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Where does the chlorine go? Does it evaporate as a by-product or does it remain in the epoxy? I'm using a two-part resin and hardener and curing them at room temp. The resin is bisphenol-A-epichlorohydrin, and I believe the final cured epoxy does not have chlorine as a part of its main structure. I need to know the whereabouts of Cl because I'm trying to study neutron interaction with materials in my detector, and I suspect there's some chlorine in there but not sure entirely.

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There is little if any chlorine in a epichlorohydrin / bis phenol A expoxy resin, it is normally lost during production as sodium chloride into the aqueous phase while the resin forms an organic phase.

The normal way to make the resin is to react bisphenol A with sodium hydroxide and the epichlorohydrin. What happens is that a mixture of the three reagents and water is heated up together. The phenol groups on the bisphenol A are deprotonated and then they attack the epichlorohydrin to then form 2,2'-(((propane-2,2-diylbis(4,1-phenylene))bis(oxy))bis(methylene))bis(oxirane). The epoxide (oxirane) groups in this then react with phenolate anions from new bisphenol A molecules to form 4,4'-((((((propane-2,2-diylbis(4,1-phenylene))bis(oxy))bis(2-hydroxypropane-3,1-diyl))bis(oxy))bis(4,1-phenylene))bis(propane-2,2-diyl))diphenol. The unreacted phenol groups on this then are reacted with more epichlorohydrin to form new reactive groups.

This reaction continues on and on to form a polymer, it is normal to use a small excess of epichlorohydrin to give a epoxy terminiated polymer (resin). This is then reacted with a cross linking agent such as an amine to form the final epoxy. As a result the chlorine content of the epoxy should be very very low.

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    $\begingroup$ So to answer the OP's question, the chlorine goes into aq phase as NaCl. $\endgroup$ – Waylander Jun 20 '18 at 9:45
  • $\begingroup$ I thought that if you read the answer it is clear where the chlorine goes to, but I have made it even more obvious. $\endgroup$ – Nuclear Chemist Jun 20 '18 at 10:48
  • $\begingroup$ @Waylander Thanks! So the aq. NaCl remains in the cured final epoxy volume right? And this amount should NOT be too low, am I correct? $\endgroup$ – Betsy Jun 20 '18 at 16:11

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