Polycarbonates (Section 29.5C) are also formed by using a nucleophilic aromatic substitution route (Section 22.3B) involving aromatic difluoro monomers and carbonate ion. Propose a mechanism for this reaction.

Question: Describe the mechanism of polycarbonate formation via nucleophilic aromatic substitution. Answer: The mechanism of polycarbonate formation via nucleophilic aromatic substitution involves four steps: 1) nucleophilic attack of a carbonate ion on an electrophilic carbon in the aromatic ring, forming a sigma complex, 2) loss of a fluoride ion, restoring the aromatic ring's structure, 3) formation of a carbonate linkage (O-C-O) between two aromatic rings, and 4) polymerization with new difluoroaromatic monomers and carbonate ions, extending the polycarbonate chain. This mechanism leads to the formation of polycarbonates through nucleophilic attack, loss of fluoride ions, and polymerization.