Rheological study of UV curable pigmented coating containing hydroxyl and mercaptan end groups hyperbranched polymers

A dynamic rheological technique (photorheometery) was used to observe the evolving rheological properties of the hydroxyl and mercaptan end groups of the polymers during the photopolymerization system. Gel time, elastic modulus and viscous modulus were evaluated by this technique. A UV curable coating based on Epoxy acrylate with a PVC of 10% was investigated containing different percentages of two kind of polymers. Results show that hydroxyl end groups caused a decreased gel time and increased elastic modulus until %3wt of hyperbranched polymers. However, the mercaptan end groups had further effect on gel time most probably because there were two kinds of mechanisms for polymerization which are photopolymerization regarding to photoinitiator and click-polymerization regarding to mercaptan groups. Click polymerization improved crosslink density which caused an increase to elastic modulus. Thus, mercaptan end groups had more significant decreasing effect on gel time and viscoelastic moduli.