Thermally Induced Phase Transitions in Amorphous-Crystalline Brush Block Copolymers

Temperature resolved small angle x-ray scattering (SAXS) and wide-angle x-ray scattering (WAXS) were used to investigate the temperature dependent phase transitions of five lamellae forming poly(styrene)-block-poly(ethylene oxide) (PS-b-PEO) brush block copolymers. Asymmetric lamellar morphologies were observed for all the PS-b-PEO series irrespective of their volume fraction and backbone length. The temperature dependent SAXS and WAXS reveal the presence of long-range order up to 140 °C. Unlike their linear counterparts, the primary peak position (q*) and full-width half maximum (FWHM) of q* remain constant, indicaxting no order-disorder transition (ODT) up to 200 ° C. The melting and crystallization of the PEO side chains co-exists within the lamellar morphology. Isothermal crystallization studies were conducted to investigate the crystallization kinetics of the PEO domain. The results indicate a two-stage crystallization process with Avrami exponents of 1 and 2, suggesting a one-dimensional initial stage followed by two-dimensional growth at later times.