Making cross-linked styrene polymer foam

Claim 1

Method for the preparation of synthetic resinous thermoplastic products which comprises providing an acid-containing resinous polymer of an alkenyl aromatic monomer having copolymerized therewith at least about 60 percent by weight of at least one monomer of the Formula: ##STR10## wherein G is selected from the group consisting of hydrogen and methyl and Ar is an aromatic radical, including various alkyl- and halo-ring-substituted aromatic units, of from 6 to about 10 carbon atoms; with acid-providing monomer that is copolymerizable with styrene of at least one other monomer of the Formula: ##STR11## wherein Z is selected from the group consisting of hydrogen, alkyl radicals that contain not more than about 4 carbon atoms and carboxyl units when X is devoid of any carboxylating attachments; and X is a monoethylenically unsaturated substituent selected from the group consisting of methylene, alkenyl units containing from 2 to about 5 carbon atoms and, when Z is not carboxyl, carboxylated methylene and monocarboxylated alkenyl and alkene units containing from 2 to about 5 carbon atoms; the same having any further balance, if any, of copolymerized ethylenically unsaturated components, monomers and elastomeric natural or synthetic rubbers of at least one member of the class of same that are copolymerizable with styrene; feeding and passing through a mixing, malaxating extrusion apparatus acid-containing polymer, operating the extrusion apparatus at a temperature of between about that of the heat softening temperature of said polymer and that of the decomposition temperature of the polymer; and at one or more points within the apparatus at about or between its feed point and the point of extrudate discharge therefrom, incorporating into said polymer mass passing through said apparatus an effective interconnecting and network-building additament quantity of a cross-linking agent that is reactive with the free carboxyl entities in said polymer whereby to cross-link said mass of polymerizate material therein; and finally discharging said cross-linked mass of polymer material from said extruder apparatus.