Synthesis of Sequence-Controlled Homopolymer via Anionic Self-Alternating and Chemoselective Polymerization of 4-Vinyl-1,1-diphenylethylene Derivatives

Anionic polymerization of AB-type difunctional monomers derived from 4-vinyl-1,1-diphenylethylene (VD) bearing styrene and 1,1-diphenylethylene (DPE) frameworks was examined using diphenylmethylpotassium (Ph2CHK) in THF at −78 to 0 °C. A series of substituents including chloro (ClVD), methyl (MeVD), methoxy (MeOVD), and dimethylamino (Me2NVD) groups were introduced at the 4′-position of the VD framework to vary the polymerizability of VD. In each case, the resulting polymer was soluble and possessed the predicted molecular weight and a narrow molecular weight distribution (Đ, Mw/Mn = 1.1–1.3). The 1H and 13C NMR measurements and MALDI-TOF-MS analysis revealed that a "self-alternating polymerization" of ClVD, MeVD, and MeOVD yielded a linear homopolymer with an (AB)n-type alternating sequence through the intermolecular cross-propagation chain-growth mechanism. In particular, the resulting poly(ClVD) exhibited only an odd-numbered degree of polymerization, indicating a mechanism of exclusive initiation and subsequent self-alternating polymerization of the VD derivative. In contrast, Me2NVD underwent the usual chemoselective polymerization in the styrene framework to yield an (A)n-type sequence because the electrophilicity of the DPE unit of Me2NVD was highly reduced. Thus, the electronic effect of the substituents determines the polymerization behavior of the VD derivatives.