Confinement of elastomeric block copolymers via forced assembly coextrusion.

Forced assembly processing provides a unique opportunity to examine the effects of confinement on block copolymers (BCPs) via conventional melt processing techniques. The microlayering process was utilized to produce novel materials with enhanced mechanical properties through selective manipulation of layer thickness. Multilayer films consisting of an elastomeric, symmetric block copolymer confined between rigid polystyrene (PS) layers were produced with layer thicknesses ranging from 100 to 600 nm. Deformation studies of the confined BCP showed an increase in ductility as the layer thickness decreased to 190 nm due to a shift in the mode of deformation from crazing to shear yielding. Postextrusion annealing was performed on the multilayer films to investigate the impact of a highly ordered morphology on the mechanical properties. The annealed multilayer films exhibited increased toughness with decreasing layer thickness and resulted in homogeneous deformation compared to the as-extruded films. Multilayer coextrusion proved to be an advantageous method for producing continuous films with tunable mechanical response.