Microphase separation in amorphous poly(imide siloxane) segmented copolymers

A series of amorphous poly(imide siloxane) (PIS) segmented copolymers with various segmental lengths and contents of poly(dimethyl siloxane) (PDMS) were synthesized by condensation polymerization. Extraction was utilized to obtain highly pure PISs for a study of phase separation. The PISs self-assemble from dilute solutions that are initially rod-like structures and then rapidly transform to vesicles. Moreover, the vesicles change to solid spheres as the PDMS content increases. A variety of morphologies of the PIS films, including unilamellar vesicle, multilamellar vesicle, sea-island and others, are found as a function of the content and the segmental length of PDMS. Small angle X-ray scattering demonstrates the coexistence of large-scale phase separations and nano-scale phase separations of approximately 20 nm. The DSC results reveal that the phase separation is induced and dominated by the aggregation of PDMS segments. Furthermore, the surfaces of the hard phases in the PDMS-900 PISs are found to be fractal.