Thermal expansion and compressibility in the chain direction of a polydiacetylene single crystal

An x‐ray back‐reflection rotating camera has been used to measure the lattice constant, thermal expansion, and compressibility in the polymer chain direction of a polydiacetylene, poly[bis( p ‐toluene sulfonate) of 2,4‐hexadiyne 1,6‐diol]. The thermal expansion coefficient of the polymer chain is small and positive (0.9 ± 0.2 × 10 −6 °K − ) at 300°K, but negative below about 70°K. Application of 3.43 kbar hydrostatic pressure at 299°K changed the unit cell dimension in the polymer chain direction by less than 10 ppm.