Polyphthalaldehyde: Synthesis, Derivatives, and Applications

o-Phthalaldehyde is, to this day, the only aromatic aldehyde that can be homopolymerized through chain-growth polymerization. The product, polyphthalaldehyde (PPA), is a brittle white solid, and, having a polyacetal main chain, presents the ability to depolymerize quite rapidly in the presence of an acid. This review highlights the unique polymerization chemistry of o-phthalaldehyde since its discovery over half a century ago, describing the different methods for the preparation of PPA and its derivatives, how the polymerization chemistry affects the structure and thermomechanical properties of the obtained PPA, and summarizes recent developments in PPA chemistry as a responsive material. Modern material applications such as the use of PPA as photoresists or in thermal-scanning probe lithography, as well as exploration of judiciously end-capped PPA for its use as self-immolative materials are summarized. In addition, the use of PPA blocks in copolymers is described, leading to the development of films with well-defined nanochannels or nanopores that can serve as a template for the preparation of the microorganization of nanomaterials.