Unsubstituted heat-reactive phenolic reactivity

Unsubstituted and Heat Reactive. The first class, the unsubstituted, heat-reactive resins, are made by using phenol, cresols, and xylenols. They are multifunctional and thus can be cross-linked to form films. They are soluble in alcohols, ketones, esters, and glycol ethers and insoluble in aromatic and aliphatic hydrocarbons. They will tolerate some water in their solvents and, in some cases, are completely water soluble. They are compatible with polar resins such as amino resins, epoxies, polyamides, and poly(vinyl butyral), though compatibility on curing is dependent on reaction between the two resins. Less polar resins such as alkyds and drying oils are incompatible. 

Unsubstituted, heat-reactive phenolic resins are commercially available as 100% viscous liquids, as water and alcohol solutions, and as solid resins. The viscous liquids are mixtures of monomers and dimers of varying raethylolation. The water solutions contain resins of monomers and dimers with the highest degree of raethylolation. Alcohol solutions contain resins that are higher in molecular weight and are too reactive to isolate as solids. 

Waterborne Phenolic Resins. In addition to the unsubstituted, heat-reactive, water-soluble resins mentioned earlier, recent years have... 

Aqueous dispersions are alternatives to solutions of Hquid and soHd resins. They are usuaUy offered in 50% soHds and may contain thickeners and cosolvents as stabilizers and to promote coalescence. Both heat-reactive (resole) and nonheat-reactive (novolak) systems exist that contain unsubstituted or substituted phenols or mixtures. A related technology produces large, stable particles that can be isolated as discrete particles (44). In aqueous dispersion, the resin stmcture is designed to produce a hydrophobic polymer, which is stabilized in water by an interfacial agent. 

Raw Materials Base-Catalyzed Reactions Acid-Catalyzed Reactions Classification of Phenolic Resins Unsubstituted and Heat Reactive Unsubstituted and Nonheat Reactive Substituted and Heat Reactive Substituted and Nonheat Reactive Applications... 

Phenolic resins can be divided between heat-reactive and nonheat-reactive resins and between resins made by using unsubstituted or substituted phenols. A review of the four resulting classifications follows. 

Substituted and Heat Reactive. The third class, substituted and heat-reactive resins, are made by using para-substituted phenols where the substituent is a four-carbon or higher group such as tert-butyl, tert-octyl, and phenyl. Small amounts of ortho-substituted phenols and unsubstituted phenols are sometimes coreacted but, in general, the functionality is 2, and only linear molecules are formed. They are brittle solids that do not form films. The substituent makes the resins less polar and hence they are soluble in ketones, esters, and aromatic hydrocarbons, with limited solubility in alcohols and aliphatic hydrocarbons. The phenolic resins based on longer chain aliphatic phenols are more compatible with drying oils, alkyds, and rubbers. 

Unsubstituted and heat-reactive phenolic resins are extensively used as interior coatings for food cans because they provide odourless, tasteless, nontoxic, sterilizable and chemically resistant films. Due to high chemical-resistance properties, these resins are also used to protect oil-well drill-pipes, to protect the back of copper printing-plates and for lining solvent drums. 

The solubility of phenolic resins in different coating formulations is, however, affected by the type and chain length of substituent groups in the phenols. Depending on whether substituted or unsubstituted phenols are used, the phenolic resins can be further classified into two more groups of heat- and nonheat-reactive resins, having different applications. 

Unsubstituted and nonheat-reactive phenolic resins are used to a very limited extent due to their nonfilm-forming character. These resins are generally used as hardeners with epoxy resins to produce thermoset systems with high-quality engineering plastic properties. The base-catalyzed curing produces a crosslinked polyether structure, as shown in reaction (30), which is resistant to chemicals and heat and shows good barrier properties against moisture vapour. 

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