Urea additives for sulfur vulcanizable polymers

Claim 1

A sulfur vulcanizable rubber selected from the group consisting of natural rubber and synthetic homopolymers and copolymers of conjugated dienes having incorporated therein 0.25 to 10 parts by weight per 100 parts by weight of rubber of a urea having the following structural formula ##STR7## wherein R is selected from the group consisting of saturated or olefinic divalent aliphatic radicals having 1 to 7 carbon atoms, saturated or olefinic divalent cyclic aliphatic radicals having 5 to 7 carbon atoms, arylene radicals having 6 to 10 carbon atoms and the radical ##STR8## which together with the ##STR9## radical forms a hydantoin ring wherein R 3 and R 4 are selected from the group consisting of hydrogen, alkyl radicals having 1 to 4 carbon atoms, cycloalkyl radicals having 5 to 6 carbon atoms, aralkyl radicals having 7 to 10 carbon atoms and aryl radicals having 6 to 10 carbon atoms or R 3 and R 4 can be joined to form with the attached carbon atom a hydrocarbon ring containing 5 to 6 carbon atoms, and wherein R 1 and R 2 are selected from the group consisting of alkyl radicals having 1 to 20 carbon atoms, cyanoalkyl radicals having 2 to 21 carbon atoms, cycloalkyl radicals having 5 to 20 carbon atoms, aralkyl radicals having 7 to 20 carbon atoms and aryl radicals having 6 to 20 carbon atoms and wherein R 1 and R 2 can be joined through a member of the group consisting of -- CH 2 -- , -- O -- and -- S -- to constitute with the attached nitrogen atom a heterocyclic ring.