Polymer composed of macromolecules containing exclusively alternating phenylene or substituted phenylene and methylene or substituted methylene constitutional units in the backbone: where \(\ce{R^1}\), \(\ce{R^2}\), \(\ce{R^3}\), \(\ce{R^4}\), \(\ce{R^5}\), and \(\ce{R^6}\) are each hydrogen, alkyl, aryl, halogen, trialkylsilyl, etc.