Non-isocyanate thermoplastic polyureas (NIPUreas) through a methyl carbamate metathesis polymerization

Non-isocyanate thermoplastic polyureas (NIPUreas) were synthesized using an original approach. Dimethyl dicarbamates (DC) were prepared as monomers, by the reaction of a diamine with an excess of dimethylcarbonate (DMC), in presence of 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as catalyst. Then, self-polymerization of DC was performed through a methylcarbamate metathesis reaction, in presence of K2CO3 or TBD as catalysts. The reaction was conducted under neat conditions at 160 or 200 degrees C. NIPUrea analogues were also synthesized by melt transurethane polycondensation between DC and corresponding diamine, in presence of K2CO3 or TBD as catalyst at 160 degrees C. The thermal properties were dramatically dependent on the synthesis approach and operating conditions. The obtained NIPUreas displayed Tg values varying from 37 to 118 degrees C, T-m values varying from 95 to 289 degrees C, and thermal stabilities above 200 degrees C. The metathesis reaction with TBD has been found not effective. Using K2CO3 as catalyst, metathesis seems to afford higher molecular weight comparing to transurethanization.