Synthesis of stereoregular poly(alkyl malolactonates)

Abstract

Optically pure methyl, ethyl, isopropyl, and benzyl (R)‐malolactonate were prepared from (S)‐(‐)‐malic acid and were polymerized in the bulk with tetraethylammonium benzoate as the initiator to yield high‐molecular‐weight, crystalline polymers. The optical purity of methyl and benzyl malolactonate was determined by ¹H NMR spectroscopy of the β‐lactone complexed with a chiral europium shift reagent. Enantiomeric excesses of 100% were found (the experimental error was 3%). Optically active poly(β‐malic acid) was obtained from optically active poly[benzyl (S)‐malate] by catalytic hydrogenolysis of the pendent benzyl esters. Ethyl and benzyl (R)‐malolactonate were also copolymerized, and the benzyl esters of the resulting copolymer were converted into carboxylic acid units by hydrogenolysis.