Catalyst effect on the crosslinking kinetics of a fluorine containing polyurethane network

A bicomponent fluorinated polyurethane coating was obtained by crosslinking a bifunctional, OH terminated perfluoropolyether oligomer with a fluorinat ed polyisocyanate based on the isophorone diisocyanate (IPDT) cyclic-trimer . Three different tin containing catalysts (dibutyltin dilaurate (DBTDL), d ibutyltin dimercaptide (DBTDM), tin octoate (TO)) were evaluated during the crosslinking reaction through gel Lime measurements and DR spectroscopy at various temperatures from +15 to +45 degreesC. Both the methods showed a s ubstantial higher activity of the first two catalysts, tin octoate being al most ineffective (latent) at ambient temperature. The spectroscopic measure ments allowed the determination of apparent second-order kinetic constants (k) of the crosslinking reaction. The activation energies E-a in the temper ature range considered were obtained from the corresponding Arrhenius plot, showing a temperature dependence higher for DBTDM than DBTDL (8.5 vs. 7.0 kcal/mol). Finally, the conversion of the crosslinking reaction on the dry polymer film was estimated to be around 60-80% after only 20-25% for TO cat alyzed reactions. The formation 8 h at ambient temperature for DBTDM and DB TDL, but of a hard urethane phase having a glass transition temperature T-g higher than the crosslinking temperature was considered as the main limiti ng factor of the overall reaction rate.