Cresol-blocked

Mondur SH, thought to be a cresol blocked TDI trimer (Mobay)... 

Commercially available blocked isocyanates include Hylene MP or 4715 from Du Pont (now withdrawn), which is phenol-blocked MDI (Du Pont International S.A., Geneva, Switzerland) Mondur S, a phenol-blocked TDI adduct, Mondur SH, a cresol-blocked TDI trimer,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 ... 

XXIII) Mondur SH—a cresol-blocked TDI trimer, presumably... 

Significant quantities of the diphenoquinone are also produced if the ortho substituents are methoxy groups (36). Phenols with less than two ortho substituents produce branched and colored products from the reactions that occur at the open ortho sites. It is possible to minimize such side reactions in the case of o-cresol oxidation by using a bulky ligand on the copper catalyst to block the open ortho position (38). 

In addition to the above possible mechanisms the possibility of reaction at w-positions should not be excluded. For example, it has been shown by Koebner that o- and p-cresols, ostensibly difunctional, can, under certain conditions, react with formaldehyde to give insoluble and infusible resins. Furthermore, Megson has shown that 2,4,6-trimethylphenol, in which the two ortho- and the one para-positions are blocked, can condense with formaldehyde under strongly acidic conditions. It is of interest to note that Redfam produced an infusible resin from 3,4,5,-trimethylphenol under alkaline conditions. Here the two m- and the p-positions were blocked and this experimental observation provides supplementary evidence that additional functionalities are developed during reaction, for example in the formation of quinone methides. 

To a 50-mL straight-wall three-necked flask (Fig. 3.18b) equipped with a magnetic stirrer, nitrogen inlet/outlet, and condenser unit in a heating block are added 11.29 g of nylon salt and 0.093 g of hexamethylene diamine (2 mol % excess). This mixture is reacted for 2 h at 210° C and 3 h at 270°C. The resultant polymer is colorless and transparent and has a r/rei of 2.54 (1% solution in m-cresol, 25°C). 

At the end of the polymerization reaction, octadecyl 3-(3,5-di-ferf-butyl-4-hydroxyl)propionate, and in addition 2,5-di-ferf-but-yl-p-cresol are added as antioxidants in order to protect the product during solvent elimination, drying and storage. Morphologies, such as rods, points or capsules can be obtained by tailoring the polydispersity of the poly(styrene) block (10). 

Further insight came from our study of other aromatic substitution reactions. When we blocked the para position of anisole in compound 65, we saw that ortho chlorination was blocked by binding with a-cyclodextrin, so the only reaction was from the substrate that was in free solution, not that which was bound. However, with p-cresol (66) there was still, of course, ortho chlorination but now it was catalyzed by the a-cyclodextrin. When p-cresol binds to the cyclodextrin, the polar phenol or phenoxide group will be out of the cavity, bringing the ortho positions within reach of the cyclo-... 

Figure 2.2 Block diagram for p-cresol production (conventional) plant.

Figure 3.2 Block diagram showing enrichment of lean p-cresol to pure p-cresoL...

---