Self-Healing Polyurethane Elastomers

Patent Title: POLYURETHANE

 Number/Link: W02016185172

Applicant/Assignee: Croda

Publication date: 24-11-2016

Gist”: PU from polyols which contain both a fatty dimer residue and an H-bonding group, show self-healing properties

Why it is interesting: Polyurethane elastomers with ‘intrinsic’ self-healing properties (i.e. without the need for external chemicals like encapsulated monomers) can be prepared by reacting isocyanates with polyols that have at least one urethane, amide or carbonate group and at least one fatty dimer residue. It is theorized that the fatty dimer allows the soft-phase of the polymer to flow and H-bonds to form, thus restoring most of the properties after damage.  In the examples polyols with internal urethane groups were prepared by reacting C36 dimer diol with HDI, which were then reacted with MDI and BDO. Samples of the resulting elastomers were cut in half, and manually stuck together again under mild heating (60°C), thus recovering most of their tensile and elongation properties.

A dimer diol

A dimer diol

Classic PU Patent of the Month: Microencapsulation (1963)

Patent Title: ENCAPSULATION BY INTERFACIAL POLYCONDENSATION

 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-Healing Polyurethane Coatings

Patent Title: Self-Repairing Polyurethane Networks

 Number/Link: US20160289495

Applicant/Assignee: Clemson University

Publication date: 6-10-2016

Gist”: Polyurethane networks with alkylated polysaccharide moiety show self-healing properties

Why it is interesting: Chitosan (pref.) is alkylated by reacting with dodecylaldehyde (in solvent) and reducing the resulting imine with sodium cyanoborohydride. The alkylated chitosan is then reacted with isocyanate and polyol.  When used as coating, the material is claimed to show self-healing properties when irradiated with UV light. Modifying the composition by incorporation of catechol, or by changing the saccharide allows for materials which ‘heal’ when exposed to ferric ions or carbon dioxide. No explanation for this behaviour is given and it is not immediately clear to me why this should work.

Self-healing network according to the invention. The isocyanate used was (E)-3,5-bis(6-isocyanatohexyl)- 6-( ( 6-isocyanatohexyl)imino )-1,3,5-oxadiazinane-2, 4-dione.

Self-healing network according to the invention. The isocyanate used was (E)-3,5-bis(6-isocyanatohexyl)-6-( ( 6-isocyanatohexyl)imino )-1,3,5-oxadiazinane-2,4-dione. ALK= alkyl, POL=polyol.

 

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