Elastomer production

Claim 1

IN A PROCESS FOR THE PRODUCTION OF AN ELASTOMERIC MATERIAL FROM A HOMOGENEOUS COMPOSITION COMPRISING FROM 50% TO 95% BY WEIGHT OF THE PRECURSORS OF A CROSS-LINKED POLYURETHANE WHICH, WHEN REACTED ALONE IN THE ABSENCE OF ETHYLENICALLY UNSATURATED MATERIAL, ARE CAPABLE OF FORMING AN ELASTOMERIC POLYURETHANE HAVING A GLASS-RUBBER TRANSITION TEMPERATURE OF 25*C OR LESS, AND FROM 50% TO 5% BY WEIGHT OF AT LEAST ONE POLYMERISABLE ETHYLENICALLY UNSATURATED MATERIAL, IN WHICH PROCESS THE REACTION OF THE POLYURETHANE PRECURSORS IS SUBSTANTIALLY COMPLETED BEFORE POLYMERISATION OF THE ETHYLENICALLY UNSATURATED MATERIAL IS ALLOWED TO PROCEED TO THE EXTENT THAT THE POLYMER SO PRODUCED FORMS A SEPARATE PHASE AND IN WHICH POLYMERISATION OF THE ETHYLENICALLY UNSATURATED MATERIAL IS THEREAFTER COMPLETED, THE IMPROVEMENT WHICH COMPRISES USING IN THE PROCESS AN ETHYLENICALLY UNSATURATED MATERIAL WHICH CONTAINS AT LEAST ONE POLYFUNCTIONAL ETHYLENICALLY UNSATURATED MATERIAL AND IS SELECTED SO AS TO PRODUCE, AFTER POLYMERISATION, A CROSS-LINKED POLYMER HAVING ON AVERAGE A MOLECULAR WEIGHT BETWEEN CROSS-LINKS OF NOT GREATER THAN 2,500.