DEFORMATION AND TOUGHNESS OF POLYMERIC SYSTEMS .6. CRITICAL THICKNESSOF DILUTED ENTANGLEMENT NETWORKS

Following Kramer et al. who compared the maximum local draw ratio insi de craze fibrils or shear deformation zones for different types of net work structures, here the critical thickness (ID(c)), below which appa rently brittle amorphous glassy polymers demonstrate a macroscopic dra w ratio comparable with the high values determined on a microscopic sc ale, is studied for two - principally different - types of physical ne tworks. The value of ID(c) is determined for network structures based on polystyrene-poly(2,6-dimethyl-1,4-phenylene ether) (PS-PPE) blends. Two types of networks are compared obtained via blending high molecul ar weight PPE with either (i) a (standard) high molecular weight PS (P S(h)) or (ii) an extremely low molecular weight PS (PS(l)). In contras t to PS(h) PS1 cannot contribute to the entanglement network structure of the blend since the molecular weight falls well below the entangle ment molecular weight of PPE and, consequently, it can be considered a s a (glassy) solvent for PPE. The critical thickness of two network st ructures with the same network density but with different values of th e natural draw ratio (lambda(max)) is experimentally determined via ad dition of (non-adhering) core-shell rubbers. ID(c) proves to be invers ely proportional to the natural draw ratio of the network structure. T he simple energy-based model for the prediction of ID(c) quantitativel y explains the differences found.