The influence of the molecular parameters of side-on fixed liquid crystal polymers (LCP), namely the spacer length, the aliphatic tail length and the proportion of mesogenic groups ('dilution' effect), on the mesomorphic, thermodynamic and structural properties of the nematic and smectic C phases has been studied. This shows in particular the stabilization of the SmC phase on increasing the terminal chain lengths. Moreover, this paper provides evidence for an original behaviour in the SmC organization of side-on LCP with a nonstructural monotonous evolution of the thermodynamic and properties with the 'dilution'. Finally, a comparison with side-end LCP can be established : the question of the participation of the polymer backbone in the smectic organization in side-on LCP is raised.