significant changes in its structure. For instance, while functionalizing PPA with an allyl acetate and tert-butyldimethylsilyl ether functional groups can lead to its rapid depolymerization in the presence of Pd(0) and F- respectively, a simple change in the nature of the endcaps will preserve the chain even in the presence of both corrosive agents. On a separate note, while PPA is insoluble in aqueous solvents and alcohols, it is highly soluble in organic solvents such as THF, DCM, and DMSO where it can be dissolved for days without triggering depolymerization. Applications Due to its unique stability, chemical properties, and outstanding tunability and reactivity, PPA has been employed in a variety of applications. Photoresist The high solubility and stability of PPA in organic solvents have allowed its investigation as a base material in first generation amplified photoresist for lithography in the early 80s by three scientists, Grant Willson, Jean Fréchet, and Hiroshi Ito who were working at IBM at the time. The story of how this successful achievement started and progressed can be found in the review paper written by Hiroshi Ito. Because PPA by itself does not undergo complete depolymerization upon its subjection to light, it is usually end-capped or used along photoacid generators (PAGs) for enhanced sensitivity. In this case, depolymerization is triggered upon irradiation either by end-cap removal and self-immolation or by the generated acid. Ober et al. stated that the use of PPA as photoresist under extreme ultraviolet (EUV) irradiation is yet to be successful due to the instability of PPA and the volatility of its monomers.30 However, they were able to report one of the first PPA derivatives without the use of PAGs with enhanced photoresist properties upon EUV exposure.19 Drug release Owing to its high reactivity and the ability to tune its endcap groups, PPA has been lately utilized in drug delivery applications. In one recent study, UV-sensitive PPA microcapsules containing different types of drugs were prepared. Once the capsules were subjected to a UV-light trigger, an unzipping reaction took place and the shell ruptured which led to the release of the core contain of these microcapsules. A unique advantage of these microcapsules is that they allow the immediate release of the drug upon exposure to the trigger rather than its continuous release over a period of time ranging from minutes to hours as other common microcapsules function. In an earlier publication, DiLauro et al.