Polylactones 27. Anionic polymerization of L‐lactide. Variation of endgroups and synthesis of block copolymers with poly(ethylene oxide)

Abstract

AbstractL‐Lactide was polymerized in toluene with various alkoxide initiators. These initiators were prepared in situ from potassium t.‐butoxide and primary or secondary alcohols such as tetradecanol, diethylene glycol butyl ether, menthol or testosteron. All these alcohols were incorporated as ester endgroups into the polylactide chain. However 1H‐NMR spectroscopy proves the existence of more OH‐endgroup than ester endgroups. This finding and 10–20% racemization observed for all anionic polymerizations suggest that chain‐transfer reactions with the monomer via deprotonation take place. When poly(ethylene glycol) monomethyl ether in combination with KOtBu was used as initiator, twoblock copolymers were obtained. With poly(ethylene glycol) A‐B‐A‐triblock copolymers could be synthesized. The quantitative reaction of the poly(ethylene glycol)s with L‐lactide could be proven by both 1H NMR spectroscopy and gelpermeation chromatography. DSC‐measurements show that depending on their lengths either the polylactide or the poly(ethylene oxide)blocks can crystallize. Due to partial racemization the melting temperatures (Tm) of the poly(L‐lactide) blocks did not exceed 155°C.