Thermodynamic parameters of poly(lactic acid) solutions in dialkyl phthalate

Some of thermodynamic parameters for poly(lactic acid) (PLA)/dialkyl phthalate systems have been investigated. Both poly(dl-lactic acid) (PDLLA) and poly(l-lactic acid) (PLLA), which are stereoisomers of PLA, were used and a series of 1,2-dialkyl phthalates with different alkyl chain, from methyl to hexyl, was adopted as a solvent. Theta temperatures of PLA/dialkyl phthalate system were determined and subsequently the second virial coefficient and the interaction parameter were evaluated. Theta temperature was determined by the extrapolation of the highest liquid–liquid phase separation temperatures and Zimm plots were constructed by static light scattering to obtain second virial coefficient and z-average radius of gyration. Second virial coefficient and z-average radius of gyration was examined quantitatively as a function of temperature and solvent. Thermodynamic parameters that could not be obtained experimentally were calculated based on the Flory–Huggins theory.