C-methylols

Resoles. The advancement and cure of resole resins foUow reaction steps similar to those used for resin preparation the pH is 9 or higher and reaction temperature should not exceed 180°C. Methylol groups condense with other methylols to give dibenzyl ethers and react at the ortho and para positions on the phenol to give diphenyknethylenes. In addition, dibenzyl ethers eliminate formaldehyde to give diphenyknethanes. 

Dimers 15-19 represent the ji-5 bonding pattern. Upon thioacidolysis, the ben-zylic ether linkage of phenylcoumaran-type models is cleaved with concomitant thio-ethylation. The C. -methylol group of ji-5 structures is lost to an extent that depends on thioacidolysis duration. In contrast, the total amount oi 16+ 17 or 18 +19 is stable when this duration varies between 3 and 6 hours. Minor dimers of the ji-5 series are observed as dimers with shortened side chains, similar to dimer 15 or with rearranged side chains similar to monomers 4-5 (Figure 2.4). 

These compounds are listed under C-methylols because monomethylol nitro-propane and dimethylol nitropropane are the intermediates in the synthesis which react with morpholine to form the end products. 

Self-cross-linking Other C-methylol Ester interchange Amino groups... 

On the contrary, under oxidative conditions, the secondary l dKM l groi p formed by the partial oxidation of the methylene group of phenol-formaldehyde resin is likely to react with metl -lol group of polyesterimide. The schane of reaction m be shown as in (Scheme IV). The -CH2(ffl group of the polyesterimide may be either N- nethylol group of C-methylol group. 

A fiactionating column is lequked foi the removal of ammonia and recycle of ethylenediamine. The molten product (mp 133°C) is then mn into ice water to give a solution that is methylolated with 37% aqueous formaldehyde. 

Temperatures in excess of 140°C are required to complete the reaction and pressurized equipment is used for alcohols boiling below this temperature provision must be made for venting ammonia without loss of alcohol. The reaction is straightforward and, ia the case of the monomethyl ether of ethylene glycol [109-86-4] can be carried out at atmospheric pressure usiag stoichiometric quantities of urea and alcohol (45). Methylolation with aqueous formaldehyde is carried out at 70—90°C under alkaline conditions. The excess formaldehyde needed for complete dimethylolation remains ia the resia and prevents more extensive usage because of formaldehyde odor problems ia the mill. 

Formaldehyde may react with the active hydrogens on both the urea and amine groups and therefore the polymer is probably highly branched. The amount of formaldehyde (2—4 mol per 1 mol urea), the amount and kind of polyamine (10—15%), and resin concentration are variable and hundreds of patents have been issued throughout the world. Generally, the urea, formaldehyde, polyamine, and water react at 80—100°C. The reaction may be carried out in two steps with an initial methylolation at alkaline pH, followed by condensation to the desired degree at acidic pH, or the entire reaction may be carried out under acidic conditions (63). The product is generally a symp with 25—35% soHds and is stable for up to three months. 

In general their work indicates that at temperatures below 160°C cross-linking occurs by phenol methylol-phenol methylol and phenol methylol-phenol condensations, viz Figure 23.13. 

Reaction of melamine with neutralised formaldehyde at about 80-100°C leads to the production of mixture of water-soluble methylolmelamines. These hydroxymethyl derivatives can possess up to six methylol groups per molecule and include trimethylolmelamine and hexamethylolmelamine (Figure 24.8) The methylol content of the mixture will depend on the melamine formaldehyde ratio and on the reaction conditions. 

In a typical process a jacketed still fitted with a stirrer and reflux condenser in charged with 240 parts 37% w/w (40% w/v) formalin and the pH adjusted to 8.0-8.5 using sodium carbonate solution with the aid of a pH meter. One hundred and twenty six parts of melamine (to give a melamine formaldehyde ratio of 1 3) are charged into the still and the temperature raised to 85°C. The melamine goes into solution and forms methylol derivatives. For treatment of fabrics, paper and leather this product may be diluted and cooled for immediate use. It may also be spray dried to give a more stable product. Cooling the solution would yield crystalline trimethylolmelamine, which may be air dried but which is less soluble in water than the spray-dried product. 

Thiourea will react with neutralised formalin at 20-30°C to form methylol derivatives which are slowly deposited from solution. Heating of methylol thiourea aqueous solutions at about 60°C will cause the formation of resins, the reaction being accelerated by acidic conditions. As the resin average molecular weight increases with further reaction the resin becomes hydrophobic and separates from the aqueous phase on cooling. Further reaction leads to separation at reaction temperatures, in contrast to urea-formaldehyde resins, which can form homogeneous transparent gels in aqueous dispersion. 

The final phase of resole manufacture is known as the condensation stage (Scheme 3). This is the actual process by which molecular weight is developed and involves the combination of the hydroxymethyl phenol intermediates to form oligomers. It can be reasonably well separated from the resole methylolation reaction in practice by maintaining reaction temperatures below about 70°C. The activation energy for condensation is higher than that for methylolation. This is not to say that condensation does not occur at temperatures below 70°C. It simply means that the methylolation is much faster than condensation at this temperature. 

Furthermore, 70°C is a temperature that promotes the methylolation at a rate that is usually acceptable for manufacturing productivity. 

The observation of condensation products at 30°C may seem to contradict statements made earlier regarding our ability to separate the methylolation and condensation reactions by holding reaction temperatures below 70°C. Flowever, there is no conflict. The differences in the situations are primarily matters of absolute rate. The relative rates are still similar for methylolation and condensation. No... 

The activation data collected by Zavitsas et al. at 30 and 57°C was extrapolated to 70-90°C by Ferrero and Panetti and tested against experiment. The data fit well throughout the temperature range. Fig. 9 and Table 6 show these activation data for each species involved in the methylolation process. 

Scheme 10. Mechanislic possibililies for PF condensalion. Mechanism a involves an SN2-like attack of a phenolic ring on a methylol. This attack would be face-on. Such a mechanism is necessarily second-order. Mechanism b involves formation of a quinone methide intermediate and should be Hrst-order. The quinone methide should react with any nucleophile and should show ethers through both the phenolic and hydroxymethyl oxygens. Reaction c would not be likely in an alkaline solution and is probably illustrative of the mechanism for novolac condensation. The slow step should be formation of the benzyl carbocation. Therefore, this should be a first-order reaction also. Though carbocation formation responds to proton concentration, the effects of acidity will not usually be seen in the reaction kinetics in a given experiment because proton concentration will not vary.

The reaction rate increases when heated to temperatures up to 40°C. The amino derivatives can then be quaternized if desired. The N-methylol derivatives of polyacrylamide can be made cationic by heating with amines, or they can be made anionic by heating with aqueous bisulfite solution under basic conditions. 

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