Curing of Glycidyl Ether Resins

Whilst the curing mechanisms may be quite complex and the cured resins too intractable for conventional analysis some indication of the mechanisms involved has been achieved using model systems. 

It has been shown in the course of this work that the reactivity of the epoxy ring is enhanced by the presence of the ether linkage separated from it by a methylene link. 

The epoxy ring may then be readily attacked not only by active hydrogen and available ions but even by tertiary amines. For example, with the latter it is believed that the reaction mechanism is as follows  

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

Since this reaction may occur at both ends of the molecule (in case of glycidyl ether resins) a cross-linked structure will be built up. 

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Curing of Glycidyl Ether Resins 751 26.3 CURING OF GLYCIDYL ETHER RESINS... 

Preparation of Resins from Bis-phenol A Curing of Glycidyl Ether Resins... 

In general, reactivity of amines toward aromatic glycidyl ethers follows their nucleophilicity aliphatic amines > cycloaliphatic amines > aromatic amines. Aliphatic amines cure aromatic glycidyl ether resins at room temperature (RT) without accelerators, whereas aromatic amines require elevated temperatures. 

The cycloahphatic products are generally Hquids of lower viscosity than the standard glycidyl ether resins. The peroxidized resins contain no chlorine and low ash content and their ring-contained oxirane group (cyclohexene oxide type) reacts more readily with acidic curing agents than the bisphenol A-derived epoxy resins. 

In adhesive formulations, aliphatic amines are most commonly used to cure the DGEBA type of epoxy resin. Aliphatic amines are not widely used with the non-glycidyl ether resins, since the amine-epoxy reaction is slow at low temperatures. The reaction usually requires heat and accelerators for an acceptable rate of cure. Aliphatic amines are primarily used with lower-viscosity DGEBA resins because of the difficulty in mixing such low-viscosity curing agents with the more viscous epoxy resins. 

The most widely used reactive diluents are based on derivatives of glycidyl ether. To be effective, the diluent should react with the curing agent at almost the same rate as the resin, contribute substantial viscosity reduction at low concentrations, and be nonreactive with the resin under normal storage conditions. 

Monofunctional aliphatic glycidyl ethers, eg, based on / -butanol or mixed Cg—alcohols, are used exclusively as reactive diluents to reduce viscosities of epoxy resin systems. Some loss of desirable cured properties results from the lowered functionality of the systems. 

Non-glycidyl ether epoxides Diluents, Rexibilisers tmd other Additives Structure and Properties of Cured Resins Applications... 

There are no reports of carcinogenic, mutagenic, teratogenic, or reproductive effects to humans ftom uncured resins, curing agents, or glycidyl ethers, but there are some positive... 

Cold curing unsaturated resin was obtained in the following way. A mixture of BPA, BPA monocyanate and BPA dicyanate was cyclotrimerized and reacted with BMI. The obtained prepolymer with phenolic hydroxyls (cf. Scheme 9) was then treated with epichlorohydrin and alkali. The phenolic hydroxyls were thus transformed into glycidyl ether groups. Then the addition of methacrylic acid to the epoxy groups was carried out. The obtained vinyl ester (epoxyacrylate) type resin was dissolved in styrene and cured with the usual benzoyl peroxide/dimethylaniline system [131],... 

Glycidyl Ethers of Aliphatic Polyols. Glycidyl ether epoxy resins based on polyols provide greater flexibility and lower softening temperatures for the final cured epoxy system. The polyol is reacted with epichlorohydrin to produce these resins. These resins are generally not used alone because of water sensitivity and overall lack of toughness. However, they serve as modifiers for DGEBA-based epoxy resins. An idealized structure for a flexible resin based on this chemistry is shown in Fig. 2.9. 

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