23 сентября, 2015 
Malyar Examples of the resin components of expoxies are listed in Table 1. Several chemical substances can be used as hardeners for epoxies [5,6]. The two main groups of crosslinking agents used in industry are two or more functionalized amines and anhydrides of carboxylic acids. Cross-linking with amines is possible at room temperature as well as at elevated temperatures, depending on the chemical structure of the amines (Table 2). Anhydrides of carboxylic acids react at elevated temperatures only.
The cross-linking of epoxies by amines follows the addition of a primary amine with two epoxy groups, resulting in a tetrafunctional branching point, as one can see in Fig. 1. For the reaction of anhydrides with epoxy groups, the presence of a small fraction of hydroxyl groups (e. g., secondary hydroxyl groups of oligomeric epoxies) is necessary.
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CH3 • HC-* СНг — 0 —C-<Q)—0- |
Table 1 Examples of Resin Components of Epoxies
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Table 2 Reaction Temperatures of Amine-Based Hardeners
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Figure 1 Cross-linking of epoxies by amines (simplified scheme). |
At elevated temperatures a hydroxyl group reacts with an anhydride and then the carboxylic group of the resulting half-ester reacts with an epoxy group to get an adduct, as one can see from Fig. 2. Epoxies may be polymerized through cationic polymerization, initiated by UV radiation (Fig. 3).
Acrylic resins used as adhesives are formed through radical or anionic polymerization [6]. Radical polymerization can be initiated by UV radiation as well as heat. The two reaction schemes are identical in principle (Fig. 4). Cyanoacrylates are of special interest for systems with very high reaction rates. Their reaction follows an anionic polymerization mechanism. Since the polarity of the cyanoacrylates is very high, water is able to act as an initiator (Fig. 5).
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