Synthesis of Sequence-Controlled Homopolymer via Anionic Self-Alternating and Chemoselective Polymerization of 4-Vinyl-1,1-diphenylethylene Derivatives
Hamin Kim, Raita Goseki, Chihiro Homma, Takashi Ishizone
Abstract
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 (Ph 2 CHK) 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, M w / M n = 1.1–1.3). The 1 H and 13 C 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.