Glycerol-, pentaerythritol- and trimethylolpropane-based polyurethanes and their cellulose carbonate composites prepared via the non-isocyanate route with catalytic carbon dioxide fixation

Abstract

Catalytic carbon dioxide fixation by carbonation of glycerol, trimethylolpropane and pentaerythritol glycidyl ether, followed by curing with citric acid amino amides in the presence of cellulose carbonate, represents an attractive green chemistry route to non-isocyanate polyurethanes (NIPU) and bio-based NIPU composites. In comparison to traditional polyurethanes, neither fossil resources nor toxic isocyanates are required. The glycidyl ethers react with carbon dioxide in the presence of tetrabutylammonium bromide catalyst to produce the cyclic carbonates of glycerol (GGC), pentaerythritol (PEC), and trimethylolpropane (TMC). The carbon dioxide fixation is 22.4 wt% for GGC, 29.5 wt% for PEC and 28.3 wt% for TMC. The preferred bio-based curing agent comprises a blend (CAA) containing hexamethylene diamine (HMDA) and citric acid amino amides, prepared by polycondensation of triethyl citrate with excess HMDA. According to the in situ ATR-FTIR-monitoring of urethane formation, the addition of 1,4-diazabicyclo[2.2.2]octan (DABCO) as the catalyst enables room temperature curing, whereas in the absence of DABCO 70 °C is required. In comparison to the very soft GGC resins, the GGC–PEC and GGC–TMC blends, cured with HMDA and CAA, improve simultaneously the glass transition temperature from 20 to 58 °C and Young's modulus from 7 to 2500 MPa, unparalleled by the individual blend components. The phosgene-free conversion of cellulose with diphenyl carbonate affords cellulose carbonate as a coreactive bio-based filler for the preparation of cellulose–NIPU composites with in situ urethane-mediated interfacial coupling.