Stimuli-responsive polymers capable of autonomous self-destruction upon receiving a triggering cue have been of recent research interest for polymer recycling and transient electronics. Cyclic poly(phthalaldehyde) (cPPA) is a thermodynamically metastable polymer that undergoes rapid solid state depolymerization when triggered and has been used as an encapsulating and packaging material in the fabrication of physically transient systems. Herein, the metastability of cPPA is discussed and control over the depolymerization trigger is shown. Both photo and thermal triggering events are demonstrated to produce rapid depolymerization events that transform a stiff bulk polymer film into a crystalline powder when photo-depolymerized or sublimated vapor when thermally-depolymerized. In both cases, the depolymerization of cPPA leads to the recovery of the monomeric product <i>ortho</i>-pthalaldehyde, which can be repolymerized to recover cPPA. Due to the intrinsically metastable design of the cPPA, processing methods were largely limited to solvent-casting efforts that limited exposure to high temperatures. The solvent-cast films were stiff with elastic moduli between 2.5 and 3 GPa and thermodynamic properties which were heavily dependent on the boiling point of the solvent used for casting. Since thermal instability and the practical limitations of solvent-casting precluded many applications, efforts were made to stabilize cPPA for thermal processing. It was found that careful and thorough removal of the latent Lewis acid catalyst boron trifluoride diethyl etherate and the addition of a radical inhibitor or Lewis base greatly delayed the onset of thermal depolymerization. The added stabilization allowed for thermoforming of cPPA for the first time, vastly expanding on its utility as a bulk transient material building block future applications. <br/>

Triggerable, solid-state depolymerization of bulk thermoformable cyclic poly(phthalaldehyde)

2019 Fall National Meeting

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