We quantify the thermal performance of these network polymers by TGA, DSC, CTE, and thermal conductivity. Similar to conventional polyimides, these polymers exhibit high thermal stability, with temperatures for 5 wt% degradation ranging from 368 °C to 385 °C (Figure , Table ), far above conventional solder reflow temperatures (265 °C). The CTE of the glassy polymers is 74-79 μm/m°C. Typical polyimide flexible electronic substrates such as Kapton HN® possesses a CTE of 20 μm/m°C at ambient conditions. CTE matching between substrate and mounted component is important to mitigate thermal stresses. It is important to note that all polymers exhibit an increase in CTE above their glass transition, including these systems (see SI). As crosslinked networks, thermosetting polymers can better maintain their shape under thermal cycling. Our PEIs also exhibit thermal conductivity ranging from 0.38 to 0.54 Wm -1 K -1 , which is higher than that of Kapton HN® (0.12 W m -1 K -1 ). Higher thermal conductivity is often desirable for heat dissipation. In fact, our neat photopolymers possess thermal conductivities similar to Kapton MT®, a commercial polyimide which contains additives specifically to improve its thermal conductivity (0.46 Wm -1 K -1 ). Together, these thermal properties compare well with commercial polyimides and even outperform in the case of thermal conductivity.