Miscibility and Specific Interactions in Blends of Poly(<scp>l</scp>-Lactide) with Poly(Vinylphenol)

Abstract

This paper reports a DSC and FTIR study of blends of poly(l-lactide) (PLLA) with poly(vinylphenol) (PVPh). According to the single Tg criterion, miscibility has been found in all the compositions range for the blends obtained by solution/precipitation in a dioxane/hexane pair. However, phase separation has been observed for PVPh-rich blends obtained by solvent casting from dioxane solutions. The Tg of the blends shows negative deviation from linearity. Hydrogen bonding has been found, and the band attributed to hydrogen-bonded carbonyl groups is shifted about 18 cm-1, suggesting relatively weak hydroxyl−ester hydrogen bonds. The equilibrium melting points of pure PLLA and different blends have been recorded, and the values of the interaction parameter χ12 = −0.42 and the interaction energy density B = −8.8 cal/cm3 have been calculated. The negative value of the interaction parameter confirms a thermodynamically miscible blend. The value of B is similar to the value found in poly(ε-caprolactone) (PCL)/PVPh. This small difference between both systems is feasible because the weaker attractive interactions found in PLLA/PVPh counteract against weaker repulsive interactions, as the solubility parameter of PLLA (δ = 10.1 (cal/cm3)1/2) is closer to PVPh (δ = 10.6 (cal/cm3)1/2) than the solubility parameter of PCL (δ = 9.2 (cal/cm3)1/2).