Polymerization of 2,2-dimethyltrimethylene urethane; a disfavoured process

Abstract

The ring-opening polymerization of 2,2-dimethyltrimethylene urethane (DTU, 1) is a thermodynamically disfavoured process. According to calorimetric measurements by Lebedev et al., the Gibbs energy of polymerization in bulk varies between 29 kJ · mol−1 and 23 kJ · mol−1. Poly(DTU) (2) was synthesized by polycondensation of an activated dimeric hydroxyurethane (DDPP, 3) in an end group selective reaction. The selectivity of the polycondensation is influenced by temperature and the catalyst chosen, and best results were obtained at 120°C employing Bu2Sn(OOC(CH2)10CH3)2 as a catalyst, which favours end group reaction rather than intramolecular transurethanization. Poly(DTU) (2) was degraded at 120°C in a closed system to yield a mixture containing 94 wt.-% of DTU and 6 wt.-% of oligomers. The depolymerization proceeds via formation of cyclic oligomers as intermediates.