Microphase separation vs crystallization in polystyrene-b-polybutadiene-b-poly(ε-caprolactone) ABC triblock copolymers

The melting behavior as well as the crystallization kinetics of a series of polystyrene-b-polybutadiene-b-poly(6-caprolactone) ABC triblock copolymers was investigated by differential scanning calorimetry (DSC). The studies were performed as a function of annealing time at high temperature (150 degreesC), maintaining invariable the crystallization conditions. While a copolymer with only 16 wt % PCL does not show significant changes with the annealing time, it influences strongly the melting behavior and crystallization kinetics of copolymers with higher PCL content. Thus, higher melting points and degree of crystallinity can be observed by increasing annealing time, suggesting the results show a clear "conflict" between microphase separation and crystallization. This is more evident when the thermodynamic force to form spherulites and the thermodynamic force to maintain the microphase morphology formed in the melt compete. The analysis of the crystallization kinetics through the Avrami theory demonstrated that when the nucleation step proceeds heterogeneously, the Avrami exponent effectively reflects the dimensionality of crystal growth.