Achieving molecular weight distribution shape control and broad dispersities using RAFT polymerizations

Abstract

Reversible addition-fragmentation chain-transfer (RAFT) polymerizations are one of the most versatile and powerful polymerization techniques for the synthesis of complex macromolecular architectures. While RAFT polymerizations often give polymers with narrow...

Controlling the shape of the molecular weight distribution for tailored tensile and rheological properties in thermoplastics and thermoplastic elastomers

“…21,23,24,36,39,40,43,44 In 2016, with inspiration from the early works of Meira and Aoshima, our group developed a modular strategy for precisely controlling MWD breadth and shape via temporal initiation, in which discrete chain-initiating species are added over time to a one-pot reaction for deterministic control over polymer chain length. We have utilized this general strategy in various controlled radical polymerizations, 47,48 ionic polymerizations, [49][50][51][52][53][54][55] and coordination-insertion polymerizations. 56 Due to the living characteristics of these F I G U R E 1 Tensile and rheological characterization reveal the effects of MWD shape on material properties F I G U R E 2 Illustration for the calculation of asymmetry factor (A s ), which is equal to the length of A divided by the length of B at 10% peak height polymerization techniques, our strategy has enabled the synthesis of well-defined homopolymers as well as block copolymers-wherein the first block has a skewed MWD (Figure 3).…”

Tuning Ligand Concentration in Cu(0)-RDRP: A Simple Approach to Control Polymer Dispersity

“…One of the elegant approaches for tuning dispersity is the temporal regulation of initiation method developed by Fors and co-workers, where the initiator is fed in throughout a polymerization, so polymer chains start growing at different times. ,,− In addition, the groups of Boyer, Junkers, Frey, Leibfarth, Guironnet, and others have independently introduced a range of flow approaches, where dispersity can be carefully controlled by adjusting reaction parameters. − These methods are often associated with excellent mathematical modeling and the ability to be automated, allowing desired molecular weight distributions to be obtained. ,− ,, Furthermore, several batch methods have been recently developed to tune polymer dispersity. − These include reducing the catalyst concentration in atom transfer radical concentration (ATRP), ,,− mixing high and low activity chain transfer agents in reversible addition–fragmentation chain transfer (RAFT) polymerization, , adjusting the solvent polarity and concentration of azide in reversible complexation-mediated polymerization, and using photochromic initiators to control dispersity in cationic polymerization . Other reported methods involve the modification of CRPs by either addition of a comonomer or a termination agent ,, or blending prepurified polymers of either different molecular weight or dispersity. , Despite these excellent recent breakthroughs, there are only limited techniques that can give access to well-defined polymers with controlled dispersity, hindering the widespread use of these materials.…”

Tailoring polymer dispersity by mixing ATRP initiators

“…For example, Fors and co-workers pioneered the field by introducing a clever feeding method to tune the shape and the breadth of molecular weight distributions. In particular, the initiating species were accurately fed in nitroxidemediated, 12 anionic, 13 coordination 14 and RAFT 15 polymerizations at predetermined rates resulting in a continued initiation process and full control over the MWDs. The same group subsequently studied the effect of skewness and shape of MWDs in mechanical properties and bulk self-assembly.…”