It is well known that styrene homopolymers and copolymers of styrene and acrylonitrile have poor impact strength. In order to increase this impact strength, rubber is added to these styrenic polymers where it acts as a reinforcing agent. A widely used method comprises polymerizing styrene in the presence of an unsaturated rubber. The products obtained by this method are more stable and have superior properties when compared with products prepared by other methods, such as blending or milling.
One usual technique for preparing rubber-reinforced styrenic resins consists of grafting chains of homo- or copolymers of styrene onto a rubber, either by an all emulsion process or an all suspension process or a mass-suspension process. Such techniques present an economic problem, as the manufacture of these reinforced styrenic resins depends on rubber supplies.
In order to decrease the costs of these reinforced styrenic resins, and to obviate some drawbacks of the prior processes, it has been proposed to prepare rubber reinforced styrenic resins by forming the rubber particles in situ in the presence of a rigid styrenic resin. The process comprises contacting a polystyrenic matrix and a monomer or a mixture of monomers forming a rubbery polymer or copolymer by polymerization and then suspension polymerizing said monomer(s) with formation of a rubber partly grafted to the matrix. The production of rubber reinforced styrenic resins by this method is a batch process. Moreover, the beads obtained by this suspension method must be washed, centrifuged and dried.
There exists a need in the art, therefore, for a less expensive method for producing rubber reinforced styrenic resins.