Process for the preparation of nitrile rubbers

Abstract

Process for the preparation of a nitrile rubber comprising: —subjecting at least one α,β-unsaturated nitrile, at least one conjugated diene and, optionally, one or more further copolymerizable monomers, to emulsion polymerization, in the presence of at least one alkyl thiol containing from 12 to 16 carbon atoms and at least three tertiary carbon atoms and having the sulfur bound to one of said tertiary carbon atoms, at a pH ranging from 7 to 10, preferably from 8 to 9, obtaining a latex; —subjecting said latex to coagulation, in the presence of at least one metal sulfate selected from magnesium, sodium, potassium, preferably magnesium, at a temperature higher than or equal to 30° C., preferably ranging from 40° C. to 60° C., obtaining a coagulated nitrile rubber: —subjecting said coagulated nitrile rubber to washing with water, in the presence of at least one inorganic base, selected from sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, lithium hydroxide, preferably potassium hydroxide, at a pH higher than or equal to 10, preferably ranging from 11 to 12. The nitrile rubber thus obtained is capable of giving vulcanizable elastomeric compositions having a high vulcanization rate and a good vulcanization yield. Furthermore, said elastomeric compositions cause a low fouling of the molds and can consequently be advantageously used in injection molding processes.