Polyacetals and polyketals

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. 

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Polyacetals and polyketals are polyethers that form (1) through condensations of glycols with carbonyl compounds, (2) by exchange reactions of acetals or ketals, and (3) by additions of diols to dialkenes ... 

The reaction of polyvinyl alcohol to give polyacetals or polyketals has been already described in Vol. II of this series. In addition the conversion of polyhydrazides to polyoxadiazoles, and polymeric acids to polyimides is also described in Vol. I of this series [14] and in Section 5 of this chapter. 

Polyacetals or polyketals can be made by most of the methods shown in Schemes 1 and 2 starting with diols, polyols, or polythiols in place of the alcohols [1]. The use of poly(vinyl alcohol) gives either poly(vinyl acetals) or poly(vinyl ketals) and is described in Section 7 in this chapter. 

Additionally, acid-degradable protein delivery vehicles have been synthesized via ADMET polymerization [126]. In this work, ADMET was used to form polyketals and polyacetals, which possessed the physical properties necessary for microparticle formulation. Using a double emulsion procedure, the enzyme, which catalyzes the decomposition of hydrogen peroxide to water and oxygen, was encapsulated into these microparticles. Cell studies demonstrated that these microparticles dramatically improved the ability of the catalase to scavenge hydrogen peroxide produced by macrophages. 

Polyvinyl alcohol related polymers provide solubilization of a pesticide bound as a side chain. Polyacetals, polyketals, and poly-q-esters... 

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