Thermal annealing of roll-cast triblock copolymer films

Abstract

Polystyrene—polybutadiene—polystyrene triblock copolymers were roll-cast from toluene solutions to form globally oriented films. Microstructural changes following thermal annealing of films with cylindrical and lamellar morphology were monitored using two-dimensional small angle X-ray scattering, transmission electron microscopy and thermomechanical analysis. The microdomains in the unannealed films of cylindrical morphology were found to be assembled on a distorted hexagonal lattice, due to the roll-casting flow field. Thermal annealing significantly improved the alignment and packing of the cylinders, increased grain size, reduced the number of morphological defects and resulted in a 12% decrease in the area per junction. The microstructure of the unannealed films of lamellar morphology was observed to be composed of many small grains with low-angle helicoid surface twist boundaries. Annealing significantly reduced the number of grains and twist boundaries and resulted in a 7% decrease in the area per junction. Molecular models are presented for the relaxation of the chains during the annealing process in both cylindrical and lamellar morphologies based upon 2-D SAXS data and thermomechanical analysis.