alkylacrylate rubbers are preferably ethylacrylate rubber or butylacrylate rubber and most preferably butylacrylate rubber suitable alkylacrylate rubber graft copolymers include acrylonitrile ethylacrylate styrene acrylonitrile butylacrylate styrene and methyl methacrylate butylacrylate styrene graft copolymers the butylacrylate rubbers may be uncross linked or cross linked preferably partially cross linked small lt 10 amounts of butadiene may be used to improve performance monomers containing more than one polymerisable and double bond may be copolymerised with the butylacrylate for cross linking the butylacrylate rubber preferred examples of cross linking monomers are esters of unsaturated monocarboxylic acids containing from 3 to 8 carbon atoms and unsaturated monohydric alcohols containing from 3 to 12 carbon atoms or saturated polyols containing from 2 to 4 oh groups and from 2 to 20 carbon atoms such as ethylene glycol dimethylacrylate and allyl methacrylate polyunsaturated heterocyclic compounds such as trivinyl and triallyl cyanurate and isocyanurate tris acryloyl s triazines particularly triallyl cyanurate and polyfunctional vinyl compounds such as di and tri vinyl benzenes and also triallyl phosphate and diallyl phthalate preferred cross linking monomers are allyl methacrylate ethylene glycol dimethacrylate diallyl phthalate and heterocyclic compounds containing at least three ethylenically unsaturated groups particularly preferred cross linking monomers are the cyclic monomers triallyl cyanurate triallyl isocyanurate trivinyl cyanurate triacryloyl hexahydros triazine and triallyl benzenes the cross linking monomers are preferably used in quantities of from 0 02 to 5 by weight more preferably from 0 05 to 2 by weight based on the butylacrylate rubber in the case of cyclic cross linking monomers containing at least three ethylenically unsaturated groups it is advantageous to limit the quantity to lt 1 by weight of butylacrylate rubber preferred copolymerisable ethylenically unsaturated monomers for the butylacrylate rubber which in addition to the acrylic acid esters may optionally be.