In this study, a quantitative structure–property relationship (QSPR) study is carried out to estimate the physical properties of substituted polypyrrole (PPy) and polyparaphenylene (PPP). The effects of the substituted side-chains composed of ε-caprolactone, ethylene and styrene oligomers on the glass transition temperature, cohesive energy and dielectric constant of PPy and PPP are studied and the results are analyzed in terms of backbone structure, the type and the length of the side-chains. It is shown that the Tg of the polymers can be lowered upon substitution of flexible side-chains. The cohesive energy is higly dependent on the the strength of the non-bonded interactions and it is increased by incorporation of flexible side-chains. The dielectric constant of the polymers is found to be increased depending on the polarizability and the dipole moment density of the side-chains.