Pd/charcoal-catalysed cleavage of benzyl ester protecting groups in poly(benzyl acrylate) and poly(benzyl methacrylate)

Abstract

The cleavage of benzyl protecting groups of poly(benzyl acrylate), poly(benzyl malolactonate) and poly(benzyl methacrylate) by Pd/charcoal-catalysed hydrogenolysis was investigated in order to show the consequences of chemical modification on the molecular structures of the resulting polymeric compounds. It is shown that such catalytic cleavage is a general reaction that depends very much on the structure of the porous charcoal and on the location of the Pd-metal catalyst, which can be either at the surface or well inside the pores, or both. The rate of cleavage depends on many factors, namely nature of the parent polyacid backbone, stirring rate, solvent, relative amounts of poly(benzyl ester) and of catalytic system, etc. However, molecular weights, molecular-weight distribution and the origin of the catalytic system seem to be the main factors. Data confirm that partial catalytic hydrogenolysis can lead to the formation of blocky acid/ester copolymers or to mixtures of homopolymers depending on the structure of the Pd/charcoal catalytic system.