Ketoxime-blocked

Blocked isocyanates are also nsed as cross-linking agents for powder coatings. Becanse of its high melting point, caprolactam blocked, l-(isocyanatomethyl)-5-isocyanato-l,3,3-trimethyl-cyclohexane (IPDI) is commonly used. Especially suited for this application are isocyanurate trimers. Despite catalysis with DBTDL, caprolactam-blocked isocyanates require a cure temperature of 180-200 °C. To achieve a lower cure temperature of about 140 °C, ketoxime-blocked isocyanates are used.i°°... 

The tough and weatherable epoxy-acrylic graft copolymers made by Oriel et al. (20) that were cited earlier were also made from methyl ethyl ketoxime blocked lEM. 

Recently Saunders (39) conducted a detailed study of emulsion latices made from methyl ethyl ketoxime-blocked lEM (lEM-MEKO). Compositions investigated were styrene/-butyl acrylate/IEM-MEKO, styrene/butyl aerylate/IEM-MEKO latex formulated with active hydrogen compounds and styrene/butyl acrylate/IEM-MEKO copolymerized with vinyl acids or hydroxy monomers. The effect of urethane catalysts on the deblocking/curing reaction was also studied. 

The miscibility of FBZ resins with the main classes of conventional polyisocyanate cross-linkers was also tested, and it was found that they can be blended and formulated with some blocked NCO hardeners as the ketoxime-blocked isocyanurates, in order to obtain monocomponent or one pack (IK) high-solid polyurethane coatings " as shown in Scheme 2. Such formulations are... 

Commercially available blocked isocyanates include Hylene MP or 4715 from Du Pont (now withdrawn), which is phenol-blocked MDI (Du Pont International S.A., Geneva, Switzerland) Mondur S, a phenol-blocked TDI adduct, Mondur SH, a cresol-blocked TDI trimer, and Experimental E-320-blocked isocyanate, a ketoxime-blocked tetraisocyanate, all from Mobay (Pittsburgh, Pennsylvania, USA) and Isonate 123P, which is s-caprolactam-blocked PAPI, from the Upjohn Company (Dow Chemical Europe, Horgen, Switzerland). These are shown in Fig. 8.9. Uniroyal also market a product. 

Conunercially available blocked isocyanates have included Hylene MP from duPont (XXI) " which is phenol-blocked MDI Mon-dur S (XXII), a phenol-blocked TDI adduct Mondur SH (XXIII), a cresol-blocked TDI tiimer and Experimental E-320 blocked isocyanate (XXIV), a ketoxime-blocked tetraisocyanate, all from Mobay and Isonate 123P (XXV)" which is -caprolactam-blocked PAPI from the Upjohn Company. The Ashland Chemical Company has marketed a conuner-cial chemical class called aminimides which act as isocyanate precursors, eliminating the problem of by-product phenol from the use of phenol-blocked isocyanates.Their chemistry relevant to this use, is as follows ... 

XXIV) Experimental E-320 Blocked Isocyanate—a ketoxime-blocked tetraisncyanatp 36.38.39... 

Extension of the reaction to diacetylene might clear the way to the ethynylpyrroles 114, promising monomers for conducting polymers and building blocks for the synthesis of new heterocycles. It turned out (76ZOR905) that, in an aqueous DMSO in the presence of catalytical amounts of KOH, diacetylene indeed added exothermically to ketoximes to form O-1 -butene-3-viny(ketoximes (113) (Scheme 54). 

Xiao et al. (1995) developed a one-pack cross-linkable water-borne coating from anionic-blocked isocyanate-containing urethane prepolymers. The anionic-blocked urethane dispersions were prepared from poly(oxypropylene) glycol, polyarylpolyisocyanate, dimethylolpropionic acid and methylethyl ketoxime. The coatings based on these dispersions were reported to show good mechanical properties and chemical resistance. 

Blocked isocyanates are being used in coil coatings, depending on cure temperature, and end uses aliphatic or aromatic isocyanates blocked with 3,5-dimethylpyrazole, methylethyl ketoxime or caprolactam are being employed. 

The presence of an a-methylene group permits the enoli-zation of the hit molecule, this tautomery is blocked through the insertion of a spiro cyclopropyl ring (Figure 19.13). Result of a formal oxidation yields the secondary alcohol. Double bond possibilities are a-methylene (X = CH2), the diketone (X = O) and the corresponding ketoxime (X = N-OH). 

