Manipulating Molecular Weight Distributions via “Locked–Unlocked” Anionic Polymerization

A significant example for modulating molecular weight distributions (MWDs) in living anionic polymerization (LAP) based on the “locked–unlocked” feature is reported. The locked–unlocked feature means that the anionic species can be temporarily “locked” while chains propagating by capping with 1-(4-triisopropoxysilylphenyl)-1-phenylethylene (DPE-Si(OiPr)3) and can be “unlocked” by adding alkali metal alkoxide. The capping reaction rate plays an important role in controlling MWDs, which reasonably relies on the relative concentration between DPE-Si(OiPr)3 and the carbanion. Thus, two strategies (i.e., intermittent and continuous) were proposed in this work to regulate MWDs. By an intermittent strategy, the MWD was flexibly adjusted from mono to multimodal, and by a continuous strategy, the symmetry of the monomodal curves (Đ = 1.07–1.39, As = 0.65–1.55) was controlled. Moreover, by taking advantage of the “unlocked” feature of the living end, a series of Si–H functionalized block copolymers (PS-b-P(St-alt-DPE-SiH)n, i.e., PS-b-PSD) derived from MWD-controlled polystyrenes were successfully synthesized, and then grafted copolymers (PS-b-PSD-g-(PIp)n) with varied MWDs were prepared using hydrosilylation. Additionally, the relationships between MWDs and the thermodynamic behaviors were determined by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC).