Epichlorohydrin, cure systems

The development and optimisation is described of a new curing system to replace lead-based compounds used in epichlorohydrin elastomers currently used in automotive applications. The system is based on 2,4,6-trimercapto-1,3,5-triazine and dialkyldithiophosphate, which is shown to produce a scorch-safe curing system and which confers excellent physical and ageing properties on epichlorohydrin rubbers. Trials are conducted in formulations for multilayer fuel hoses. 9 refs. 

Hydantoin epoxy resins having glycidyl groups in the 1- and 3-positions and one or two alkyl groups in the 5-position were prepared by the Bucherer reaction, followed by treatment with epichlorohydrin. These resins were crosslinked with hexahydrophthalic anhydride to examine the effect of alkyl substituents on the glass transition temperatures of the cured systems. 

Uses Reactive epoxy diluent for solv.-free coating systems, laminating resins, fiber-reinforced composites, elec, applies. stabilizer for vi-nylidene chloride-vinyl chloride copolymers, chlorinated hydrocarbons chem. intermediate for pharmaceuticals curing system additive for bisphenol A-epichlorohydrin epoxies for food contact Regulatory FDA 21CFR 177.2280... 

Uses Modifier for elastomers, adhesives, fibers reactive diluent for epoxies reactive intermediate for coatings sizing/finishing agent for fiberglass silane intermediate in elec, coatings stabilizer of chlorinated compds., vinyl resins, rubber defoamer comonomer for polyepichlorohydrin rubber, unsat. polyester resins, and crosslinked PU elastomers curing system additive in bisphenol A-epichlorohydrin epoxies for food-contact articles... 

The cure of epoxidized novolaks, prepared via the reaction of Ph0H/CH2=0 copolymer with epichlorohydrin, in the presence of Nadic methyl anhydride, was studied by differential scanning colorimetry (DSC) [121]. The use of DSC to study other epoxy resin curing systems has been reported in the literature. 

Epoxy resin systems of the bisphenol A-epichlorohydrin t)rpe and epoxy novalac type generally lack flexibility. There are a number of proprietary flexible, low viscosity epoxy resins used to modify the above types to provide better impact resistance, elongation, or flexibility. These flexible epoxy resins are true epoxies and react completely with epoxy curing agents and becomes a permanent part of the cured system. However, they do not contribute towards lowering costs. 

A comparison of cure systems in epichlorohydrin-ethylene oxide copolymer (ECO) is shown in Table 13.12. ETU lead oxide cure system provides good technical properties, but is replaced because of health and environmental concerns. Vulcani-zates cured with non-lead cure systems generally have poorer properties after immersion in water. This can be overcome in the Zisnet cure system by the substitution of a synthetic hydrotalcite (Hysafe 310) for calcium oxide, with some sacrifice in compression set. The substitution of the hydrotalcite for lead oxide in the ETU cure system does not typically provide good water resistance... 

The A and B cure systems can be used in epichlorohydrin homopolymer (CO). The B and D cure systems can be used in unsaturated terpolymers (GECO). In addition, GECO can be cured with sulfur and peroxide cure systems. 

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. 

The lowest member of the series (n=o), the so-called Bisphenol-F resin, after glycylidation with epichlorohydrin, provided a low viscosity (4-6000 cP) liquid resin with slightly higher functionality and a more chemically resistant system after curing with... 

Cure conditions (temperature, time and catalyst S5retem) can be used to control particle development during cure if the resin/LR blend is miscible prior to cure. However, very few miscible systems have been developed. Figure 2 shows the fracture surface of a tough blend of vinyl ester with poly(epichlorohydrin) elastomer. This system is single phase before cure. Under the proper cure conditions a fine particulate phase develops as shown in Figure 3. 

---