Similarly, an aqueous treatment for wool uses an isocyanate blocked with a bisulfite. In this case, the by-product bisulfite salt can be removed, and possibly recycled, by washing the fabric with water at the end. The dissociation temperature decreases in the following order alcohol > lactam > phenol > ketoxime > active methylene compound. e-Caprolactam is a typical lactam, ethyl acetoacetate a typical active methylene compound. This thermal reversibility has been used to prepare a polyurethane from 1,4-butanediol, 4,4 -diphenyldiiso-cyanate, and 4,4 -isopropylidenediphenol (bisphenol A) (2.30) that can be recycled just by remolding.76... 

Nitration studies on a series of 3-methyl- and 3-ethylindoxazenes have been recorded.12 3-Methyl- and 3-ethylindoxazene yield a mixture of the 5-nitro and 5,7-dinitro derivatives. If the 5-position is blocked (e.g., by chloro or alkyl groups) then, surprisingly, nitration takes place at the 4-position. As expected, the 7-chloro-3-alkyl and the 3,7-dialkyl derivatives are nitrated exclusively at the 5-position, whereas the 3,6-dialkyl and 3-alkyl-6-chloro derivatives yield a mixture of the 5-nitro and 5,7-dinitro compounds. The structures of the nitro compounds were confirmed by H-NMR spectroscopy and, in some instances by synthesis from the nitro-substituted ketoxime acetates (see Section II,A,2). 

TetramethyM, 4-bis-(N,N-dimethylamino) disilethylene blocking agent, isocyanate Caprolactam Diethyl malonate Methyl ethyl ketoxime Phenol... 

Blocked isocyanate coating in which the isocyanate has been reacted with a phenol or ketoxime. When the blocked isocyanate is heated, the original isocyanate is liberated and reacts with a polyol present in the formulation to give a very hard polyurethane film. Phenolic vapours, together with traces of the parent isocyanate, are driven off with solvent vapours. 

Blocked isocyanates can be used in the cross-linking of hydroxyl group containing polymers in the formulation of powder coatings. Blocking agents include phenol, caprolactam, ketoximes, and 3,5-dimethylpyrazole. The latter has the lowest dissociation temperature (22). Currently, virtually all automobiles produced use a blocked isocyanate in the formulation of cationic electrodeposition coatings (23). The [2 -i- 2] cycloadduct derived from MDI and diarylketenes is used as an initiator in the nylon RIM process (24). 

Steric crowding on either oxime or isocyanate enhances the dissociation rates. Isocyanates blocked with diisopropyl and diisohutyl ketoximes dissociate faster than the same isocyanates blocked with MEKO (15). Oxime blocked TMXDI dissociates faster than other less sterically crowded aliphatic isocyanates and with comparable rates to aromatic isocyanates. Blocked TMI cross-linkers can be synthesized by first copol5merizing the TMI with acrylate esters, and then reacting the polyfimctional acrylate with an oxime such as MEKO. Alternatively, one can react TMI with the oxime and then copolymerize the blocked monomer with acrylate esters (16). 

One-Component Silicones. The liquid silicone prepolymers used in one-component sealants are usually methyl-substituted polysiloxanes having more than two blocked, hydrolyzable end groups. These groups may be acetoxy, ketoxime, alkylamino, or benzamido. When the composition is extruded into a joint... 

For instance, blocked polyisocyanates based on aromatic polyisocyanates dissociate at lower temperatures than those based on aliphatic ones. Generally, the dissociation temperatures of blocked polyisocyanates based on commercially utilised blocking agents decrease in the order alcohols > s-caprolactam > phenols > methyl ethyl ketoxime > active methylene compounds. 

Both aliphatic and aromatic isocyanates can be blocked by a variety of blocking agents. These include alcohols, phenols, oximes, lactams, j8-dicarbonyl compounds, bisulfite addition compounds, hydroxylamines and esters of p-hydroxybenzoic acid and salicylic acid. Perhaps the most widely used blocking agents at present are phenol, branched alcohols, 2-butanone oxime (methyl ethyl ketoxime) and 8-caprolactam. The use of blocked isocyanates in PU coatings has been comprehensively reviewed. ... 

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