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

Abstract

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).

Tuning Polymer Molecular Weight Distribution in Cationic RAFT Polymerization by Mixing Chain Transfer Agents†

“…[ 1‐4 ] However, efficient methods to precisely tune the polymer MWD in cationic polymerization haven't been well explored, which is essential for polymer properties such as mechanical properties, crystallization behavior, and viscoelasticity. [ 5‐7 ] In fact, it was until recent years some efficient strategies to tune polymer MWD have been developed such as metered additions of initiating species in controlled polymerization, [ 8‐9 ] blending polymers directly, [ 10‐12 ] or through combination with flow chemistry, [ 13‐18 ] tuning the components of the polymerization systems, [ 19‐26 ] and adjusting the external stimulus. [ 27‐34 ] In terms of cationic polymerization, Aoshima et al .…”

Quo Vadis Carbanionic Polymerization?

“…Recently, they reported a “locked-unlocked” mechanism in living anionic polymerization, where the anionic species can be quantitatively locked by end-capping with 1-(tri-isopropoxymethylsilylphenyl)-1-phenylethylene (DPE-Si­(O-iPr) 3 ) and subsequently unlocked by adding an alkali metal alkoxide (Figure ). The authors investigated the features of this mechanism by sequential feeding strategies, which revealed a new method for better controlling the composition, the molecular weight distributions, and the sequence of polymers. , …”

“…198 The authors investigated the features of this mechanism by sequential feeding strategies, which revealed a new method for better controlling the composition, the molecular weight distributions, and the sequence of polymers. 201,202 The controlled functionalization of polymers via living anionic polymerization, either at the chain-end or in-chain, has drawn great attention because it provides a route to various cross-linking reactions, branched architectures, and supramolecular noncovalent bonds, among others. 38 Toward this direction, many reports were documented by employing anionic polymerization and postpolymerization reactions for synthezing noncovalent bonded block polymers (hydrogen bonding, stereocomplexation, etc.).…”

On the Precise Determination of Molar Mass and Dispersity in Controlled Chain-Growth Polymerization: A Distribution Function-Based Strategy

“…Infinite possibilities of monomer combination in polymer molecules during polymerization endow polymers with less chain length uniformity presenting various molar mass distributions (MMD). Number- and mass-average molar masses and dispersity ( M n , M m , and Đ ) are the three key average properties of MMD, which critically associate with the mechanical properties of polymers and their processing behavior. − Controlled chain-growth polymerization is a powerful technique (e.g., controlled radical polymerization, controlled ring-opening metathesis polymerization) to produce well-defined polymers with predictable M n and low Đ (<1.5). − In recent years, precision design and regulation of MMD have gained much attention as an elegant way to alter the materials’ properties without changing chemical composition. − Naturally, precise information on the average properties of molar mass is essential in quantifying the level of control over polymerization or demonstrating the manipulation of the distribution.…”