requires highly sensitive reaction conditions and is more time demanding, this type of polymer has many advantages over its cyclic counterpart. For instance, a control over the polymer’s molar mass can easily be achieved by controlling the monomer and alcohol initiator ratios. Furthermore, it has been proven to be more thermally stable than its cyclic counterpart due to the presence of functionalized endcaps that stabilizes the polymer chain from depolymerization. For these reasons, it has been studied to a far greater extent than cyclic PPA. Various linear PPA with distinct end groups have been reported (Figure 4) and studied for a variety of applications including sensing, drug delivery, and lithography. For instance, once these end groups are cleaved as a response to the exposure of PPA to a specific stimulus, the polymer will sequentially disassemble from head to tail through an unzipping reaction to form the monomer in short times that can be as low as a few minutes. Cyclic PPA Cyclic PPA is obtained through a cationic polymerization of o-phthalaldehyde using a Lewis acid, typically Boron trifluoride etherate, as an initiator. When Aso and Tagami first reported the successful synthesis of PPA using this technique in 1967, they were unaware of the fact that the polymer they prepared was cyclic and instead reported the structure as linear in their research paper. It was not until 2013 that polymer chemists proved that the structure is cyclic using a combination of characterization techniques including Nuclear Magnetic Resonance (NMR), Fourier Transform Infrared Spectroscopy (FT-IR), Gel Permeation Chromatography (GPC), and Mass Spectrometry (MS). Cyclic PPA is easy to synthesize; it is reported by Prof. Jeffrey Moore that the cationic polymerization of o-phthalaldehyde is very fast, yielding cyclic PPA within few minutes. Furthermore, the polymer can be isolated without the addition of pyridine nor methanol nor a strong base terminator, which in general makes this polymerization technique easy, fast, and cheap. Nevertheless, a known issue of this technique is the fact that the molecular weight cannot be controlled based on the initial concentration of the monomer used, which has led typically to cyclic PPA with a wide variety of molecular weights ranging between 3 kDa to 100 kDa using the same starting conditions. Furthermore, because of its cyclic structure, no end caps are used or needed. The absence of functionalized end caps in the structure has limited the usage of cyclic PPA especially in