Thermal Conductivity of Pentiptycene-Based Poly(o-hydroxyimide) Copolymers: A Study via Integrated Experiments and Simulations

Polymers play important roles in thermal transport applications, and conjugated polymers have been identified as promising candidates to achieve high thermal conductivity. In this paper, pentiptycene-based poly(o-hydroxyimide) (PPHI)-conjugated copolymers, made of a bulky pentiptycene segment and a −CF3 substituent segment, with different segment ratios are studied. Both experimental and molecular dynamics (MD) simulation results show that polymer thermal conductivity increases as the ratio of the bulky segment increases. The experimental in-plane thermal conductivity is significantly higher than the out-of-plane value (up to 6.38 times), which is due to the chain alignment effect in the in-plane direction. The highest measured in-plane thermal conductivity reaches 0.982 W/m·K, which is among the highest in polymer thermal conductivity. Experimental results show that the volumetric heat capacity increases with the bulky segment ratio which should have a positive impact on the thermal conductivity. MD results further show that the bulky segment helps increase the spatial extension of polymer chains and the amount of strong interatomic forces related to the aromatic carbon atoms, both leading to increasing thermal conductivity. In addition, we also find that the fractional free volume in the PPHI copolymers decreases as the bulky segment ratio increases, which should also have contributed to the increase in thermal conductivity.