Polycarboxylic acids via catalytic hydrocarboxylation of polybutadienes

Abstract

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.