Polymerization-crosslinking of renewable itaconic acid in water and in deep eutectic solvents

Nowadays, the production of polymers from biomass-derived monomers is of large interest. It has the potential to decrease the dependence on non-renewable feedstocks and also could yield methods of synthesis of novel materials with unforeseen properties. We report here results of studies of copolymerization of renewable itaconic acid (IA) with N,N'-methylenebisacrylamide (MBA) in water, as well as in low melting mixtures based on choline chloride (deep eutectic solvent). Both, polymers formed in the pre-gelation period and also hydrogels produced in the post-gelation stage were investigated. H-1 NMR, DLS, SEC and elemental analysis indicated that the products isolated before gelation are branched copolymers with hydrodynamic size ranging from 10 to 100 nm and with average monomer composition of 7-9 mol% of MBA. The latter co-monomer was incorporated with 75-95% of unreacted (second) pendant vinyl groups, which can be later used for crosslinking. Post-gelation products (hydrogels) were characterized by gravimetric, DSC and compression-strain measurements. Swelling degree, amount of freezable water, shear moduli and effective crosslink density were determined. The mechanism of the polymeric network formation and its imperfect structure are discussed. It was also shown that polymerization in DES is faster than in water, and gelation occurs in a shorter time. In addition, hydrogels prepared in DES exhibit higher effective crosslink density and lower swelling degree.