The acid-catalyzed polymerization of benzylic alcohol and fluoride functionality in monomeric and polymeric fluorenes was investigated in both organic and aqueous reaction media. Polymeric products are consistent with the generation of benzylic cations that participate in electrophilic aromatic substitution reactions. Similar reactions occurred in a water-insoluble Kraft pine lignin, by treatment with aqueous acid. The acid treatment produced 1-2 cross-links/100 carbons in the biopolymer and markedly decreased its solubility in organic solvents. The nature of the reactions which produced the insoluble biopolymer are inferred from solid-state (CP/MAS) C-13 NMR spectra.