Thermal behaviour and glass transition dynamics of inclusion complexes of alpha-cyclodextrin with poly(D,L-lactic acid)

Abstract

Inclusion complexes (ICs) have been prepared by the host-guest interaction between a-cyclodextrin (alpha CD) and poly(D,L-lactic acid) (PDLLA). This enables transformation of the amorphous polymer into a well organized channel-type crystalline structure, as studied by wide angle X-ray scattering (WAXS). WAXS experiments using synchrotron radiation allowed the evolution of this crystalline structure to be followed upon heating. The diffraction peaks disappeared above 320 degrees C, in a temperature region similar to the occurrence of thermal degradation, also investigated by thermogravimetric I analysis. No glass transition could be detected in the IC using differential scanning calorimetry (DSC), but non-conventional dynamic mechanical analysis measurements revealed the existence of loss factor peaks shifted to higher temperatures when compared with PDLLA. The relaxation plot of the IC was characterized by an Arrhenius behaviour with a high activation energy that could be consistent with the high geometrical confinement felt by the chains in the nanostructured organization.