Tacticity-dependent cross-plane thermal conductivity in molecularly engineered amorphous polymers
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 been widely found to enhance heat transfer in both a single polymer chain and bulk polymers. Here, we show that the tacticity of polymers (i.e. poly(acrylic acid) (PAA), poly(methacrylic acid) (PMAA)) significantly affect thermal conductivity in ionized polymers, in which extended chain conformation is induced by electrostatic repulsion. Depending on their tacticity, polymers with the similar degree of ionization were observed to have significantly different thermal conductivities, as high as 1.14 W/m∙K in ionized atactic PAA and 0.69 W/m∙K in ionized syndiotactic PMAA but merely 0.55 W/m∙K in ionized isotactic PAA and 0.48 W/m∙K 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 impacts on the conformation of the polymer chain, affect the thermal conductivity in polymers.