RAFT-mediated polystyrene-clay nanocomposites prepared by making use of initiator-bound MMT clay

Abstract

The initiator 2,2′-azobis(2-(1-(2-hydroxyethyl)-2-imidazolin-2-yl)propane)dihydrochloride monohydrate (VA060) was used to surface-modify sodium montmorillonite clay (Na-MMT). The obtained organically modified clay was then used as a macro-initiator in the preparation of polystyrene-clay nanocomposites by in situ free radical polymerization of styrene in bulk. The polymerization was carried out in the presence of various reversible addition-fragmentation chain transfer (RAFT) agents: 1,4-phenylenebis(methylene)dibenzenecarbodithioate (PCDBDCP), didodecyl-1,4-phenylenebis(methylene)bistrithiocarbonate (DCTBTCD) and 11-(((benzylthio)-carbonothioyl)thio)undecanoic acid (BCTUA). All of the nanocomposites prepared were found to have intercalated morphologies. In the absence of RAFT agents, typical uncontrolled free radical polymerization occurred, giving polystyrenes with high molar masses and high polydispersity indices. In contrast, when the polymerization was conducted in the presence of any of the RAFT agents, the polymerization was found to occur in a controlled manner, as the polystyrene-clay nanocomposites obtained contained polymer chains of narrow polydispersities. The influences of clay loading and molar mass on thermal stability of the polystyrene-clay nanocomposites were investigated. Increases in the clay loading or the molar masses resulted in improvement of the thermal stability of the nanocomposites.