Molecular design alterations within systems containing poly(lactic acid)

Date of Completion

January 1998


Chemistry, Polymer|Textile Technology




The preparation of multiphasic polymer systems based upon poly(lactic acid)(PLA) has been undertaken to determine the effects of phase size and hydrophobic content upon mechanical response and hydrolytic stability. First, to clearly illustrate these basic principles, it was shown that block copolymers of poly($\varepsilon$-caprolactone)(PCL) and poly(1-lactide)(PLLA) could be synthesized with predictable glass and melt transition temperatures, respective domain size and dynamic mechanical properties. These properties were dictated according to the amount and length of PCL-diol serving as macroinitiator for the ring-opening polymerization of 1-lactide monomer.^ With the thought of attaining similar research goals and an eye toward socioeconomic concerns, reactive melt blends of highly amorphous PLA and oligo(hexamethylene succinate)(PHS) were produced to delineate the effects of a concentration limit of oligoester as micro- and macrophase separation develops. As PHS approached 20 weight percent, DSC analysis suggested the initial stages of growth of a PHS phase separate from the PLA semi-crystalline character. This finding was integral in the decision to incorporate oligo-$\varepsilon$-caprolactones(o-CL) as additives within larger-sized PCL/PLA blends in an effort to fully complement the attributes of the respective polyesters, while limiting the economic and environmental pressures imposed through the variables of time and organic solvent use.^ As the fundamental concepts of miscibility in relation to average molecular size, concentration and constituent interaction were established, the final portion of the work was dedicated to the coordination of mechanical response with a material's ability to withstand degradative conditions. It was concluded that rates of hydrolysis, in reference to PLA, were slowed by a combination of phase morphology and hydrophobicity incurred by the complementary components. These structural factors may have also played a role in the observed microbial specificity. ^