Chemoenzymatic synthesis and chemical recycling of sustainable polyurethanes.

Two novel types of chemically recyclable ester-containing polyurethanes, namely, a diol-diacid-type poly(diester-urethane) (PDEU) and a hydroxy acid type poly(ester-urethane) (PEU), were prepared by a green synthetic route that avoids the use of hazardous diisocyanate. The urethane linkage was introduced by the reaction of ethylene carbonate with amino alcohols and amino acids to form urethanediol and urethane-containing hydroxy acids, respectively. The urethanediol underwent polymerization with dimethyl adipate in the presence of lipase to produce a high-molecular-weight PDEU, while PEU was prepared by the lipase-catalyzed direct polycondensation of the urethane-containing hydroxy acid monomer. The periodic introduction of ester linkages into the polyurethane chain afforded primary biodegradation points and chemically recyclable segments. Both PDEU and PEU were readily degraded in the presence of lipase into oligomers which were readily repolymerized in the presence of the same enzyme.