Free-Radical Polymerization of Dibenzofulvene Leading to a π-Stacked Polymer:  Structure and Properties of the Polymer and Proposed Reaction Mechanism

Free-radical polymerization of dibenzofulvene (DBF) was carried out under various conditions. The radical polymerization proceeded exclusively in vinyl fashion without isomerization of the growing radical or aromatic substitution by the initiator fragment. The polymerization was highly conformation-specific (stereospecific), giving a polymer with a π-stacked conformation in which the main-chain C−C bonds are nearly all trans and the side-chain fluorene moieties are stacked on top of each other. The conformation specificity (stereospecificity) of the DBF radical polymerization was almost similar to that in the anionic polymerization although the radical polymerization products appeared to have a small amount of irregular, defective conformation incorporated into the mostly π-stacked chain. The conformation specificity was affected by the initial monomer concentration and reaction temperature. This observation was explained by a proposed mechanism where two types of the growing radicals having different conformations mediate the polymerization. The poly(DBF) obtained by the radical polymerization showed lower fluorescent intensity and higher solubility possibly due to a small amount of conformational defects.