IN-SITU ANALYSIS OF SOLVENT NONSOLVENT EXCHANGE AND PHASE-SEPARATION PROCESSES DURING THE MEMBRANE FORMATION OF POLYLACTIDES/

Membrane formation of polylactides has been studied using in situ anal ysis techniques. An experimental method based on the use of dark groun d optics and reflected light illumination is used to monitor the mass transfer and phase separation dynamics during formation. Additionally, the phase separation and structure formation has been studied using o ptical microscopy. The results of the dark ground optics technique for the polymer/solvent/nonsolvent systems poly-L-lactide/chloroform/meth anol and poly-DL-lactide/chloroform/methanol showed that the diffusion kinetics were similar for the semicrystalline poly-L-lactide (PLLA) a nd the amorphous poly-DL-lactide, The influence of the molecular weigh t of the polymers on the diffusion kinetics was found to be negligible . Increasing the polymer concentration of the casting solution decreas ed the rate of diffusion. The phase separation of poly-DL-lactide was studied with optical microscopy and found to proceed via liquid-liquid demixing. For poly-L-lactide solutions of relatively low concentratio n (5-6% w/w), phase separation proceeded via liquid-liquid demixing fo llowed by crystallization. For more concentrated PLLA solutions, phase separation proceeded directly via solid-liquid demixing processes. Ad ditionally, for 6% w/w solutions of poly-L-lactide in dioxane immersed in methanol, precipitation also occurred solely via solid-liquid demi xing. (C) 1996 John Wiley & Sons, Inc.