Classic PU Patent of the Month: Microencapsulation (1963)


 Number/Link:  US3577515

Applicant/Assignee: Pennwalt Corp.

Publication date: 4-05-1971

Gist”: Interfacial polycondensation on the surface of emulsified droplets.

Why it is interesting: Micro-sized droplets are encapsulated with a polymeric film or ‘skin’ formed by an interfacial polycondensation reaction. The idea is both very clever and simple: one reaction component is dissolved in a liquid which is then dispersed in another -immiscible- liquid. The second reaction component is then added to the continuous phase resulting in a polycondensation reaction at the surface of the droplets, encapsulating these with a polymeric film. For example a solution of a polyisocyanates in an organic solvent can be dispersed in water (to a desired droplet size) after which a water soluble diol or diamine is added resulting in a polyurethane or polyurea film encapsulating the solvent droplets. Microcapsules are now common and used in may applications like cosmetics, phase change materials, e-paper, self-healing coatings etc.

Figure 1 illustrating the process

Figure illustrating the process


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.




Melt-Dispersed Polymer Polyols


 Number/Link: WO2015/165761  (German)

Applicant/Assignee: BASF

Publication date: 5-11-2015

Gist”: Polymer polyols are prepared by melt-dispersing SAN into a carrier polyol using a specific stabilizer

Why it is interesting: Polymer polyols, or ‘graft polyols’, contain finely dispersed polymeric particles and are especially useful for the production of flexible polyurethane foams.  Usually polymer polyols are produced by in-situ polymerization of styrene-acrylonitrile (SAN)- or polyurea particles in a carrier polyol. In this invention, polymer polyols are prepared by dispersing molten SAN into a carrier polyol using shear mixing and a specific stabilizer.  The stabilizer is a (preferably) comb-shaped polyol-SAN copolymer, and is described in another BASF application: WO2015/165878. The polymer polyols are said to have a fine and uniform particle size distribution, a low viscosity and a high stability against segregation.



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