Organophosphate-catalyzed bulk ring-opening polymerization as an environmentally benign route leading to block copolyesters, end-functionalized polyesters, and polyester-based polyurethane†
The ring-opening polymerizations (ROPs) of ε-caprolactone (ε-CL), δ-valerolactone, 1,5-dioxepan-2-one, trimethylene carbonate, and L-lactide were performed in the bulk using an organophosphate, such as diphenyl phosphate, bis(4-nitrophenyl)phosphate, and di(2,6-xylyl)phosphate, as the catalyst. The ROPs proceeded in a well-controlled manner even under the bulk conditions to afford well-defined aliphatic polyesters, polyester–ether, and polycarbonate with relatively low dispersities. Notably, the amount of the loaded catalyst was successfully reduced when compared to the conventional organophosphate-catalyzed ROP in solution. A kinetic study revealed the controlled/living nature of the present bulk ROP system, which allowed us to produce the block copolymers composed of polyesters, polyester–ether, and polycarbonate in one pot. Syntheses of the end-functionalized poly(ε-caprolactone)s (PCLs) and poly(trimethylene carbonate) were successfully demonstrated using alcohol initiators possessing highly reactive functional groups. Furthermore, the α,ω-dihydroxy telechelic PCL-diol as well as the three- and four-armed star-shaped PCL-polyols were also easily obtained by using the polyols as an initiator. Finally, the one-pot synthesis of polyurethane via the ROP of ε-CL and a subsequent urethane forming reaction was demonstrated by taking advantage of the dual catalytic abilities of the organophosphate for both the ROP and polyurethane synthesis.