Polymers composed of macromolecules containing exclusively $\mathrm{\sigma }$-bonded benzene or substituted benzene rings in the backbone: where $\mathrm{R}{\phantom{A}}^1$, $\mathrm{R}{\phantom{A}}^2$, $\mathrm{R}{\phantom{A}}^3$ and $\mathrm{R}{\phantom{A}}^4$ are each hydrogen or an univalent group (structure-based polymer class name).