Hybrid miniemulsion photopolymerization in a continuous tubular reactor-A way to expand the characteristics of polyurethane/acrylics

Waterborne polyurethane (PU)/acrylic hybrids were synthesized by photoinitiated miniemulsion polymerization carried out in a continuous tubular reactor. Almost complete conversion was achieved in short residence time (<5 min) using low concentrations of photoinitiator (<0.48 wt%) and modest incident light irradiance (<7 mW/cm(2)). The hybrid was formed by simultaneous free radical polymerization and addition polymerization, through the reaction of the isocyanate groups of the PU with the hydroxyl groups of the acrylic monomers. It was found that this process is more flexible than the classical semicontinuous miniemulsion polymerization allowing the synthesis of a wide range of polymer characteristics (gel fraction and sol molecular weights) using the same PU/acrylics formulation. (C) 2012 Elsevier B.V. All rights reserved.