Structural Manipulation of the Conjugated Phenyl Moiety in 3-Phenylbenzofulvene Monomers: Effects on Spontaneous Polymerization.

Spontaneous polymerization is an intriguing phenomenon in which pure monomers begin their polymerization without initiators or catalysts. Previously, 3-phenylbenzofulvene monomers were found to polymerize spontaneously after solvent removal. Here, eight new 3-substituted benzofulvene monomers 1a⁻h were synthesized in order to investigate the effects of differently substituted aromatic rings in position 3 of the benzofulvene scaffold on spontaneous polymerization. The newly synthesized monomers maintained the tendency toward spontaneous polymerization. However, monomer 1a, bearing an ortho-methoxy substituted phenyl, polymerized hardly, thus producing low polymerization yields, inhomogeneous structure, and low molecular weight of the obtained polymeric material. This result suggested the importance of the presence of hydrogen atoms in the 2'-position to achieve productive interactions among the monomers in the recognition step preluding the spontaneous polymerization and among the monomeric units in the polybenzofulvene backbones. Moreover, this study paves the way to modify the pendant rings in position 3 of the indene scaffold to synthesize new polybenzofulvene derivatives variously decorated.