Epoxies, bisphenol A-epichlorhydrin

Reaction between a bisphenol A-epichlorhydrin epoxy resin and a polyfunctional amine thus results in a cross-linked polymeric structure. The process is illustrated by the reaction with triethylenetetramine (which has six reactive hydrogen atoms) ... 

As indicated in Section 16.3.2, conventional bisphenol A-epichlorhydrin epoxy resins are prepared by using an excess of epichlorhydrin they are polymers of low molecular weight (Mn seldom exceeding 4000) which are terminated by... 

Whilst the straight bisphenol A-epichlorhydrin epoxies described above have found widespread use in such applications as adhesives, castings, encapsulations, composites and laminates they are used to a relatively small extent in surface coatings. In this important field, mainly modified bisphenol A-epichlorhydrin epoxies are used. Two principal types of modification are commercially practised, namely combination with other resins and esterification. 

Bisphenol A is used with epichlorhydrin for the synthesis of epoxy resins bisphenol-A type. It leads to bisphenol-A diglycidyl ether, which is the monomer of bisphenol-A based epoxy resins. Reports of bisphenol-A sensitization, particularly in workers at epoxy resin plants, are controversial. Bisphenol-A was also reported as an allergen in fiberglass, semisynthetic waxes, footwear and dental materials. 

Evidence for this scheme is that chemically-bound nitrogen is found in the final product the rate of reaction is increased by the presence of phenols and anhydrous non-phenolic tertiary amines are not effective curing agents. Since bisphenol A-epichlorhydrin resins have epoxy groups at each end of the polymer the above scheme results in the formation of a cross-linked polymeric structure. 

Epoxy resin based on bisphenol-A-epichlorhydrin 4.32) is susceptible to photodegradation when exposed to prolonged UV radiation [675 814 1174 1340, 1691, 1698, 2109]. 

Bisphenol A-epichlorhydrin resins may be blended with a variety of other resins which contain reactive groups. On curing, interaction occurs to give a cross-linked copolymer which exhibits characteristics of the two straight resins. Examples of resins used in conjunction with epoxy resins are ... 

Epoxy Prepolymers. These prepolymers are commonly formed from Bisphenol A and epichlorhydrin (Figure 4). A variety of other materials are also employed, but to a lesser extent. The lowest member of the series might well be considered structoterminal, while all the others must be considered as structopendant prepolymers. Molecular weights range from a few hundred to about 4000 for commonly used industrial epoxy prepolymers. Most common cross-linking agents are amines and anhydrides however, epoxies may also be combined with a variety of other prepolymer systems (25). 

Epoxy resins derived from bisphenol A and epichlorhydrin show marked resistance to radiation if they are cured with aromatic agents. 

Epichlorhydrin is capable of reacting with hydroxyl groups, with the elimination of hydro-chlorie aeid. The most widely used epoxy resins are the family of products produced by the reaction between epiehlorhydrin and bisphenol A. 

For the less critical applications, standard (epichlorhydrin/bisphenol A) epoxy resins retain their physical properties well, but are particularly subject to the adverse effects of UV radiation on their appearance. This causes rapid yellowing and chalking due to their aromatic structure and UV agents are ineffective. Therefore, aU mouldings made with these resins which are to be subjected to extended outdoor exposure will benefit from protection by surface coating or shading. 

The most widely used epoxy resins are reaction products of either bisphenol A or a novolac phenolic resin with epichlorhydrin. When used to manufacture corrosion-resistant structures for use in the chemical process industry, epoxy resins are generally hardened with either aromatic or cycloaliphatic amines. The hardeners for epoxy resins are, with few exceptions, added at levels varying from 20phr (parts per hundred resin) to lOOphr. This means that the hardener is actually quite a high proportion of the matrix resin and has quite a profound effect on the mechanical and corrosion properties of the cured resin. Thus the selection of the most suitable hardener is critical to the eventual success of the application. Epoxy resins have viscosities of several thousand mPas at room temperature, which makes it much more difficult to wet out glass fibre efficiently with them than with polyesters. Wet-out therefore involves heating the resin formulation to between 40°C and 60°C to reduce the viscosity to less than 1000 mPas. 

Epoxy resins are generally made from epichlorhydrin (ECH) and diphenylolpropane (DPP), also known as bisphenol-A (BPA) ... 

Table 13.3 Typical properties of selected epoxy resins based on bisphenol-A and epichlorhydrin...

Fig. 14.1 Preparation of epoxy resin from epichlorhydrin and bisphenol A.

Jolanki R, Kanerva L, Estlander T (1995) Occupational allergic contact dermatitis caused by epoxy diacrylate in ultraviolet-light-cured paint, and bisphenol A in dental composite resin. Contact Dermatitis 33 94-99 Van Jost T, Roesyanto ID, Satyawan I (1990) Occupational sensitization to epichlorhydrin (ECH) and bisphenol-A during the manufacture of epoxy resin. Contact Dermatitis 22 125-126... 

Epoxy resins of the bisphenol A type are synthesized from bisphenol A and epichlorhydrin. Hardeners, such as amines (ethylenediamine, diethylenetriamine, triethylenetetramine, isophoronediamine, triethy-lenetriamine and 4,4 -diaminophenylmethane) or acid anhydrides (phthalic anhydride) are added. Reactive diluents may be added, such as allyl glycidyl ether, butanediol diglycidyl ether, -butyl glycidyl ether, o-cresyl glycidyl ether, hexanediol diglycidyl ether. 

The most common epoxy resins are the reaction products of bisphenol A with excess epichlorhydrin and have the structure shown in Structure 9.5. Because the simple diepoxide... 

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