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

Classic PU Patent of the Month: ICI’s Perfect Elastomer (1995)


 Number/Link: WO 97/21750

Applicant/Assignee: ICI

Publication date: 19-06-1997

Gist”: A polar polyether softblock and highly symmertrical hardblock results in a near-perfect polymer morphology.

Why it is interesting: ICI’s “perfect PU elastomer” is accomplished by reacting a polar, low-reactive polyether triol (75% EO random, 42 OHv) and a ‘stacking’ chain extender (MEG) with a symmetrical diisocyanate (4,4′ MDI).  Some water can be added to a density of about 400 kg/m³. This combination results in a remarkable polymer morphology with a ‘nano’ phase-separated hard domain and a very ‘clean’ soft phase, resulting in a very high (>1) and symmetrical damping peak (tan δ) and an incredibly flat storage modulus (E’) up to about 200°C.  Damping at positive temperatures  is virtually zero, resulting in a very high resilience.  The patent actually claims the shape of the DMTA trace rather than the composition of the polymer.
The elastomer is not completely “perfect” in that it has relatively low mechanical properties, such that it is perferably used in a structural- or fiber/particle reinforced composite.

1Hz DMTA trace of ICI's "perfect elastomer".

1Hz DMTA trace of ICI’s “perfect elastomer”.

Classic PU Patent of the Month: ICI on “High EO – Pure MDI” Flexible Foams (1991)

Patent Title: Polyurethane Foams

 Number/Link: EP0547765

Applicant/Assignee: ICI

Publication date: 23-06-1993

Gist”: Flexible foams can be based on 4,4’MDI if the polyol contains 50 to 85% EO

Why it is interesting: The first flexible PU foams were all based on toluene diisocyanate and so-called “conventional polyols” (i.e. almost all-propylene oxide polyols). Attempts to replace TDI by the only other commercially viable diisocyanate (4,4′ MDI) failed because of premature phase separation of the highly symmetrical polyurea ‘hard block’, resulting in unstable foaming. The problem was eventually solved by using prepolymers and polymeric MDI, as mentioned before.  More than 10 years later it was shown that it is possible to make flexible foams with 4,4′-MDI if the polyol is polar enough to prevent early phase separation.  This was established by using polyols with high ethylene oxide content. The resulting foams have superior comfort and durability properties compared to both TDI and MDI flexible foams.



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