Miniemulsion photopolymerization in a tubular reactor

Résumé

The synthesis of polyurethane (PU)/(meth)acrylics by miniemulsion photopolymerization in a continuous tubular reactor, at room temperature, for their application as a pressure sensitive adhesives was studied. In a comprehensive study of photoinitiation conditions (photoinitiator concentration and incident light irradiance) and residence time on photopolymerization kinetics and hybrid polymer microstructure (gel fraction, sol molecular weight) it was found that this process is more flexible than the thermaly induced semicontinuous miniemulsion polymerization, allowing the synthesis of a wide range of polymers with different characteristics (gel fraction and sol molecular weights) and performance (PSAs) using the same PU/(meth)acrylics formulation. In this system, the hybrid was formed by free radical polymerization and addition polymerization, leading to complex polymer architecture. Using asymmetric flow field flow fractionation to analyze the whole sample molecular weight distribution it was shown that PU/(meth)acrylic latexes undergo spontaneous formation of nanogels within the latex particles during storage at room temperature. A complete study of the effect of photoinitiation conditions (photoinitiator type and concentration and incident light irradiance) on the kinetics, microstructure and adhesive properties was carried out. It was shown that the kinetics and the microstructure of the hybrid polymer can be widely modified by changing the radical generation conditions using different photoinitiator types and concentrations and different incident light irradiances. It was found that by controlling the radical initiation conditions the whole spectrum of adhesive properties can be achieved (from liquid-like to highly cohesive). The scale up of the tubular reactor for miniemulsion polymerization of hybrid PU/(meth)acrylics was performed by increasing the reactor diameter from 1mm to 5mm and 10 mm. In both cases full monomer conversion was achieved in relatively short residence times (15 and 20 min).