A reversible addition−fragmentation chain transfer (RAFT) process was developed capable of being performed at room temperature and in the presence of oxygen by initiating polymerization through an alkylborane−amine complex. This air-stable alkylborane−amine complex was chemically deblocked with carboxylic acid or isocyanate functionalities to liberate a reactive trialkylborane that consumes oxygen and generates radicals to mediate RAFT. Alkylborane-initiated RAFT (AI-RAFT) was demonstrated to allow the synthesis of a wide range of polymer molecular weights with narrow distributions. Rapid polymerization was also possible within minutes under an ambient environment without any prior deoxygenation. Optimal conditions were investigated revealing that carboxylic acids are required in larger excess to alkylborane versus isocyanates and that deblocker functionality can have an impact on polymerization kinetics, achievable molecular weight, and dispersity. Living chain-ends were confirmed by synthesizing block copolymers using AI-RAFT-derived macro-chain transfer agents. In this preliminary study, a chemically induced RAFT process is introduced without requirement of any thermal, photochemical, electrical, or mechanical stimulus capable of polymerizing acrylamide, acrylate, and methacrylate monomers in limited amounts of oxygen at room temperature.

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The first MXene discovered, Ti3C2T z , was synthesized by etching aluminum, Al, from the nanolaminated MAX phase, Ti3AlC2, using hydrofluoric acid, HF. To delaminate the resulting MXene multilayers, MLs, it was necessary to increase the interlayer spacing, by first treating them with relatively large organic cations such as tetrabutylammonium hydroxide, TBAOH, dimethyl sulfoxide, DMSO, etc. When etched with a combination of LiF and HCl on the other hand, the Li cations spontaneously intercalated and no extra delamination step was needed. Herein, we attempt to understand why some molecules intercalate into the HF-etched MXene, while others do not. We find that treating HF-etched Ti3C2T z MLs with a base, like NaOH, renders them ion exchangeable. This base treatment was found to reduce the −F terminations on the MXene surfaces, which most likely weakens the interlayer hydrogen bonding and therefore allows for ion exchange and concomitant hydration. We exploit this nucleophilic dehalogenation to functionalize the Ti3C2T z surfaces using several different nucleophiles like sodium stearate, lithium ethoxide, and diisopropyl xanthogen polysulfide. We also demonstrate the effect of interlayer ions and other functional terminations on the electrochemical performance of Ti3C2T z in sodium ion and lithium sulfur batteries. Finally, we find that the interlayer spacing between MXene sheets derived using LiF + HCl increases dramatically when exposed to low-concentration salt solutions; this was attributed to osmotic swelling. This phenomenon was earlier observed in clays but is shown for the first time in the case of MXenes.

Despite the excellent mechanical and electrical performance of MXene−polymer nanocomposites, methods for producing these materials on a larger scale are limited by low-yielding, delaminated, MXene suspensions that are typically employed for their synthesis. Moreover, the hydrophilicity of MXenes restricts the production of well-dispersed nanocomposites with many polymer matrices. In this contribution, we address such limitations and report, for the first time, a simple method to covalently modify multilayered Ti 3 C 2 T z MXenes with isocyanates, which enables their successful dispersion within a hydrophobic thiourethane matrix. The efficacy of our covalent modification was determined to yield high levels of surface grafts and suggests quantitative conversion of the oxygen-containing terminations. In situ-polymerized thiourethane "click" matrices were used to demonstrate the utility of this modification for accessing well-dispersed nanocomposites under ambient conditions. The ease of producing modified, multilayered, MXenes at scale and the availability of a wide variety of isocyanates render this method scalable and highly modular. Furthermore, the reported isocyanate treatment was found to be a valuable tool for easily quantifying the concentration of reactive (oxygen-containing) terminations on MXene surfaces.

An alkylborane initiated reversible addition-fragmentation chain transfer (AI-RAFT) process was developed for the synthesis of star-polymers using a onepot approach at room-temperature in the presence of oxygen. Linear poly(tertbutyl acrylate) arms were first polymerized using a latent trialkylborane-amine initiator, which generated trialkylborane, in situ, and subsequently radicals after reaction with oxygen. Polymerizations were optimized to maximize monomer conversion (~70-80%) and minimize arm-dispersity (~1.10) through the oxygen concentration, initiator concentration, and polymerization time.The oxygen concentration was a critical AI-RAFT parameter, providing maximum conversion at a~0.5:1 molar ratio of oxygen-to-initiator. After arm-polymerization, multifunctional acrylates were injected into the reactor to commence crosslinking without intermediate purification. The impact of the crosslinking time and the crosslinker's functionality, concentration, and injection time were investigated to enhance arm incorporation and diminish starpolymer dispersity, quantified by deconvolution of size-exclusion chromatography data. Crosslinker concentration had the largest influence on arm conversion with optimal concentrations at a 20-25-fold excess to chain transfer agent.Under optimal conditions, arm conversions were maximized to~75-85% and star-dispersity minimized to~1.35-1.50. Herein an initial effort is made toward the synthesis of star-polymers with well-defined structures and high-arm conversions, while also striving for oxygen tolerance, minimal purification, lowtemperatures, and metal-free conditions. K E Y W O R D S star polymers, reversible addition fragmentation chain transfer, alkylborane initiation, oxygen tolerant, room temperature, controlled radical polymerization