Patent Title: Self-Crosslinkable Polymer and Aqueous Dispersion Comprising Particles of the Same

 Number/Link: US2016/0159959

Applicant/Assignee: Valspar Sourcing

Publication date: 9-06-2016

“Gist”: Aqueous dispersion of polyurethane having both azide and carbonyl groups in the backbone

Why it is interesting: Properties of water-based PU coatings can often be improved by incorporating olefinically unsaturated groups in the polymer which can be crosslinked using radiation. According to this invention a self-crosslinking (i.e. without the need for radiation) aqueous PU coating composition can be made by incorporating both azide- and carbonyl groups into the PU backbone. When the water evaporates and the film forms these groups will react forming a hydrazone-type bond. The self-crosslinkabe polymer can be prepared by first making an NCO-ended prepolymer containing a reactive double bond, by (e.g.) reacting some of the NCO groups with hydroxyethylmethacrylate (HEMA). This prepolymer is then dispersed in water together with hydrazine and and acrylate like MMA or BA. The hydrazine will react with the NCO groups, introducing azide groups into the backbone.  The acrylate and the prepolymer are then suspension polymerized using an initiator.  The PU backbone can (optionally) contain a water dispersible group – e.g. by incorporating dimethylolpropanoic acid. The self-crosslinkable polymer is said to be especially useful for use in wood coating compositions.

Hydrazine