Polydispersity effects on the phase diagram of the system chloroform/poly-L-(lactic acid)/poly(methyl methacrylate) and morphology of PLA/PMMA films

Cloud point curve, critical composition and several critical coexistence cu rves were measured at 25 degrees C for the ternary system poly-L-(lactic ac id) (PLA), poly(methyl methacrylate) (PMMA) - where both polymers exhibit b road molecular weight distributions - and the common solvent chloroform; In contrast to the situation encountered in the absence of the second polymer both branches of the critical coexistence curves are located without any d oubt inside the miscibility gap as defined by the cloud point curve. This u nexpected experimental finding is corroborated by model calculations on the basis of continuous thermodynamics. The removal of solvent from the ternar y mixtures yields films of different morphology, depending on the particula r path through the metastable or unstable regions of the phase diagram. The structures observed by means of optical microscopy confirm the theoretical ly postulated phase separation mechanisms. (C) 2000 Elsevier Science B.V. A ll rights reserved.