reported the ability to predesign and control the thickness of the microcapsule shells and length of the PPA used to form the shell, which have stimuli-responsive endcaps allowing head-to-tail fluoride-triggered depolymerization. Sensing through depolymerization PPA is known as a self-immolative material which depolymerizes through endcap cleavage in response to a specific stimulus. For this reason, several PPA polymers with different endcaps have been synthesized and used as self-immolative materials for sensing toxic and specific compounds. Acid-triggered depolymerization Due to the presence of two types of oxygen atoms in the PPA backbone, in addition to the fact that H+ tends to protonate oxygen atoms easily, depolymerization can occur through both endcap cleavage and protonation of oxygen atoms present in the backbone. For this reason, polymer chemists tend to use endcaps rich in oxygen atoms to accelerate depolymerization rate. For example, Moore and co-workers reported the use of a specific ion coactivation (SICA) effect that allowed the ion and acid coactivated-triggered depolymerization of a cyclic PPA microcapsules at the solid/liquid interface of the polymer and solution. Fluoride-triggered depolymerization Silyl groups can be deprotected with fluoride ions resulting in a strong Si-F bond that is hard and challenging to break. For this reason, different polymer chemists started to employ PPA in fluoride sensing by using t-butyldimethylsilyl (TBS) containing initiators and terminators. The fluoride sensing ability of PPA has been previously used in applications such as drug release, as previously reported by DiLauro et al. Another application studied by Phillips and co-workers includes the use of fluoride-triggered PPA depolymerization in changing the structure of plastics in a predetermined way. UV-light triggered depolymerization To demonstrate its capability in rapidly depolymerizing in presence of UV-light, DiLauro et al. synthesized a PPA polymer with two UV-sensitive endcaps, 2-nitro-4,5-dimethoxybenzyl alcohol and 1-[[(chlorocarbonyl)oxy]methyl]-4,5-dimethoxy-2 nitrobenzene, and were able to achieve complete depolymerization in a few minutes. In a practical application in organic electronics, cyclic PPA in the presence of 2-(4-methoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine (MBTT used as PAG) undergoes depolymerization upon exposure to UV-light, which in turn deactivates the transient electronics. Another similar application in transient electronics was reported where an organic light-emitting diode (OLED) was integrated on the PPA substrate and can cause depolymerization in the presence of a PAG. Pd(0)-triggered depolymerization Apart from its usage in sensing acids and fluoride anions, PPA has been used in sensing Pd(0) metal by employing allyl chloroformate as a terminating end cap. This has been reported