Hydration Mediation in Supported Aqueous-Phase Catalysis for Atom Transfer Radical Polymerization

Abstract

Hydrated sodium montmorillonite (Na-clay) and silica gel are used as solid supports for atom transfer radical polymerization (ATRP) of benzyl methacrylate and methyl methacrylate. The catalyst complexes of CuBr2 and CuBr with N,N,N′,N′,N″-pentamethyldiethylenetriamine, which are physically adsorbed on Na-clay and silica gel, are efficiently retained by the solid supports via small amounts of hydration. The supported aqueous-phase catalysis (SAPC) over Na-clay and silica produces catalyst-free polymers for activator generated electron transfer ATRP and conventional ATRP processes. The kinetics for the catalyst supported Na-clay and silica systems show that the polymerization proceeded only in the presence of hydrated catalyst support and ceased when the polymerization solution was separated from the hydrated catalyst support. In the case of Na-clay SAPC, the polymerization follows a linear first-order time–conversion plot and produces polymers with moderately narrow molecular weight distribution (MWD, Mw/Mn ≤ 1.30). However, for silica SAPC the first-order time–conversion plot is curved, indicating that the polymerization proceeds with termination and polymers exhibited broad MWD (Mw/Mn > 1.50). The poor performance of silica SAPC is attributed to the inefficient mobility of the catalyst and the nature of hydrogen bonding of the water molecules on its surface. The bilogarithmic plot of apparent rate constant kapp vs [I]0 in SAPC for ATRP indicates a zero order, suggesting that the polymerization is independent of the bulk initiator concentration, and the propagation is confined to the hydrated interface between the solid support and the organic phase.