Self-Crosslinkable Polyurethane

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

Hydrazine

 

Highly Stable Isocyanate Dispersions

Title: STORAGE-STABLE HYDROPHILIC POLYISOCYANATES

 Number/Link: WO2014/053269   (German)

Applicant/Assignee: Evonik

Publication date: 10-04-2014

Gist”: A uretdion-containing isocyanate prepolymer is reacted with a neutralized aminealkylsulfonic acid to produce a novel hydrophilic (latent) isocyanate which can be used in stable aqueous dispersions.

Why it is interesting: Aqueous dispersions of isocyanates are useful in many applications as adhesives, binders, crosslinkers etc, but usually suffer from a relatively short shelf life.  Dispersions prepared according to the current invention supposedly lose less than 30% of their initial NCO value after 12 weeks storage at 50°C. In an example an aceton-solution of  an IPDI-uretdion prepolymer with an isocyanate content of 1.5% is reacted with the sodium salt of an aminealkylsulfonate in water to an NCO value of 0.1%. After removal of the aceton the resulting dispersion had a latent isocyanate content of 4.5%

Dimerization of isocyanate to uretdion.

Reversible dimerization of isocyanate to uretdion.

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