensation, the solution polycondensation of MR in the ionic liquids can achieve much higher molecular weights. The PRA polymerized in ionic liquids shows a 100% cis structure like the natural monomer.