Siloxane terpolymers as compatibilizers for polymer blends

Abstract

Siloxane containing copolymers and graft terpolymers are used as compatibilizers for model immiscible polar/non polar blend systems. Compatibilizers generally consisted of a siloxane backbone containing various amounts of polyether and alkyl grafts with controlled molecular weights. Influence of structural and compositional variations and additive concentrations on the interfacial tensions of three, low molecular weight model blend systems, polyolefin/polyether, polypropylene/polyether and polypropylene/polyamide were measured by either the spinning drop or sessile drop methods. Stability of the dispersions and average sizes of the dispersed particles were also determined by optical microscopy. It has been shown that these types of siloxane graft terpolymers were more effective in reducing the interfacial tensions than conventional AB type block systems with no siloxane in their structures. Molecular design and architecture of the siloxane compatibilizers and a proper balance between non-polar and polar grafts played important roles in their efficiencies. Additives with longer siloxane backbone seemed to be more effective in reducing the interfacial tension. In polypropylene/polyether system a linear relationship between the reduction in the interfacial tension and the reduction in the average particle size of the dispersed phase was found. Dispersions formed were very stable even at fairly high processing temperatures.