POLYMERIZATION OF (3S,6S)-3-ISOPROPYL-6-METHYL-2,5-MORPHOLINEDIONE WITH TIN OCTOATE AND TIN ACETYLACETONATE

Polymerization of (3S,6S)-3-isopropyl-6-methyl-2,5-morpholinedione (1) with tin octoate (Sn(oct)(2)) and tin acetylacetonate (Sn(acac)(2)) r esults in an alternating polymer with lactic acid and valine repeating units, poly[(S)Lac-alt-(S)Val] (2). From time dependent analysis of t he monomer conversion and the number average molecular weight of the p olymer it is concluded that Sn(oct)2 acts as a catalyst and Sn(acac)(2 ) as an initiator. From H-1 NMR spectroscopic analysis of the polymer 2 it is concluded that the lactate moiety suffers from racemization du ring polymerization, while the valine moiety does not. The number rati o of not racemized repeating units (S,S) and racemized repeating units (R,S) in the polymer was calculated to be 11.5 for the polymer prepar ed with Sn(oct)(2) as a catalyst and 18.9 for the polymer prepared wit h Sn(acac)(2) as an initiator.