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Critical Value and Control of Complexation of Polylactide Blends Using Optical Purity

On the basis of the stereocomplex formation between poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA), the stereocomplexation-induced surface properties of enantimeric polylactide blends were inverstigated by electron spectrometer for chemical analysis (ESCA) and contact angle measurements as a function of a degree of complexation. The complexation of blends was controlled by using the stereochemical polylactides (stPLAs) with percent D repeat unit contents (optical purity) of 100, 98, 95, 90, and 85%. The PLLA-b-poly(dimethyl siloxane) (PDMS)-b-PLLA triblock copolymer, instead of PLLA was used as a surface probe material because of the high surface segregation of PDMS blocks. From ESCA measurements, the surface segregation of PDMS of PLLA-b-PDMS-b-PLLA/stPLA blends with ≤10% optical impurity was rapidly decreased with a degree of complexation. However, the uncomplexed blends >10% optical impurity showed that the surface segregation of PDMS was nearly that of PLLA-b-PDMS-b-PLLA. Similar behaviors were observed in the contact angle measurements. These results indicate that 10% optical impurity is a critical value at which the complex formation and the surface properties of the PLLA-b-PDMS-b-PLLA/stPLA blends can be controlled.