Polymer composed of macromolecules containing exclusively alternating phenylene or substituted phenylene and ethynediyl (formerly ethynylene) constitutional repeating units 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, alkyl, aryl, halogen, trialkylsilyl etc. (structure-based polymer class name).