The morphology of alkyd/acrylate latexes produced via hybrid miniemulsion polymerization: grafting mechanisms

Abstract

The ultimate objective of hybrid miniemulsion polymerization is to produce a water-based crosslinkable coating through in-situ grafting of a free-radical growing acrylic polymer with an unsaturated resin. Certain authors have reported low grafting while others have reported higher. This paper explores the factors that influence the grafting tendencies of these systems. Methacrylates such as methyl methacrylate (MMA) have a sterically hindered radical center that lowers its reactivity towards unsaturated resin. This steric hindrance from the methyl group forces grafting of this type of monomer to occur by abstraction of a hydrogen allylic to a resinous double bond. This chain transfer produces a relatively inactive radical on the resin that reduces the grafting efficiency. Grafting occurs in this type of system through termination of living PMMA chains with that radical produced on the resin. For hybrid systems involving an acrylate monomer such as butyl acrylate (BA), virtually complete grafting with alkyd was observed. This is due to the uninhibited BA radical center allowing the molecule to directly add through a resin double bond.