The kinetics of the polycondensation of 3,5-bis(trimethylsiloxy)benzoyl chloride (BTMSBC1) was investigated. 1D and 2D NMR techniques were applied to achieve a complete signal assignment of the structural units of the resulting polymer (poly(3,5-dihydroxybenzoic acid), PDHBA), which was obtained after hydrolysis of the trimethylsiloxy and the acid chloride groups. Furthermore, the diads could be identified. After quantification of the signals by C-13 NMR spectroscopy, a data set of ratios of structural units as a function of the conversion had been studied with respect of the kinetics of the system and their resulting structural composition. Since the data do not follow the ideal conversion dependence, the relative rate constants of the 12 different basic reaction steps were determined by simulation, which fit the obtained data best. A study of the sensitivity of the reaction curves to changes in the individual rate constants showed large differences and helped to distinguish the importance of the different basic reactions to the overall reaction. One kinetic situation was identified as dominant. The deviations (from the ideal conversion dependence) were explained by different electronic effects on the reaction sites caused by the successive substitution of siloxy and benzoyl chloride groups by ester groups on the aromatic ring. Analysis of the data for the diads indicated no further kinetic effect.