Macromolecules, Vol.49, No.18, 6817-6825, 2016
Base-to-Base Organocatalytic Approach for One-Pot Construction of Poly(ethylene oxide)-Based Macromolecular Structures
A base-to-base organocatalytic approach has been developed for one-pot synthesis of poly(ethylene oxide)-block-polyesters and poly(ethylene oxide)-based polyurethanes. Ethylene oxide is first polymerized from a diol in the presence of a phosphazene superbase; then a thiourea is added to be deprotonated by the strongly basic alkoxide, which attenuates the basicity of the catalytic system and thus allows for controlled polymerization of the subsequently added cyclic ester from the polyether chain end or for step-growth polymerization of an added diisocyanate with the macrodiol which is free from anionic homopolymerization of the diisocyanate. The approach shows several advantages in addition to the one-pot facile character, e.g., a wide applicability toward different "second monmers" including (but not limited to) epsilon-caprolactone, l-lactide, and diisocyanate, and a low amount of "second catalyst" required as the deprotonated thiourea itself serves as the mildly or weakly basic organocatalyst. Impact of the N-substituent, i.e., pK(a) of the thiourea, on the catalytic efficacy of the deprotonated thiourea has also been preliminarily revealed.