Toward Controlled Gilch Synthesis of Poly(p-phenylenevinylenes): Synthesis and Thermally Induced Polymerization of α-Bromo-p-quinodimethanes

It is general consensus that in Gilch polymerizations the 1,4-bis(halomethylene)benzene starting material first changes into an α-halo-p-quinodimethane intermediate which then acts as the real active monomer in the subsequent chain growth process. Recently, we could verify the formation of α-chloro-p-quinodimethane directly via in-situ NMR spectroscopy at low temperatures. However, quantitative formation of this p-quinodimethane was not possible there. Now, we show that even such quantitative conversion into the active monomer is possible if bromomethylene-functionalized starting materials are used instead of their chloromethylene counterparts. Moreover, it is even possible to induce chain growth leading to PPV in a very controlled way by carefully warming the obtained solution of p-quinodimethane. In this manner, the temperature can be determined where chain growth startsand hence thermal energy is sufficient for the initiating process. Finally, we could reconfirm that the chain growth is a radical polym...