Designing Thermally Conductive Two-Dimensional Polymer Films

Kiana Treaster¹, Rupam Roy¹, Yuxing Liang², Shravan Godse², Ayan Majumdar³, Jonathan Malen², Pramod Sangi Reddy³, and Austin M. Evans¹

1 University of Florida, 2 Carnegie Mellon University, 3 University of Michigan

The poor thermal conductivity (0.1-0.3 W m^-1 K^-1) observed in polymers is typically rationalized by the limited thermal transport in amorphous materials held together by weak intermolecular interactions. Recent reports have shown that highly thermally conducting polymers (> 1 W m^-1 K^‑1) can be achieved by enhancing polymer crystallinity, increasing macromolecular chain alignment, and reinforcing inter-chain non-covalent interactions. However, these findings have not yet driven comprehensive synthetic efforts to expose how different macromolecular features impact thermal conductivity. Here, we synthesize four distinct imine-linked two-dimensional polymer (2DPs) thin films with varying combinations of nodes (tetraphenylamino-pyrene and -perylene) and linkers (terephthaldehyde and biphenyldicarboxyaldehyde) to probe structure-property relationships. This subset of systems allows us to perform pairwise comparisons with the aim of uncovering structure-property design rules for high thermal conductivity polymers. The 2DPs are then post-synthetically modified to transform the imine-linked frameworks to an amide and amine-linked framework to further investigate how different covalent linkages impact anisotropic thermal conductivity. The 2DPs were characterized using infrared spectroscopy, X-ray diffraction, porosimetry, and atomic force microscopy. The cross-plane thermal conductivity (k_⟂)  was determined using frequency domain thermoreflectance and the in-plane thermal conductivity (k_∥) was determined using a suspended platform device. 2DP films were successfully synthesized and shown to have a maximum k_⟂= 0.20 W m^-1 K^-1 and k_∥=1.10 W m^-1 K^-1. After transforming the imine-linked framework to an amide-linked framework, the k_⟂increased to 0.29 W m^-1 K^-1. These results showcase how structure features reliably impact thermal conductivity in soft matter systems.