MICROPHASE SEPARATION IN POLY(OXYETHYLENE)-POLY(OXYBUTYLENE) DIBLOCK COPOLYMERS

Twenty-six poly(oxyethylene)-poly(oxybutylene) diblock copolymers were prepared by anionic polymerization. The phase behavior of these copol ymers was studied near the order-disorder transition over the composit ion range from 0.21 to 0.84 poly(oxyethylene) volume fraction. Small-a ngle X-ray scattering was used to characterize phase transition temper atures and ordered state symmetries. Four distinct microstructures wer e observed: body-centered cubic, hexagonally packed cylinders (hex), l amellae (lam), and a bicontinuous cubic phase with <Ia(3)over bar d> s ymmetry, together with a less well-defined region of the phase diagram comprising either hexagonally perforated layers or biphasic hex and l am. The Flory-Huggins parameter as a function of temperature was estim ated using both the mean-held approximation and a fluctuation correcti on to the mean-field theory. The experimental microphase behavior is c ompared with the exact mean-field phase diagram calculated using self- consistent-field theory.