A soluble rigid-rod macromonomer is provided which has the following formula: ##STR1## wherein each G.sub.1, G.sub.2, G.sub.3, and G.sub.4, on each monomer unit, independently, is H or a solubilizing side group, provided that at least one monomer unit has at least one solubilizing side group. The solubilizing side groups provide the macromonomers with a solubility of at least 0.5% by weight in the solvent system from which they are formed. E is a reactive end group, and the macromonomer has an average degree of polymerization, DP.sub.n, greater than 6. Such macromonomers are chemically incorporated into polymer systems to provide stronger stiffened polymers.