Unlocking features of locked-unlocked anionic polymerization†
Due to unique characteristics of 1-(tri-isopropoxymethylsilylphenyl)-1phenylethylene (DPE-Si(OiPr)3), quantitative locked (the living species became dormant for endcapping with DPE-Si(OiPr)3) and unlocked (the dormant species regained the activity after adding the alkali metal alkoxides) anionic polymerization has been realized. In this work, the features of locked-unlocked anionic polymerization were carefully investigated with sequential feeding strategies. By combining the results from SEC, 1H-NMR, MALDI-TOF-MS and DFT calculations, the main features of this mechanism were revealed as follows: (1) it is a kinetically controlled process (kDS and kSS) due to the inherent features of different living species. Comparable initiation and propagation rates are required to ensure the simultaneous chain growth from unlocked living species; (2) the transformation between locked and unlocked species depends on the alkalinity of the alkali metal alkoxides; the higher the alkalinity, the higher the unlocking efficiency. And promisingly, these findings may contribute to the modulation of molecular weight distribution and facilitate the preparation of position-defined functionalized polymers in the future.