Unlocking features of locked-unlocked anionic polymerization

Abstract

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 (k_DS and k_SS) 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.