Synthesis of High Molecular Weight Isocyanate‐Free Polyurethanes by Transurethanization of Dimethyl Carbamate With Mixtures of Long and Short Chain Diols

Due to sustainability challenges associated with conventional polyurethanes (PUs), non-isocyanate polyurethanes (NIPUs) synthesized via transurethanization of bismethylcarbamates and diols provide a more environmentally friendly alternative for thermoplastic PU production. In this study, NIPUs were synthesized by transurethanization of dimethyl dodecane-1,12-diyldicarbamate with one polyol dihydroxy-telechelic poly(ethylene glycol) and two short-chain diols (1,5-pentanediol and 1,12-dodecanediol). The reaction was optimized using dihydroxy-telechelic poly(ethylene glycol) as a model diol, where the choice of KOtBu as a catalyst, a controlled alcohol/carbamate ratio (0.9) and mechanical stirring, enabled the production of high-molar-mass NIPUs (Mn up to 95 kg × mol$^{−1}$) at a relatively low temperature (120°C). Additionally, stepwise temperature adjustments (135°C and 150°C) were carried out to enhance polymerization efficiency, yielding NIPUs with improved molar masses. This method promotes the synthesis of NIPUs in a short time (∼6 h), using milder temperatures and three different diols. Further polymerization with different renewable diols led to NIPUs with tunable thermal properties, as assessed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), exhibiting relatively suitable thermal stability and semi-crystalline behavior associated with TPUs.