Phenoxy Polymers
These materials are part of the technology of epoxy resins that are discussed in a separate section, further in this chapter. The polymers bridge a gap between thermosetting resins and thermoplastic polymers and are used in both forms commercially [116]. An idealized picture of phenoxy polymers can be shown as follows:
The polymer forms through caustic catalyzed condensations of diphenols with epichlorohydrin. Any diphenol or combination of diphenols can undergo this reaction. In commercial practice, however, mainly 4,4-isopropylidinediphenol, commonly called Bisphenol A, is used. Theoretically, the phenoxy resins should form in equimolar reactions of epichlorohydrin with the diphenol. There are, however, a number of side reactions that accompany the condensation. To get around them and to obtain high molecular weight polymers, the syntheses are carried out in two steps. In the first one, an excess of epichlorohydrin is used to form diepoxide:
In the second step, equimolar quantities of the diepoxide are reacted with the diphenol:
Both reactions are conducted in solution, where methyl ethyl ketone is the choice solvent. The commercial resins range in molecular weights from 15,000 to 200,000.
