THERMAL ANNEALING OF ROLL-CAST TRIBLOCK COPOLYMER FILMS

Polystyrene-polybutadiene-polystyrene triblock copolymers were roll-ca st from toluene solutions to form globally oriented films. Microstruct ural 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 thermomechanica l analysis. The microdomains in the unannealed films of cylindrical mo rphology were found to be assembled on a distorted hexagonal lattice, due to the roll-casting flow field. Thermal annealing significantly im proved the alignment and packing of the cylinders, increased grain siz e, reduced the number of morphological defects and resulted in a 12% d ecrease in the area per junction. The microstructure of the unannealed films of lamellar morphology was observed to be composed of many smal l grains with low-angle helicoid surface twist boundaries. Annealing s ignificantly reduced the number of grains and twist boundaries and res ulted in a 7% decrease in the area per junction. Molecular models are presented for the relaxation of the chains during the annealing proces s in both cylindrical and lamellar morphologies based upon 2-D SAXS da ta and thermomechanical analysis. (C) 1997 Elsevier Science Ltd.