Acid-catalyzed cross-linking reactions at benzylic sites in fluorene monomers, polymers, and lignin

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