Influence of the crystallization temperature on the microphase morphology of a semicrystalline ABC triblock copolymer

The microphase morphology of a polystyrene-block-polybutadiene-block-poly(epsilon-caprolactone) SBC triblock copolymer is studied through transmission electron microscopy. Even though crystallization of the PCL block takes place well below the PS glass transition, lamellar microphases and the formation of well-defined spherulites are observed. The typical long-range order normally obtained for amorphous triblock copolymers is not obtained in the SBC triblock copolymer, The morphology of a polystyrene-block-poly(epsilon-caprolactone) diblock copolymer was also observed and compared with the triblock copolymer, To investigate whether the crystallization temperature (T-c) is a parameter influencing the final morphology, samples of the triblock copolymer were crystallized at 45 and 42 degrees C. This reduction in T-c results in a morphological transition from a simple lamellar morphology (PS, PB, and PCL form layers), which we call lamellar-lamellar (ll), to a lamellar-cylindrical (lc)-morphology with PS and PCL layers and PB cylinders at the PS/PCL boundary. From these changes, combined with the observation of well-defined spherulites in both cases, we can deduce the orientation of the PCL chains in the crystalline regions as being perpendicular with regard to the block copolymer interfaces.