In Situ Preparation of Impact-Resistant Polystyrene

Abstract

Our research intends to prepare an “in situ” impact-resistant polystyrene with improved mechanical properties by bulk and suspension polymerization of styrene in the presence of dissolved rubber. Two specimens of three block copolymers of the styrene-butadiene-styrene type, having different polystyrene content and different molecular weight, have been used as dissolved materials. From our experiments it follows that the polymerization rate is strongly influenced by the amount of rubber contained in the original solution; it is possible to obtain materials containing up to 20 wt% of polybutadiene; it is reasonable to foresee that this value could be increased by changing the molecular weight of the co-polymer and/or the chain block length; the Young modulus decreases and the impact strength increases with the rubber content of the in situ prepared blends, independently of the polymerization technique; polyvinyl alcohol has been found as the most effective suspending agent; the morphology of our materials is strongly different from that of commercial high impact polystyrene. Instead of a random and discontinuous distribution of large domains of the elastic component in the rigid matrix, we have a regular poly-butadiene network. In conclusion, our results show that impact-resistant polystyrene can be prepared by the polymerization of styrene containing in-solution block copolymers with the outside blocks sufficiently compatible with the monomer to give an homogeneous distribution of the rubbery component. A good balance between modulus and strength can be obtained, and it can be foreseen that results of practical interest could be achieved when copolymer with appropriate molecular weight and block length are used.