The thermal behaviour of a series of side-chain liquid crystalline poly(methacrylates) has been investigated by thermogravimetry, differential scanning calorimetry, polarizing optical microscopy, and dilatometry. The DSC study has shown that long times are required to reach equilibrium even at temperatures above the glass transition. The thermotropic polymorphism has been determined as a function of the length of the flexible spacer. Glass transitions in the mesomorphic state have been discussed. Dilatometry has shown that, for the « glassy » mesomorphic phases, the partial specific volume of the flexible spacer is close to that corresponding to the crystalline state ; that, for the normal liquid crystalline phases, it is intermediate between those corresponding to the crystal and the isotropic liquid ; and that, for the isotropic polymer, it is close to that of a liquid.