In the following thesis the thermotropic phase transition behaviour and structure-property-relations of semiflexible polyesters were investigated. These materials can be used in fibre optical blood-pressure sensors as resonator materials in a Fabry-Perot-Interferometer. PVT-measurements were carried out to determine the thermodynamic parameters alphaV(T) and kappa(P), and the validity of the Ehrenfest equations at glass transition temperatures was verified. These latter investigations showed no thermodynamic second order transition. By using alphaV(T) and kappa(P) for the calculation of the resonator-length-difference, the temperature- and pressure behaviour of the investigated polyesters was simulated. This simulation showed that small variations in the resonator length from increasing pressure agrees with the empirically determined values. An increasing number of methylene groups in the sidechain of the spacer molecule resulted in decreased melting- and glass transition temperature, which revealed the possibility to prepare thin polymer-films with 5-10 micrometer in diameter at low temperatures.