2. A process according to claim 1 wherein the reaction mixture contains a filler.

3. A process according to claim 2 wherein the filler is carbon black.

4. A process according to claim 3 wherein the reaction mixture contains 40 to 120 percent of carbon black, based on the elastomer.

5. A process according to claim 1 wherein the reaction mixture contains an extender oil.

6. A process according to claim 5 wherein the reaction mixture contains 10 to 100 percent by weight of a predominantly aromatic or naphthenic type extender oil, based on the elastomer.

7. A process according to claim 1 wherein the reaction mixture contains both an extender oil and a filler.

8. A process according to claim 1 wherein the elastomer is a polydiene.

9. A process according to claim 8 wherein the polydiene is a member of the group consisting of polybutadienes, polyisoprenes, and copolymers of butadiene and styrene.

10. A process according to claim 1 wherein the reaction temperature is 120* to 190* C.

11. A process according to claim 1 wherein the reaction mixture contains 1 to 5 percent by weight of water, based on the elastomer.

12. A process according to claim 11 wherein the reaction mixture contains 1.5 to 3 percent by weight of water, based on the elastomer.

13. A process according to claim 1 wherein the reaction mixture contains about 0.001 to 0.1 percent by weight of the metallic compound catalyst, based on the elastomer.

14. A process according to claim 1 wherein the reaction mixture contains as the catalyst a salt of aluminum, trivalent iron, tin, boron, zinc, or of trivalent or tetravalent titanium.

15. A process according to claim 14 wherein the salt is a halide salt.

16. A process according to claim 15 wherein the reaction mixture contains FeCl3 or AlCl3 as catalyst.

17. A process according to claim 1 wherein the reaction mixture contains about 0.04 to 0.9 percent by weight of the base as cocatalyst, based on the elastomer.

18. A process according to claim 1, wherein the base co-catalyst is a member of the group consisting of alkali-metal and alkaline earth alcoholates, and primary, secondary, and tertiary amines.

19. A process according to claim 18 wherein the co-catalyst base is an amine.

20. A procesS according to claim 19 wherein the amine is a primary aromatic amine or diamine containing 6 to 30 carbon atoms.

21. A process according to claim 20 wherein the amine is p-phenylenediamine, benzidine or p,p''-diaminodiphenylmethane.

22. A process according to claim 1 wherein the starting elastomer has a molecular weight of between 10,000 and 50,000 and is a member of the group consisting of polybutadienes, polyisoprenes and copolymers of butadiene and styrene; the reaction is conducted for up to about 20 minutes at a temperature of 120* to 190* C; the reaction mixture contains a metallic compound catalyst selected from the group consisting of a salt of aluminum, trivalent iron, tin, boron, zinc, or trivalent or tetravalent titanium and an amine as the co-catalyst.

23. A process according to claim 22 wherein the reaction mixture contains about 0.001 to 0.1 percent by weight of a halide salt as the catalyst and 0.04 to 0.9 percent by weight of a primary aromatic amine or diamine containing 6 to 30 carbon atoms as the cocatalyst, based on the elastomer.

24. A process according to claim 1 wherein the molecular weights of the solid hydrocarbon elastomers are between 10,000 and 500, 000.

25. A process according to claim 1 wherein the molecular weights of the solid hydrocarbon elastomers are between 50,000 and 250, 000.

26. A process according to claim 22 wherein the co-catalyst is p-phenylenediamine, benzidine or p,p''-diaminodiphenylmethane.

27. A process according to claim 23 wherein the co-catalyst is p-phenylenediamine, benzidine or p,p''-diaminodiphenylmethane.