Fast, catalyst-free room temperature production of isocyanate-free polyurethane foams using aromatic thiols†

Non-isocyanate polyurethane (NIPU) foams of the polyhydroxyurethane (PHU) type are promising greener alternatives to their conventional isocyanate-based polyurethane counterparts that dominate the foam market. Recently, concomitant organocatalyzed aminolysis and S-alkylation of the cyclic carbonates of PHU formulations offered a facile route to produce CO₂ self-blown PHU foams. However, this process was limited to the production of foams of rather low T_g (commonly up to room temperature) and suffered from slow foaming (i.e. 30 min) at 120 °C, thus still far from the foaming timeframes (1–10 min) and room temperature (r.t.) needed for adaptation to industrial foaming equipment. In this work, we elaborate strategies to accelerate thiol-assisted NIPU foaming in order for it to be complete in 5–10 minutes from r.t. reactive formulations under catalyst-free conditions. This is achieved by substituting aliphatic thiols by more acidic aromatic ones, and by adding epoxides as heat release promotors that will accelerate both the foaming and the curing rates. Moreover, flexible, semi-rigid and rigid foams are easily accessible by the choice of the amine comonomer and epoxide additive. This work draws general and simple concepts for greatly speeding-up the self-blowing NIPU process, a crucial step toward decreasing the energetic and production costs, offering potential for retrofitting existing foam production plants.