The aza-Michael reaction: towards semi-crystalline polymers from renewable itaconic acid and diamines

Abstract

This study reports, for the first time, semi-crystalline polymers based on bis-pyrrolidone dicarboxylic acids (BPDA) derived from renewable itaconic acid and various diamines. Rigid BPDA monomers could be obtained in high purity and yield from dimethyl itaconate, instead of the normally used itaconic acid as the starting material. The reduction in the melting point of dimethyl-BPDA monomers, compared to that of normal BPDA monomers, enables melt-polycondensation thus avoiding the need for a solvent in the oligomerization step. Under standard polycondensation conditions, the dimethyl-BPDA monomer with a rigid trans-cyclohexanediamine (t-CH-BPDA) could readily be polymerized with linear aliphatic diols (C₆ to C₁₂) to yield high molecular weight polyesters. These polyesters are the first in their class to be reported semi-crystalline, having a T_g between 65 and 33 °C and a T_m between 213 and 184 °C, with an increasing aliphatic chain length. Furthermore, even in the presence of hydrophilic pyrrolidone groups, semi-crystalline polyesters based on t-CH-BPDA showed high stability in water with no significant water uptake. Preliminary studies show that t-CH-BPDA monomers can also be polymerized into semi-crystalline polyamides, although insolubility and an unstable melt prevented the accurate characterization of the synthesized polyamides. Though trans-cyclohexanediamine is currently not available from biomass, the potential biomass content in the described semi-crystalline polyesters ranges from 71% for the C₆ diol up to 81% for the C₁₂ diol.