Polybutadiene having varying degrees of 1,4 and 1,2 units (0 - 100% cis, 14 - 60 % trans, 20-88 % pendant carbon-carbon double bonds) have been reacted with carbon monoxide in the presence of water and palladium based catalysts to give new polymers in which the double bonds are hydrocarboxylated. When using [PdCl2(PPh3)2]/SnCl2 as catalysts, very high regiospecificities can be obtained with only the double bonds pendant from the chain being hydrocarboxylated. When using PdCl2 as catalyst, in the presence of CuCl2 and O2, hydrocarboxylation takes place both at the pendant carbon-carbon double bonds and back bone carbon-carbon double bonds. Complete hydrocarboxylation of all the carbon-carbon double bonds in polybutadiene can be carried out by sequential catalytic reaction i.e., catalysis by [PdCl2(PPh3)2]/SnCl2 followed by (recatalysis) [PdCl2(PPh3) 2]/PPh3. A new method based on 1H and 13C n.m.r. has been developed to characterise polybutadienes and their hydrocarboxylated products. The hydrocarboxylation reaction catalysed by [PdCl2(PPh3) 2]/SnCl2 is truly homogeneous although catalytic decomposition is a problem because there exists a small temperature window between the onset of catalysis and the onset of catalytic decomposition. Unlike the starting materials the products, which are solids with melting points well above the room temperature are soluble in organic solvents or dilute base and have been shown to have corrosion inhibition and wood preservation properties.