INTERFACIAL MODIFICATION OF POLYMER BLENDS - THE EMULSIFICATION CURVE.2. PREDICTING THE CRITICAL CONCENTRATION OF INTERFACIAL MODIFIER FROM GEOMETRICAL CONSIDERATIONS

Geometrical considerations about macromolecular size have been used in order to make a critical analysis of the minimum amount of block copo lymer needed to saturate the interface in the melt mixing of immiscibl e polymer blends. For the case of dispersed spherical domains an expre ssion has been developed (Equation (8)) which contains only molecular parameters such as the number of bonds, the characteristic ratio and t he composition of the block copolymer used to compatibilize the blend. The shell surrounding each particle was divided into small pseudocubi cal elements. the unperturbed size of the matrix-like blocks of the co polymer was considered as representative of the size of these elements . Comparison has been made with experimental data regarding an ethylen e-propylene rubber dispersed in a polystyrene matrix. That blend was c ompatibilized with styrene-hydrogenated butadiene copolymers with diff erent molecular weights and architecture (diblock and triblock). The e xperimental data allow a quantitative assessment of the number of comp atibilizer chains per unit cubical element corresponding to the onset of interfacial saturation: this value was found to depend on the copol ymer architecture but is substantially independent of the copolymer mo lecular weight. Copyright (C) 1996 Elsevier Science Ltd.