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The stepwise addition polymerization reactions of bisazlactones [bis(2‐oxazolin‐5‐one)s] and a variety of 4,4′‐bisphenols have been studied for the purpose of making thermally reversible linear polymers. Thus polymerization occurs at or near room temperature, while depolymerization yielding the two monomer species occurs at elevated temperatures. The synthesis of oligomers in solution without the use of catalyst occurs for the reaction of bisazlactones with bisphenols containing an electron‐withdrawing moiety between the two phenol groups of the bisphenol. These oligomers regenerate the bisphenol and bisazlactone monomers upon heating to 165–200°C for several hours under dry box conditions. In many cases, these reactions follow the same patterns of reactivity observed in model studies. This chemistry may be useful for forming degradable or recyclable polymers, where shortchain prepolymers, or macromonomers, endcapped with azlactone and phenol moieties could be used to form high molecular weight polymers that are thermoreversible. Such a reaction system might also be used for preventing reactions of bisphenols and/or bisazlactones at low temperatures, with the desired reaction initiated by formation of the reactive species at elevated temperatures. Envisioned uses in this case might be thermally triggered crosslinking or polymerization reactions, or temperature controlled drug release. © 1993 John Wiley & Sons, Inc.

Research on the azlactone-phenol reaction has been extended to cross-linking chemistry. Poly-(2-vinyl 4,4-dimethyl-2-oxazolin-5-one) was used to synthesize three-dimensional networks using bisphenol cross-linkers. Among the bisphenols considered, only bisphenols containing electron-withdrawing groups at the site para to the phenol hydroxyls cross-link the polymer. The bisphenol 4,4'-(perfluorobutanediyl-1,4disulfonyl)diphenol was also found to facilitate the reverse reaction in high-boiling solvents, re-forming linear polymer and bisphenol at temperatures below the degradation temperature of the linear polymer. These networks undergo up to 20 or more cycles of cross-linking-de-cross-linking both inside and outside of the drybox.

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