Isocyanate cross-linkers

Figure 7. HPGPC chromatograms of four isocyanate cross-linkers...

Figure 8. HP GPC chromatograms of two isocyanate cross-linkers from different...

Figure 1. Typical melaminc-fonnaldehydc and isocyanate cross-linkers.

Otherwise a co-network would have been obtained. Thus PDMS network was formed starting from a,co-(3-hydroxypropyl)polydimethylsiloxane (diOH-PDMS oligomer) by DBTDL catalyzed addition between the hydroxy end groups and an pluri-isocyanate cross-linker (Scheme 2). No side reaction has been detected between these precursors. 

To the volumetric flask (5 mL) add the isocyanate cross-linker MBPI (5 mg) and make up the solution using dry dichloromethane (5 mL). 

Other water-soluble, blocked isocyanate cross-linkers have been prepared by reaction of diisocyanate with a,a-dimethylolpropionic acid followed by blocking with caprolactam and subsequent solubilization in water by means of a tertiary amine (81) or 2-ethylimidazole (82). 

Emulsion Polymer Isocyanate (EPI) adhesives are two-component adhesive systems consisting of water-based emulsions cured with an isocyanate cross-linker. The first EPI adhesives were developed in Japan in the early I970 s and this adhesive type has been extensively used in Japan since then [1-3]. 

Originally the adhesive system consisted of an aqueous poly(vinyl alcohol) solution with an isocyanate cross-linker. At this stage the common name was Aqueous Polymer Isocyanate (API) [3]. Further developments including use of different types of polymer emulsions, like poly(vinyl alcohol) (PVA), ethyl(vinyl acetate) (EVAc), styrene butadiene rubber (SBR) or acrylic-styrene (AcSt) emulsion, led to adhesives systems with improved performance, hence today the common abbreviation is EPI [4, 8]. The isocyanate cross-linking agent has also been further developed to improve the compatibility and the reactivity with the water-based component, thus several different types are now available for use in EPI adhesives. 

In order to complete coverage of powder coatings, we must mention here the urethane cross-linked powders. In these cases we have hydroxy functional resins, which may be either polyester or acrylic. These are cross-linked by blocked isocyanate cross-linkers, principally those blocked with e-caprolactam as will be described in the next chapter. 

This resin will be partly neutralized with acetic or lactic acid, and co-emulsified with a blocked isocyanate cross-linker (p. 225). This type of resin is now the standard protective primer coating on the majority of the world s motor cars. Pigmentation will include anti-corrosive pigments. 

Figure 9 Dual-curing of an hydroxy-functionalised polyurethane-acrylate associated to an isocyanate cross-linker (/ = 500 mW cm ).

The solvent-borne clearcoat is spray-applied over the basecoat at a dry film thickness of 1.8 to 2.0 mils. The clearcoat, responsible for UV protection, chemical resistance, chip resistance, and so on, is most often composed of a hydroxy functional acrylic binder together with a melamine or an isocyanate cross-linker. Ultraviolet light absorbers and hindered amine light stabilizers also are added to achieve better free-radical oxidative degrada-... 

The choice of vulcanizing agents has been much the same for the past 150 years with the exception of the use of an isocyanate cross-linker added during the last 50-60 years. Elemental sulfur (brown factice), sulfur chloride (white factice), hydrogen sulfide (light yeUow/translucent factice), isocyanate, and peroxide (very white/hard/translucent factice) comprise the main types employed for vulcanizing vegetable oils. 

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