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Crosslinking Behavior of One Component Polyurethane Coatings based on Malonate Blocked Polyisocyanates: the Effect of the Malonate Structure and Optimization of the NCO:OH Ratio

Greszta-Franz D., Itter U.

Farby i Lakiery

2012

nr 6

3--8

The effects of the ratio of the hardener to binder on the onset of the cure, glass transition temperature and the crosslink density of one-component polyurethane coatings based on diethyl malonate blocked polyisocyanates was investigated using dynamical mechanical analysis. The crosslinking density of the cured films attained its maximum at blocked NCO:OH ratio of ca. 0.7, which is below the value commonly used in formulations and indicates that also the second ester group of diethyl malonate must be involved in the crosslinking. Furthermore, the crosslinking behavior of polyisocyanates blocked with different malonates (dimethyl; diethyl; diisopropyl; di-tert-butyl) and with a malonate substituted at the central carbon atom (dimethyl ethylmalonate) was examined as well.