Tacticity-dependent cross-plane thermal conductivity in molecularly engineered amorphous polymers

Abstract

The low thermal conductivity of polymers impedes heat dissipation in plastic products and often limits their functionality and reliability. Extended polymer chain conformation (i.e., planar zigzag) has widely been found to enhance heat transfer in both a single polymer chain and bulk polymers. Here, we show that the tacticity of polymers (poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA)) significantly affects the thermal conductivity of ionized polymers, in which the extended chain conformation is induced by electrostatic repulsion. Depending on their tacticity, polymers with similar degrees of ionization were observed to have significantly different thermal conductivities, as high as 1.14 W m⁻¹·K⁻¹ in ionized atactic PAA and 0.69 W m⁻¹·K⁻¹ in ionized syndiotactic PMAA, but only 0.55 W m⁻¹·K⁻¹ in ionized isotactic PAA and 0.48 W m⁻¹·K⁻¹ in ionized isotactic PMAA. The elastic modulus, degree of ionized carboxyl groups, and viscosity data suggest that the size and spatial arrangement of side groups, which influence the conformation of the polymer chain, affect the thermal conductivity of polymers.