Electrokinetic and mechanical characterization of UV induced crosslinked acrylic copolymers

Functionalized copolymers for using as UV curable coatings were synthesized from three different monomers; methylmethacrylate, n-butylacrylate and gly cidyl-methacrylate. The synthesis of functionalized copolymers consisted of two steps, the polymerization and the functionalization, and could be perf ormed to high conversion rates as proved by gaschromatographical residual m onomer detection. The synthesized coatings varied both in the polymer backb one composition as well as in the crosslink density. UV curing was performe d in the presence of a commercially available photoinitiator system. The measured zeta (xi) potential time dependence allows to study the swelli ng kinetics of the synthesized coatings in water. Physicochemical surface p roperties of the coatings were investigated by measuring the xi -potential- pH dependence. The surfaces display a mostly hydrophobic character. Dependi ng on the polymer composition, a change of the hydrophobic surface characte r towards a slightly acidic one was detected. For the various coatings, str ucture-property relationships could be observed. The isoelectric point, a m easure of the surface acidity, decreases with increasing crosslink density, for instance, which indicates an increase in the amount of dissociable aci dic surface functionalities. This can be attributed to lowered flexibility of the material. An analogous trend could be observed for the water uptake: the higher the crosslink density, the lower the water adsorption. With the technical applications in mind, some relevant data on the mechanic al properties were obtained, as measure of hardness, flexibility and adhesi on to bonder-plates. The expected correlation for the pendulum hardness and the Erichsen cupping (a measure for the flexibility) could be found. The i ncreased glass transition temperatures leads to an enhanced hardness and a lowered flexibility. The cross-cut test of the polymeric coatings on bonder -plate surfaces showed medium to very good adhesion. The results indicate t he existence of an optimal crosslink density as well as T-g range for the i nvestigated copolymer system. (C) 1999 Elsevier Science S.A. All rights res erved.