Synthesis of stereoregular cyclic poly(lactide)s via 'thiol-Ene' click chemistry

摘要

An experiment was conducted to demonstrate the application of thiol-ene click chemistry, specifically the Michael addition of thiols to maleimides, to synthesize and functionalize cyclic poly-(lactide)s. R,ω-maleimido- functional poly-(lactide)s were prepared by initiation of post-polymerization quenching of the aluminum-catalyzed ROP of lactide. Cyclization of the telechelic PLAs by concurrent slow addition of a precisely measured dichloromethane solution of the telechelic maleimide-functional PLA and an equal molarity dichloromethane stock solution of 1,2-thanedithiol to a stirred solution of triethylamine in dichloromethane that was saturated with sodium metabisulfite in order to suppress thiol reduction, at ambient temperature, provided mild conditions for the cyclization of PLA under pseudo-high-dilution conditions. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDITOFMS), 1HNMR, and gel-permeation chromatography (GPC) analysis of the resultant polymers unambiguously show that the cyclization has occurred in an efficient manner.