Annealing effects on the elastic properties of sphere-forming ABA and ABC triblock copolymers

Annealing effects on the elastic behavior of sphere-forming polystyrene-block-polyisoprene-block-polystyrene (SIS) and polystyrene-block- polyisoprene-block-poly(2-vinylpyridine) (SIP), annealed in a cone-plate attached to a rheometer at 150°C with and without additional shear, are examined by dynamic mechanical analysis performed at 70°C. Plateau modulus G_N obtained at 70°C rapidly increased within the first one hour, while G_N very gradually increased at longer times. By comparing the data with and without additional shear, the initial increase of G_N is attributed to increase in restoring force of the lattice caused by the relaxation of lattice distortion. The gradual increase at longer times is attributed to reformation of network structure by reentrant of pulled-out end blocks into the spherical domains since it was faster for SIS than SIP; S and P chains are immiscible with each other so that it takes longer time for SIP to reform the network structure. Contribution of pull out of end blocks and network reformation on elastic properties for molded film are not so large.