Controlling Polymer Molecular Weight Distribution through a Latent Mediator Strategy with Temporal Programming

Abstract

Polymer molecular weight distribution (MWD) is a key parameter of polymers. Here we present a robust method for controlling polymer MWD in controlled cationic polymerizations. A latent mediator strategy was designed and combined with temporal programming to regenerate mediators at different times during polymerization. Both the breadths and shapes of MWD curves were tuned easily by adjusting an external light source. Bimodal, trimodal, and tetramodal distributions were obtained, and the breadths could be varied from 1.06 to 2.09. Polymers with different MWDs prepared by this method had good chain end fidelity, which was demonstrated with successful chain-extension experiments. In addition, the introduction of temporal programming with a computer-controlled single chip for the light source opened an avenue for the use of artificial intelligence in polymer synthesis.

Catalyst-Free, Visible-Light-Induced Step-Growth Polymerization by a Photo-RAFT Single-Unit Monomer Insertion Reaction

“…35 Our previous work reported a photo-RAFT SUMI reaction between a radical-type RAFT agent and a vinyl ether monomer to generate a cationic RAFT agent under UV or visible light (Scheme 1A). 36,37 We speculate that the combination of vinyl ether and radical-type RAFT agents will provide an AB-type monomer for step-growth polymerization (Scheme 1B). Similarly, a bifunctional vinyl ether and a RAFT agent can be used as the A 2 + B 2 -type monomers (Scheme 1C) for the step-growth polymerization.…”

Living Covalent-Anionic-Radical Polymerization via a Barbier Strategy

“…Even though different mechanisms, species, or strategies are involved in the development of these living polymerization methods, they fundamentally derive from organic synthetic methods. For example, the living anionic polymerization was based on an electron transfer reaction and developed in 1956; − the living group transfer polymerization was based on silyl ketene acetal being involved in a Michael reaction and developed in 1983; , the living cationic polymerization was based on olefin protonation and developed in 1984; , the living ring-opening metathesis polymerization was based on an olefin metathesis reaction and developed in 1986; , the reversible-deactivation radical polymerization (RDRP) methods, including but not limited to stable-radical-mediated polymerization, atom transfer radical polymerization, reversible addition–fragmentation chain transfer polymerization, and so on, were developed mainly in the 1990s based on the corresponding reversible-deactivation radical reactions. − In these living polymerization methods, different strategies are carried out to keep living chain propagation by minimizing undesired chain termination. Generally, living anionic polymerization is realized through a charge repulsion strategy, with anionic species exhibiting no chain termination, even at a monomer conversion reaching >99%.…”

Turbo-Grignard Reagent Mediated Polymerization of Styrene under Mild Conditions Capable of Low Đ and Reactive Hydrogen Compatibility

“…To achieve polymers with low Đ , living polymerization methods of alkene monomers have been developed, which have inspired comprehensive applications of polymer materials in the fields of drug delivery, self-assembly, sensors, and so on. − Generally, these living polymerizations can be achieved through anionic, cationic, or radical species. − In the past decades, living polymerization has gained considerable progress, and different living polymerization methods have been developed. − For example, Szwarc developed living anionic polymerization of styrene (St) by using sodium naphthalenide as initiator to precisely control macromolecular architectures, molecular weight, and Đ in 1956 . Inspired by Szwarc’s landmark work in living anionic polymerization, many remarkable living polymerization methodologies have been developed. − In 1983, Webster and co-workers reported group transfer polymerization of α,β-unsaturated carbonyl compounds by using silyl ketene acetals as initiators. , Subsequently, Higashimura and co-workers discovered living cationic polymerization of isobutyl vinyl ether with HI/I 2 as initiating systems in 1984. , Grubbs and co-workers achieved living ring-opening metathesis polymerization of norbornene using metallacyclobutanes as catalysts in 1986. , Reversible deactivation radical polymerizations (RDRP) have gained great progress since the 1990s, including atom transfer radical polymerization by using specific alkyl halides as initiators with the presence of transition-metal complexes, nitroxide-mediated radical polymerization using nitroxides as stable free radicals, reversible addition–fragmentation chain transfer polymerization using thiocarbonyl chain transfer agents, and so on. − Throughout these landmark works on living polymerization, minimizing chain termination is the key point to keep living chain propagation, which is realized by introducing different strategies.…”