Order–disorder transition of starblock copolymers

Small-angle x-ray scattering from the segmental density fluctuations of a starblock copolymer with a given arm number n of 6 as well as that of a linear diblock copolymer (corresponding to the starblock copolymer with n=1) were studied in both ordered and disordered states. In the ordered state the characteristic wavelength (D) of the fluctuations for the copolymer with n=6 was found to have the same temperature (T) dependence as that for the diblock copolymer, where n=1, i.e., D∼T−1/3. In the disordered state, the theoretical spectrum of the fluctuations was found to essentially agree with the experimental results. The thermodynamic interaction parameter (χ) between the dissimilar monomers was also determined as a function of T from the fluctuation spectrum in the disordered state. The results show a significant n dependence.