Supported copper triflate as catalyst for the cationic polymerization of styrene

Abstract

Silica-supported copper triflate catalysts have been prepared and used in the heterogeneous cationic polymerization of styrene in an attempt to reduce the environmental hazards associated with the traditional vinyl polymerization catalyzed by homogeneous Lewis acid. Faster reactions and higher molecular weight polymers were observed compared to the homogeneous catalyst. However, the presence of active sites both within the pores and on the external surface, and the possible availability of different types of catalytic sites, leads to broad polymer molecular weight distribution. The catalysts exhibited both Lewis and Brønsted acidities due to the presence of residual moisture within Cu(OTf) 2, as well as the surface silanol groups of the silica and the methanol used as solvent in the catalyst preparation. Initiation occurs via a catalyst/cocatalyst process and water has proven to play a major role as the cocatalyst. Proton transfers from the growing polymer molecules to the initiating species or to the monomer represent the principal termination mechanism. The reuse of the catalyst was limited by the blocking of the pores by the polymer chains, reducing the diffusion of the monomer units to the active sites.