We report measurements of the low-temperature thermal conductivity of diacetylene single crystals. Monomer samples show little anisotropy and display the temperature dependence of a crystalline dielectric. In polymerized samples, heat is conducted up to 60 times better parallel to the chains than perpendicular to them. Dislocations can account for this anisotropy at the lowest temperatures. Quasi one dimensionality of the polymer crystals induces anisotropy at higher temperatures and strongly suppresses anharmonic phonon interactions.

• Received 21 February 1986

DOI:https://doi.org/10.1103/PhysRevLett.57.869