Preparation of Sodium-Capped Poly(lactic acid) Oligomers by Catalytic Initiation with a Sodium α-, β-, or γ-Hydroxyacids

Abstract

Lactic acid oligomers were prepared using sodium and potassium hydroxyacids as initiators for lactide polymerization leading to the formation of surface active molecules in a one-pot synthesis, requiring no additional catalysts or volatile organic solvents. The initiator systems that were investigated included sodium and potassium salts of lactate, mandelate, γ-hydroxybutyrate, α-hydroxybutanoate, α-hydroxyhexanoate, α-hydroxyoctanoate, α-hydroxyisovalerate, and 2,2-bis(hydroxymethyl)butyrate. Poly(lactic acid) oligomers were successfully isolated from polymerizations initiated by all species listed using the catalyst-free synthetic route employed. The molecular weights of the oligomeric species ranged from 800 to 2400 Da (measured against poly(styrene) standards), and polydispersities were all below 1.5. All isolated polymers showed surfactant activity with low CMC values and a high propensity for aggregation that increases as molecular weight increases. Additionally, producing an A−B−A type polymeric structure, where the B block is defined as a moiety containing a single functional group, was shown to give improved application performance compared with the equivalent A−B type structure.