Epoxy Resin of Olefin Compounds

The epoxy resin of this class are the products f epoxidation effected by means of an oxygen-donating substance, referred to at the beginning of this section as the second method of producing epoxy resins.

These resins will be discussed only briefly because, although they have created considerable interest, they can not yet be said to have assumed importance as adhesives.

Epoxides of this class comprise both cycloaliphatic and aliphatic structures, examples are dicyclopentodiene dioxide (mp. 184oC), vinyl cyclohexene dioxide (a liquid), structures containing cyclohexene oxide rings (usually liquids), and epoxidised butadiene resins (usually liquids). In their development the Union Carbide Corporation of USA, Ciba of Switzerland and the Food Machinery Company of USA have been prominent.

The epoxidation process involves the use of an olefinic or polyolefinic compound and a peracid or other oxidizing substance such as hydrogen peroxide or molecular oxygen; even air has been used. Commercially, however, peracetic acid (substantially free of impurities) is commonly used. Included in the large number of compounds to which the method can be applied are the products of the Diels Alder reaction between a conjugated diene, in particular butadiene, and a dienophile to form a cyclohexene, the cyclohexene molecules being subsequently joined to form a bicyclic olefine which can be epoxidesed.

Batzer and NIkles, in considering types of epoxide and epoxidation methods, have especially discussed the reactions of the cycloaliphatic epoxides, and reviewed them in relation to the glycidyl ether of bisphenol A.

The work on cyclohexene oxide derivatives has led to the development of the liquid diepoxide, 3,4 epoxy-6-methylcyclohexymethyl 3,4-epoxy-6-methylcyclohexane caboxylte, made from butadiene and croton aldehyde, whose structure (XVI) is simpler than its name and is shown below.

Another cyclohexene oxide derivative is the epoxidised acetal (XVII) of tetrahydrobenzaldehyde and 1,1-bis(hydroxymethy) cyclohex-3-ene (Araldite) whose structure is:

Epoxyalkyl Ester Adhesives

Glycidyl compounds can be made by the reaction of epichlorohydrin with a substance other than an amino or hydroxyl compound, and the products of reaction with polycarboxylic acids or anhydrides known as epoxyalkyl ester are of some interest. These resins, wherein the important functional groups are epoxide, are quite unlike the polyester referred to.

In the development of the epoxyalkyl ester adhesives, Henkel and Cie of Germany have been prominent. Epoxyalkyl esters can be prepared by reacting a halide of a polybasic aromatic carboxylic acid with an epoxide compound containing a hydroxyl group such as glycidol, also by reacting a salt of such an acid, or the acid or anhydride itself in the presence of a catalyst with epichlorohydrin.

Adhesives based on epoxyalkyl esters can be hardened with aliphatic polyamine, or with an acid or acid anhydride. They show good adhesion to a wide veriety of materials including glass, marble, porcelain, rubber and metals, and they are resistant to hot and cold water. An example of the metal to metal strength of both a hot-cured and a room temperature cured epoxyalkyl ester is shown in the figure,.