Co-continuous morphologies in polymer blends with SEBS block copolymers

Stable co-continuous morphologies are found over a wide composition range i n blends of styrene/(ethylene-butylene) based block copolymers (SEBS) and p olypropylene (PP) when they are processed below the block copolymer's order -disorder transition (ODT), i.e. when the block copolymers are microphase-s eparated. Blending at higher temperatures, i.e. when the block copolymer sh ows a single-phase melt, also leads to a reasonably wide composition range of co-continuity but when annealing takes place at these temperatures the b lends show an increase in their phase domains and the composition range dec reases significantly. Annealing of the co-continuous PP/SEBS blends when th e block copolymers are microphase-separated hardly influences the phase siz es and composition range. Blending the same block copolymers with polymethy l methacrylate or polyoxymethylene, leading to blends with much higher inte rfacial tensions, results in a much smaller composition range of co-continu ous morphologies than was found in the PP/SEBS blends, whatever the process ing temperature be. It is demonstrated that breakup and retraction can be s everely limited or even stopped at lower blending temperatures, therefore f ulfilling the condition for stability of co-continuous morphologies. The (n on-)breakup or (non-)retraction behaviour of elongated structures strongly depends on a complex combination of parameters, including phase size, yield stress and interfacial tension. Therefore the formation of stable co-conti nuous morphologies also strongly depends on these parameters. (C) 1999 Else vier Science Ltd. All rights reserved.