Polymer molecular weight, or chain length distributions, are a core characteristic of a polymer system, with the distribution being intimately tied to the properties and performance of the polymer material. A model is developed for the ideal distribution of polymers made using reversible activation/deactivation of chain ends, with monomer added to the active form of the chain end. The ideal distribution focuses on living chains, with the system having minimal impact from irreversible termination or transfer. This model was applied to ATRP, RAFT, and cationic polymerizations, and was also used to describe complex systems such as blended polymers and block copolymers. The model can easily and accurately be fitted to molecular weight distributions, giving information on the ratio of propagation to deactivation, as well as the mean number of times a chain is activated/deactivated under the polymerization conditions. The mean number of activation cycles per chain is otherwise difficult to assess from conversion data or molecular weight distributions. Since this model can be applied to wide range of polymerizations, giving useful information on the underlying polymerization process, it can be used to give fundamental insights into macromolecular synthesis and reaction outcomes.
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Achieving molecular weight distribution shape control and broad dispersities using RAFT polymerizations
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 molecular weight distributions (MWDs), commodity plastics often have broad MWDs to give targeted properties and processability. Thus, new methods to precisely control both MWD breadth and shape are essential for fine-tuning polymer properties for next generation materials. Herein, we report a simple method for controlling polymer MWD features in thermally activated radical RAFT and redox activated cationic RAFT polymerizations by means of metered additions of chain transfer agents.
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- Award ID(s):
- 1901635
- NSF-PAR ID:
- 10249099
- Date Published:
- Journal Name:
- Polymer Chemistry
- ISSN:
- 1759-9954
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Oxygen tolerant polymerizations including Photoinduced Electron/Energy Transfer-Reversible Addition–Fragmentation Chain-Transfer (PET-RAFT) polymerization allow for high-throughput synthesis of diverse polymer architectures on the benchtop in parallel. Recent developments have further increased throughput using liquid handling robotics to automate reagent handling and dispensing into well plates thus enabling the combinatorial synthesis of large polymer libraries. Although liquid handling robotics can enable automated polymer reagent dispensing in well plates, photoinitiation and reaction monitoring require automation to provide a platform that enables the reliable and robust synthesis of various polymer compositions in high-throughput where polymers with desired molecular weights and low dispersity are obtained. Here, we describe the development of a robotic platform to fully automate PET-RAFT polymerizations and provide individual control of reactions performed in well plates. On our platform, reagents are automatically dispensed in well plates, photoinitiated in individual wells with a custom-designed lightbox until the polymerizations are complete, and monitored online in real-time by tracking fluorescence intensities on a fluorescence plate reader, with well plate transfers between instruments occurring via a robotic arm. We found that this platform enabled robust parallel polymer synthesis of both acrylate and acrylamide homopolymers and copolymers, with high monomer conversions and low dispersity. The successful polymerizations obtained on this platform make it an efficient tool for combinatorial polymer chemistry. In addition, with the inclusion of machine learning protocols to help navigate the polymer space towards specific properties of interest, this robotic platform can ultimately become a self-driving lab that can dispense, synthesize, and monitor large polymer libraries.more » « less
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ABSTRACT Electrochemically mediated atom transfer radical polymerizations (ATRPs) provide well‐defined polymers with designed dispersity as well as under external temporal and spatial control. In this study, 1‐cyano‐1‐methylethyl diethyldithiocarbamate, typically used as chain‐transfer agent (CTA) in reversible addition–fragmentation chain transfer (RAFT) polymerization, was electrochemically activated by the ATRP catalyst CuI/2,2′‐bipyridine (bpy) to control the polymerization of methyl methacrylate. Mechanistic study showed that this polymerization was mainly controlled by the ATRP equilibrium. The effect of applied potential, catalyst counterion, catalyst concentration, and targeted degree of polymerization were investigated. The chain‐end functionality was preserved as demonstrated by chain extension of poly(methyl methacrylate) with
n ‐butyl methacrylate and styrene. This electrochemical ATRP procedure confirms that RAFT CTAs can be activated by an electrochemical stimulus. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem.2019 ,57 , 376–381 -
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Abstract Reversible addition‐fragmentation chain transfer (RAFT) polymerization has proven itself as a powerful polymerization technique affording facile control of molecular weight, molecular weight distribution, architecture, and chain end groups ‐ while maintaining a high level of tolerance for solvent and monomer functional groups. RAFT is highly suited to water as a polymerization solvent, with aqueous RAFT now utilized for applications such as controlled synthesis of ultra‐high molecular weight polymers, polymerization induced self‐assembly, and biocompatible polymerizations, among others. Water as a solvent represents a non‐toxic, cheap, and environmentally friendly alternative to organic solvents traditionally utilized for polymerizations. This, coupled with the benefits of RAFT polymerization, makes for a powerful combination in polymer science. This perspective provides a historical account of the initial developments of aqueous RAFT polymerization at the University of Southern Mississippi from the McCormick Research Group, details practical considerations for conducting aqueous RAFT polymerizations, and highlights some of the recent advances aqueous RAFT polymerization can provide. Finally, some of the future opportunities that this versatile polymerization technique in an aqueous environment can offer are discussed, and it is anticipated that the aqueous RAFT polymerization field will continue to realize these, and other exciting opportunities into the future.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D1PY00399B
