Styrene butadiene rubbers (SBR) have been modified upon catalytic addition of carbene groups (:CHCO2Et) from ethyl diazoacetate (N2CHCO2Et) under very mild conditions using copper catalysts. The modified rubbers contained 3-5% (w/w) of carboxylate groups and displayed hydrodynamic properties very similar to those of the starting material, evidencing the lack of chain scission processes. Preliminary studies on the effect of the presence of the carboxylate functionality on some physical properties of the rubbers are reported, and the morphology of their blends with nylon-6 is also described.