Sacrificial Cyclic Poly(phthalaldehyde) Templates for Low-Temperature Vascularization of Polymer Matrices

Sacrificial polymers that depolymerize into small molecules upon exposure to an external stimulus facilitate the fabrication of synthetic structures with embedded vascular networks. Many sacrificial polymers such as poly(lactic acid) (PLA) and polycarbonates possess high thermal stability, leading to a time- and energy-intensive vascularization process. Furthermore, the use of these polymer templates is limited to high-temperature-resistant (>180 °C) matrices. Here, we demonstrate the rapid vascularization of a range of host matrices through the thermally triggered depolymerization of cyclic poly(phthalaldehyde) (cPPA) at temperatures near 100 °C. Complete mass loss of solvent-cast cPPA films is observed within 2 h at 100 °C in a thermogravimetric analyzer and after embedding in poly(dicyclopentadiene) matrices. The thermal processing of cPPA into sacrificial templates for inverse vascular architectures is hindered due to depolymerization at low temperatures. We successfully overcome these templating challenges by using solution spinning and 3D printing to fabricate fibers and printed templates, respectively. Microchannels are created inside low glass transition temperature (42 and 65 °C) epoxy-based matrices by depolymerizing the embedded fibers and printed templates within 1 h at 110 °C. This low-temperature cPPA evacuation protocol enables the vascularization of matrices that would not survive the harsh thermal cycle required for depolymerizing existing sacrificial polymers. Moreover, cPPA depolymerization affords a fivefold reduction in the thermal energy consumed during template removal compared to PLA.