Morphological difference between solution-cast and melt-quenched crystalline-amorphous diblock copolymers

The morphology formed in poly(epsilon -caprolactone)-block-polybutadiene (P CL-b-PB) copolymers by casting the toluene solution was investigated by sma ll-angle X-Ray scattering (SAXS) and differential scanning calorimetry (DSC ) as a function of total molecular weight M-n and crystallization temperatu re T-c, and compared with the morphology formed by quenching from the micro phase-separated melt. The lamellar morphology was observed at any T-c in th e solution-cast PCL-b-PB with lower M-n (M(n)less than or equal to 30000), and the repeating distance of this morphology was little affected by T-c wh ile it increased significantly with increasing T-c for the quenched PCL-b-P B. The solution-cast PCL-b-PB with higher M-n (M(n)greater than or equal to 44000) had the lamellar morphology or crystallized microdomain structure ( i.e., a microdomain structure in which the PCL block partially crystallized ) depending on T-c though the crystallized microdomain structure was always observed in the quenched samples. The PCL crystallinity chi (c) (i.e., the weight fraction of crystallized PCL blocks against total PCL blocks in the system) was 0.63-0.79 in the lamellar morphology while it was considerably low in the crystallized microdomain structure (chi (c)<0.23), suggesting t he substantial difficulty of crystallization within the curved microdomain. The mechanism of morphology formation in the solution-cast samples is disc ussed by considering the competition between microphase separation and crys tallization during the solvent evaporation at each T-c and M-n.