Determination of Sharpness of Order-Disorder Transition of Block Copolymers by Scattering Methods

It has been considered that elastic scattering profiles gradually change with temperature across the order-disorder transition (ODT) of block copolymers and hence a unique determination of the ODT temperature ( T ODT ) is difficult by scattering methods alone. We report here our finding that the scattering experiments with a high temperature-resolution, involving a temperature increment of smaller than or equal to 1°C, enables a straightforward, unequivocal determination of T ODT even for a low molecular weight polystyrene- block -polyisoprene copolymer. Moreover we found that the high temperature-resolution scattering experiment can reveal the very sharp ODT of the copolymer occurring in a very narrow temperature range of less than 1° C; the experimental results with a low temperature-resolution can easily lead us to overlook the sharpness of the ODT and to misunderstand the nature of the transition.