Halogenated curing agents

Finally, apart from using halogenated epoxide resins or additives, it is also possible to use halogenated curing agents, examples being... 

The binder system of a plastic encapsulant consists of an epoxy resin, a hardener or curing agent, and an accelerating catalyst system. The conversion of epoxies from the Hquid (thermoplastic) state to tough, hard, thermoset soHds is accompHshed by the addition of chemically active compounds known as curing agents. Flame retardants (qv), usually in the form of halogens, are added to the epoxy resin backbone because epoxy resins are inherently flammable. 

The major brominated flame retardant used with epoxy resins is TBBA. This is a reactive halogenated intermediate incorporated during resin preparation. However, other bromine containing species plus phosphorus containing monomers or curing agents may be reacted with the main epoxy resin eomponents during polymerisation. The latter may be alkyl or aryl phosphates. The best appear to be phenyl phosphate derivatives. 

Flame Retardants. Flame retardance can be built into the epoxy resin by use of tetrabromobisphenol A or anhydride curing agents containing phosphorus or halogen. It can also be helped by nonreactive additives such as alumina trihydrate or organo-halogens + antimony oxide. 

These resins were designated as A, B, and C, and their halogen content and epoxy equivalent increased from A to C. In Figures 3.5 it can be seen that, for the same curing agent (BF3MEA), as the halogen content increased, the thermal stability decreased. This effect may be due to the presence of chlorinated structures, such as structure VI (Equation 3.31) ... 

Stannic chloride is also used widely as a catalyst in Eriedel-Crafts acylation, alkylation and cycHzation reactions, esterifications, halogenations, and curing and other polymerization reactions. Minor uses are as a stabilizer for colors in soap (19), as a mordant in the dyeing of silks, in the manufacture of blueprint and other sensitized paper, and as an antistatic agent for synthetic fibers (see Dyes, application and evaluation Antistatic agents). 

Properties Liq. m.w. 208.33 dec. 180 C Uses Crosslinking agent for elastomers, resins initiator for curing polyester resins finishing initiator for styrenics a synergist for some halogen-containing flame retardants polymer modifier... 

Phenolic resins are effective in conjunction with zinc oxide as cross-linking agents. Fast cures are possible with bromobutyl rubber without the need for adding halogen-containing compounds as in conventional butyl rubber. The products in this case have good dry heat resistance but inferior steam ageing resistance compared with the vulcanizates of unmodified butyl. 

Stearic acid and stearates may also be used as release agents, but NOT with a litharge cure system as scorching occurs and a short induction time during curing. Zinc stearates should be avoided in heat-resistant compounds as zinc chloride forms and lead to dehydro-halogenation of the polymer upon aging, or exposure to weather. 

Uses Processing aid for nat. and syn. rubber, e g., NR, SBR, and EPDM (except halogenated elastomers), esp. for extruded compds., but also for transfer and in], molding tiller dispersant cure activator flow aid, wetting agent, vise, reducer, vise, stabilizer in silica compds. food-contact rubber articles Regulatory FDA 21CFR 177.2600 and BGA approved Properties YIsh. pastilles sp.gr. 1.10 drop pt. 96 C 8.5% Zn Use Level 1-3 phr... 

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