text: 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. However, they were able to report one of the first PPA derivatives without the use of PAGs with enhanced photoresist properties upon EUV exposure.