A new quantitative model is proposed to correlate glass transition temperatures with bond radii-based structural parameters for poly(p-alkyl styrenes), polyolefins, poly(alkyl methacrylates), and poly(alkyl acrylates). The model provides a consistent prediction of the glass transition temperatures for both the linear and highly branched polymers up to the entanglement offset points for long side groups. Polymers with highly branched side chains, such as t-butyl and t-pentyl groups that contain quaternary C groups, are predicted to have much higher glass transition temperatures, followed by the methylated, the unsubstituted, and the linearly alkylated polymers. The predictions are confirmed by the experimental results from the authors’ research and literature. The current model also allows the extraction of the contribution of hydrogen bonding to glass transition temperatures in polymethacrylates and polyacrylates by comparing differences between the modeled hydrogen-bonding free values with the experimental data.