Carbon of course can only share four pairs of electrons at once, so one pair has to go if it wants to take the oxygen's pair. So it lets go of the electrons it has been sharing with chlorine, and sends the chlorine atom on its way, expelling it from the molecule. Click here to see a movie of this step of the reaction. We end up with a molecule similar to bisphenol A, only with an epoxy group on it. And we also get NaCl.
Different things can happen.
Remember on the epoxy page we talked about how these prepolymers come in different molecular weights. Sometimes the degree of polymerization is as high as 25. A salt groups left to react. A salt groups can react with epichlorohydrin. Click here to see a movie of this step of the reaction.