Feasibility of polyamines and cyclic carbonate terminated prepolymers in polyurethane/polyhydroxyurethane synthesis

Abstract

Polyurethanes are a well-established part of adhesive markets. However due to the toxicity of di-isocyanates used in the synthesis, finding an alternative route to synthetize polyurethanes is increasingly important. One strategy is to use cyclic carbonate terminated prepolymers with polyamines to yield polyhydroxyurethanes. This research highlights the possibility to use commercially available polyurethane prepolymers with different isocyanate chemistries for cyclic carbonate terminated prepolymer synthesis with the help of glycerol carbonate and a catalyst. These synthetized prepolymers were used in a screening study with different commercially available low toxic amines. It was observed that when secondary amines were used, the reaction advanced at room temperature with no further heating required. The development of lap shear strength over time on stainless steel, gel content, tensile strength and elongation were measured from room temperature cured polymers. The synthetized polyurethane/polyhydroxyurethane (PU/PHU) hybrid materials had high initial lap shear strength close to current industrial polyurethane adhesives. The strength development over time was negligible. Full conversions were seen within one month from the reaction. Tensile strength levels were slightly lower than typical industrial polyurethane adhesives. Even though the lap shear strength results and gel contents at room temperature were on a good level, curing at elevated temperature had a positive impact on them. The best performing combination was cyclic carbonate functionalised hexamethylene di-isocyanate prepolymer with multifunctional polyethyleneimine amine. In short, di-isocyanate free PU/PHU hybrid materials were successfully synthetized from commercial raw materials and their performance was comparable with current industrial polyurethane adhesives.