Stereocomplexation between PLA-like substituted oligomers and the influence on the hydrolytic degradation

Stereocomplex formation was revealed between two PLA-like oligoester enantiomers. Two oligomeric enantiomers of each α-hydroxyisovaleric acid and lactic acid were synthesized and two part blends were prepared between all oligomer combinations. The blends were evaluated by DSC and XRD and a new crystal structure was detected in the case of d/l oligo-α-hydroxyisovaleric acid blend confirming stereocomplexation. Stereocomplexation was also verified for the D/L oligolactic acid blend. The two stereocomplexes had higher melting temperatures and increased enthalpy of melting compared to the pure oligomers. Hetero-stereocomplexation between different enantiomers of oligo(α-hydroxyisovaleric) acid and oligo(lactic acid) did not take place. The hydrolytic degradation rate was slower for the blends containing the more bulky and hydrophobic oligo(α-hydroxyisovaleric acid)s. Modifying PLA with this monomer could be used to reduce the degradation rate and at the same time modify the physical properties of PLA materials.