Emulsion polymerization process

Claim 1

A PROCESS OF MAKING A RUBBERY BUTADIENEACRYLONITRILE COPOLYMER HAVING A CONTENT OF METHYL ETHYL KETONE-INSOLUBLE GEL OF FROM 40 TO 80%, SAID GEL HAVING A SWELLING INDEX, MEASURED IN METHYL ETHYL KETONE, OF FROM 8 TO 35, AND A MOONEY VISCOSITY, MEASURED AT 212* F., OF FROM 40 TO 80, EACH OF SAID VALUES FOR GEL CONTENT, GEL SWELLING INDEX AND MOONEY VISCOSITY BEING DETERMINED ON A SAMPLE WHICH HAS BEEN MASSED BY MILLING FOR 5 MINUTES AT 360* F., WHICH COMPRISES SUBJECTING A MIXTURE OF BUTADIENE AND ACRYLONITRILLE TO AQUEOUS EMULSION POLYMERIZATION, INITIATING POLYMERIZATION OF SAID BUTADIENE AND ACRYLONITRILE IN THE ABSENCE OF A CROSS-LINKING AGENT, THEREAFTER ADDING FROM 0.7 TO 1.5% BY WEIGHT, BASED ON THE BUTADIENE AND ACRYLONITRILE, OF DIVINYLBENZENE AT A TIME WHEN FROM 10 TO 35% OF THE ORIGINAL MONOMER MIXTURE HAS BEEN CONVERTED TO POLYMER, CONTINUING THE POLYMERIZATION, AND STOPPING THE POLYMERIZATION AT A TIME WHEN AT LEAST 60% BUT NOT MORE THAN 80% OF SAID ORIGINAL MONOMER MIXTURE HAS BEEN CONVERTED TO POLYMER.