Polycarboxylic acids via catalytic hydrocarboxylation of polybutadienes

Abstract

Polybutadienes with various different microstructures have been hydrocarboxylated using different homogeneous catalytic systems. With [PdCl₂(PPh₃)₂]–SnCl₂ as the catalyst, high conversions of the pendant double bonds to terminal carboxylic acids are obtained and the backbone double bonds are unreactive. Using PdCl₂, CuCl₂ and O₂ at room temperature and 1 atm (101 325 Pa) pressure a non-selective reaction occurs so that carboxylic acid groups are introduced at the backbone double bonds as well as on the terminal or internal C atoms of the pendant double bonds. The reactivity order, backbone > terminal > internal, is interpreted in terms of a generally higher stability for secondary alkyl intermediates, provided there is no chain branching at the C atom a to the point of attachment to the metal. Using sequential reactions catalysed first by [PdCl₂(PPh₃)₂]–SnCl₂ then by [PdCl₂(PPh₃)₂] in the presence of excess PPh₃, a polymer is obtained containing no double bonds, but carboxylic acid groups attached to the terminal C atoms of the pendant double bonds and to the backbone of the polymer. Gel-permeation chromatography indicates that neither chain scission nor extensive crosslinking takes place during the reaction. The use of one of the polymers for preventing the uptake of water by balsa wood is described, and evidence is presented that the polymer is not useful for the conservation of waterlogged wood.