CROSS-LINKING OF WATERBORNE POLYURETHANE DISPERSIONS

A hydroxyl/carboxyl functional low molecular weight polyurethane dispersion was prepared by a nonisocyanate process. It was compared to a conventional high molecular weight polyurethane dispersion in films cured with melamine-formaldehyde resins. Stress-strain studies and solvent swelling experiments were used to characterize network formation and determine crosslink density. The morphology of the films prepared from the two types of polyurethanes were different, and coatings performance advantages were found with the low molecular weight polyurethane dispersion. Surface analysis by FTIR ATR indicates a more uniform distribution of melamine crosslinker in the cured low molecular weight polyurethane coating.