Low-Temperature Thermal Conductivity of Amorphous Polymers: Polystyrene and Polymethylmethacrylate

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Abstract
Measurements of the thermal conductivity between 4.5° and 1°K are reported for four commercial samples of polymethylmethacrylate and two commercial samples of polystyrene. It is shown that the thermal conductivity in this temperature range can be understood in terms of Klemens' theory of the thermal conductivity of amorphous substances in which the role of transverse vibrations is unimportant at low temperatures. Further, it is shown that the thermal conductivity of a partially oriented sample of polymethylmethacrylate is but slightly higher along the direction of stretch than for an unoriented sample; hence that vibrations along the polymer chains do not play a dominant role in the transport of heat at liquid‐helium temperatures. Indirect measurements of the specific heat of these substances have also been performed and yield C/T 3=735±50 erg/cm3‐(K°)4 for polystyrene and C/T 3=446±38 erg/cm3‐(K°)4 for polymethylmethacrylate.

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