P-PHENYLENETETRAMETHYLENE DIRADICAL AND ZWITTERION INTERMEDIATES IN THE SPONTANEOUS COPOLYMERIZATIONS OF ELECTROPHILIC P-QUINODIMETHANES WITH ELECTRON-RICH OLEFINS

Electrophilic p-quinodimethanes react spontaneously with electron-rich olefins to form either homopolymers of electron-rich olefins or alternating copolymers. In analogy with the bond-forming initiation theory proposed for the spontaneous reactions observed between electrophilic olefins and electron-rich olefins, a similar mechanism is proposed for the electrophilic p-quinodimethane/electron-rich olefin reactions. A bond is formed between the electrophilic p-quinodimethane and the electron-rich olefin. The resulting p-phenylenetetramethylene intermediate may possess either predominantly zwitterionic or diradical nature, depending on the substituents. Zwitterionic intermediates initiate cationic homopolymerization of the electron-rich olefin, while diradical ones initiate free-radical alternating copolymerization between the two participants. A “periodic table” is constructed to give a rational structure-reactivity correlation. To delineate more clearly the line between diradical and zwitterion mechanisms, additional experimental data are provided using p-methoxystyrene and phenyl vinyl ether as the electron-rich olefins. © 1990, American Chemical Society. All rights reserved.