Improvements in or relating to modified styrene compositions

Styrene and a natural resin acid or a polyhydric alcohol ester thereof e.g. rosin, tall oil, run congo, ester gum and congo ester are interpolymerized in the presence of a Friedel-Crafts catalyst e.g. boron fluoride, stannic chloride, and aluminium chloride. Styrene comprises 75 to 99 per cent. of the mixture and may be added portionwise and the process may be performed in bulk or in a solvent, e.g. benzene. The mixture is heated preferably between 100 DEG C. and the reflux temperature while the catalyst may be added dropwise in a benzene solution to the mixture. The product is purified by distillation in a stream of carbon dioxide. In a modification drying or semi-drying oils may be added before or after the interpolymerization and esters may be prepared by reacting the interpolymers with polyhydric alcohol or a partial ester of polyhydric alcohol and a drying or semi-drying oil fatty acid.