Groups, epoxy

Ahyl alcohol undergoes reactions typical of saturated, aUphatic alcohols. Ahyl compounds derived from ahyl alcohol and used industriahy, are widely manufactured by these reactions. For example, reactions of ahyl alcohol with acid anhydrides, esters, and acid chlorides yield ahyl esters, such as diahyl phthalates and ahyl methacrylate reaction with chloroformate yields carbonates, such as diethylene glycol bis(ahyl carbonate) addition of ahyl alcohol to epoxy groups yields products used to produce ahyl glycidyl ether (33,34). 

Allyl Glycidyl Ether. This ether is used mainly as a raw material for silane coupling agents and epichlorohydrin mbber. Epichlorohydrin mbber is synthesized by polymerizing the epoxy group of epichlorohydrin, ethylene oxide, propylene oxide, and aHyl glycidyl ether, AGE, with an aluminum alkyl catalyst (36). This mbber has high cold-resistance. 

In the synthesis of AGE with an acid as the catalyst, aHyl alcohol is added to the epoxy group of epichlorohydrin, yielding 3-aHyloxy-l-chloro-2-propanol [4638-03-3], which then undergoes cyclization with alkaU to yield AGE. Catalysts such as H2SO4, SnCl, BE (C2H )20 (33), heteropolyacids, HQO, andy -CH CgH SO H (34) are used. 

Epoyy Resins. Titanates react with free hydroxy groups in epoxy resins or with the epoxy group itself ... 

Epoxy Resins. Epoxy resins (qv) are used to cross-link other resins with amine, hydroxyl, and carboxyHc acid (or anhydride) groups. The epoxy group, properly called an oxkane, is a cycHc three-membered ether group. By far the most widely used epoxy resins in coatings are bisphenol A (BPA) (4,4 -(l-methylethyHdene)bisphenol) [80-05-7] epoxy resins. 

In order to enhance the reactivity of the chlorine atom, a second reactive monomer can be adopted giving dual cure sites. According to the Hterature, the second monomer can contain carboxyl (22—24), cyanoalkyl (25), hydroxypropyl (26), or epoxy groups (27,28). 

The outstanding performance characteristics of the resins are conveyed by the bisphenol A moiety (toughness, rigidity, and elevated temperature performance), the ether linkages (chemical resistance), and the hydroxyl and epoxy groups (adhesive properties and formulation latitude, or reactivity with a wide variety of chemical curing agents) (see also Phenolic resins). 

The multiepoxy functionality of the epoxy novolaks (2.2 to >5 epoxy groups per molecule) (3) produce more tightly cross-linked cured systems having improved elevated temperature performance and chemical resistance than the difunctional bisphenol A-based resins. 

The functionaHty of the terminal epoxy groups approaches values greater than 1.9, but this is in large measure a function of controlling the foUowing side-reactions ... 

The epoxide resins (also widely known as epoxy resins and, occasionally, as ethoxyline resins) are characterised by the possession of more than one 1,2-epoxy group (I) per molecule. This group may lie within the body of the molecule but is usually terminal. 

Mol. ratio epichlorohydrin bis-phenol A Mol. ratio NaOHl epichlorohydrin Softening point rc) Molecular weight Epoxide equivalent Epoxy groups per molecule... 

The epoxide equivalent is a measure of the amount of epoxy groups. This is the weight of resin (in grammes) containing 1 gramme chemical equivalent epoxy. For a pure diglycidyl ether with two epoxy groups per molecule the epoxide... 

This ion may then open up a new epoxy group generating another ion which can in turn react with a further epoxy group. 

The overall reaction is complicated by the fact that the epoxy group, particularly when catalysed, will react with hydroxyl groups. Such groups may be present due to the following circumstances ... 

Reaction of the carboxylic group with the epoxy group (Figure 26.7). 

Etherification of the epoxy group by hydroxyl groups (Figure 26.8). 

Phthalic anhydride (Figure 26.10 I) is an important example of the first class of hardener. It has a molecular weight of 148 and about 0.6-0.9 equivalent is used per epoxy group. For the lower molecular weight bis-phenol resins this works out at about 35-45 phr. The hardener is usually added at elevated temperature of about 120-140°C. It will precipitate out below 60°C but will again dissolve on reheating. 

The number of epoxy groups per molecule will vary but for modified soya bean oils there are an average of about four whereas there are about six for epoxidised linseed oils. 

The low molecular weight polysulphides have found somewhat greater use. Of general structure HS—R—SH and with molecular weights of approximately 1000 they will react with the epoxy group to cause chain extension but not cross-linking. The normal hardeners must therefore be employed in the usual amounts (Figure 26.20). 

Note Trichothecenes and valepotriates only react when there is an epoxy group present in the molecule their detection limits are in the range 25—200 ng substance per chromatogram zone [1]. The detection limits for acetylene derivatives are 100— 800 ng substance per chromatogram zone, but not all give a positive reaction [8]. 

The physico-mechanical, thermal, and adhesion properties of the synthesized polyfunctional PSs are dependent on the nature of functional groups in the aromatic ring. In this case, the following are properties of the chlorohydrin and epoxy groups highest elasticity, resistance to strike, and adhesion properties with carboxyl and olefinics. Furthermore, the—CO—CH=CH-—COOH group was provided new properties such as the photosensitive capability. Functionalized PSs obtained are characterized by their high thermostability, adhesion, and photosensitivity. 

The isocyanate group is more reactive than the epoxy group in that it will react at room temperature with water and hydroxyl groups as well as with amine groups. However, the latter reaction is too fast to be practicable so the standard two-pack coatings are based on isocyanate and polyhydroxyl prepolymers such as hydroxyl terminated polyesters or polyethers as in the last example given in the section on epoxy resins. 

The polyaddition reaction in stoichiometric mixtures of glycidyl ethers and bisphenol A resulted in macromolecular chains. Although these chains lack any fixed order in space, their composition is remarkably regular since each epoxy group reacts with one phenol and each phenol group reacts with just one epoxy group (Fig. 2.1) Side reactions are much less favoured. The reaction is essentially complete. 

No epoxy groups were detectable in the cured polymer by infrared spectroscopy. 

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