Graft copolymers as stabilizers of san dispersions in polyether-polyols and and ultimately in polyurethane foams

Several patents claim that thermoplastic particles, and particularly poly(styrene-coacrylonitrile) (SAN) particles, can be dispersed in liquid polyether-polyols, using a graft copolymer as a steric stabilizer. This paper reports another technique able to stabilize SAN (80 wt% styrene and 20 wt% acrylonitrile) dispersions in such a way that the in-situ generated stabilizer is very effective and as well defined as possible. Variations in the molecular characteristics of a double comb graft copolymer used as a steric stabilizer in dispersions of SAN particles in a liquid polyol allow dispersion properties, such as stability, particle size and viscosity to be controlled and optimized. Load bearing property of PU foams is best improved when they are modified by a stable dispersion of rather small SAN particles. These solid polymer/polymer dispersions are actually controlled by the double comb graft copolymer that stabilized the original solid/liquid system. When the mutual anchoring of the solid polymer phases is properly controlled, tear resistance and tensile strength of foams are improved, whereas elongation is kept at an acceptable level.