Thermal conductivity of commodity polymers under high pressures

Heat flow in polymers under high-pressure conditions is essential for a range of applications, from aerospace and deep-sea engineering to common lubricants. However, the complex relationship between pressure, P, the thermal transport coefficient, κ, and polymer architecture poses substantial challenges to both experimental and theoretical investigations. In this work, we study the pressure-dependent thermal transport properties of a widely used commodity polymer-poly(methyl methacrylate)-using a combination of all-atom molecular dynamics simulations and semi-analytical approaches. We report both classical and quantum-corrected estimates of κ, both of which show an increase with increasing pressure P. The quantum-corrected approach, which is directly comparable to experiment, reveals that as the pressure increases from 1 atm to 10 GPa, κ rises by nearly a factor of four, from 0.21 to 0.80 W m-1 K-1. By comparison, experimental measurements report an increase from 0.20 to 0.55 W m-1 K-1 over the same pressure range. To better understand the mechanisms behind this increase, we disentangle the contributions from bonded and nonbonded monomer interactions. Our analysis shows that nonbonded energy-transfer rates increase by a factor of six over the pressure range, while bonded interactions show a more modest increase-about a factor of three. This observation further consolidates the fact that nonbonded interactions play the dominant role in dictating the microscopic heat flow in polymers. These individual energy-transfer rates are also incorporated into a simplified heat diffusion model to predict κ. The results obtained from different approaches show internal consistency and align reasonably with available experimental data. In addition, some data for polylactic acid are presented.