Cationic Ring-Opening Polymerization of Optically Active N-Substituted Cyclic Thiourethanes

N-substituted cyclic thiourethanes [4( S )-(methoxycarbonyl)- N -benzyl-1,3-oxazolidine-2-thione ( BnS L ), 4( S )-(methoxycarbonyl)- N -benzoyl-1,3-oxazolidine-2-thione ( BzS L ), and 4( S )-(methoxycarbonyl)- N -acetyl-1,3-oxazolidine-2-thione ( AcS L )] were synthesized from l -serine methyl ester hydrochloride and were polymerized by using methyl trifluoromethanesulfonate to obtain the corresponding well-defined polythiourethanes. The molecular weight of the polymers can be controlled by the ratio of the monomers to the initiator and the molecular weight distributions are narrow ( M w / M n < 1.15) similar to the previously reported polymerization of a cyclic thiourethane [4( S )-(methoxycarbonyl)-1,3-oxazolidine-2-thione ( S L )]. The polymerization rates are on the order of S L > BnS L > BzS L > AcS L, which agrees well with the nucleophilicity of the thiocarbonyl moieties of the monomers ( S L, BnS L BzS L, and AcS L ). The Cotton effects in the CD spectra of the polymers from the N-substituted monomers exhibit almost inverse shape with that of poly( S L ) and the specific rotations' signs also inversed, suggesting the idea that poly( S L ) and N-substituted polymers take different high order structures.