Search

An innovative process to multifunctional vitrimer nanocomposites with a percolative MXene minor phase is reported, marking a significant advancement in creating stimuli-repairable, reinforced, sustainable, and conductive nanocomposites at diminished loadings. This achievement arises from a Voronoi-inspired biphasic morphological design via a straight-forward three-step process involving ambient-condition precipitation polymerization of micron-sized prepolymer powders, aqueous powder-coating with 2D MXene (Ti 3 C 2 T z ), and melt-pressing of MXene-coated powders into crosslinked films. Due to the formation of MXene-rich boundaries between thiourethane vitrimer domains in a pervasive low-volume fraction conductive network, a low percolation threshold (≈0.19 vol.%) and conductive polymeric nanocomposites (≈350 S m -1 ) are achieved. The embedded MXene skeleton mechanically bolsters the vitrimer at intermediate loadings, enhancing the modulus and toughness by 300% and 50%, respectively, without mechanical detriment compared to the neat vitrimer. The vitrimer's dynamic-covalent bonds and MXene's photo-thermal conversion properties enable repair in minutes through short-term thermal treatments for full macroscopic mechanical restoration or in seconds under 785 nm light for rapid localized surface repair. This versatile fabrication method to nanocoated pre-vitrimer powders and morphologically complex nanocomposites is compatible with classic composite manufacturing, and when coupled with the material's exceptional properties, holds immense potential for revolutionizing advanced composites and inspiring next-generation smart materials., (© 2024 Wiley‐VCH GmbH.)

Adhesives are ubiquitous in manufacturing spanning nearly all sectors from healthcare and photovoltaics to aerospace and electronics. Yet many commercial polymers remain challenging to adhere, necessitating either pretreatment, mechanical fastening, or adhesive processes that involve specialized equipment, high temperature/vacuum, and long cure times. Thus, rapid-cure adhesives for polymers that can set under ambient conditions using simple procedures are desirous because they offer cost savings, faster production, and greater design freedom to producers. Herein, we report a powerful adhesive platform that bonds a wide scope of commodity polymers via (hydrogen) atom transfer and free-radical (graft) polymerization initiated with a trialkylborane-ligand complex and isocyanate decomplexing agent. The developed adhesive formulation is air-stable, bulk, and operates in air at room temperature using a high-glass-transition temperature polyacrylate, i.e., poly(isobornyl acrylate). The alkylborane-initiated bonding process is rapid (∼30 min), requires minimal surface preparation (cleaning and mild roughening), and successfully bonds seven diverse substrates including polytetrafluoroethylene, polyethylene, polypropylene, polycarbonate, nylon, polymethylmethacrylate, and polyvinylchloride. This contribution uniquely investigates the process-property relationships for the adhesive formulation, lap-shear performance, mechanism of failure, and a reactive additive for enhancing the adhesive's glass-transition temperature to ∼120 °C (polyhedral oligomeric silsesquioxane or POSS) to widen its operation temperature. We envision that the reported alkylborane-initiated adhesion platform could hold promise in the automotive, aerospace, and marine sectors as means for rapid manufacturing and structural adhesion., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

Thiol-ene nanocomposites were synthesized for the first time using an alkylborane-ligand initiator complex under bulk and ambient conditions without external light or thermal stimuli. Initiation was triggered by the in situ decomplexation of an air-stable trialkylborane-amine complex to liberate trialkylborane, which rapidly autoxidizes with atmospheric oxygen and generates free radicals to drive thiol-ene polymerization. This chemically activated mode of initiation uniquely affords thiol-ene nanocomposites with an unrivaled carbon nanotube (CNT) loading of 1.3 wt % and thicknesses of ∼6.7 mm by circumventing restrictions imposed by long pathlengths and light-impeding fillers during photoinitiation. Alkylborane initiation also exhibited advantageous polymerization rates, equivalent to photoinitiation, resulting in network formation and gelation within minutes. Systematic studies were conducted to evaluate comparable alkylborane- and photo-initiated nanocomposites under progressively higher loadings and larger specimen thicknesses, revealing an enhancement or better retainment of mechanical performance in alkylborane-initiated nanocomposites.

Nanoparticle synthesis was demonstrated via functionalization-induced self-assembly (FISA) of block copolymers using Suzuki-Miyaura cross-coupling. In situ self-assembly was triggered in organic media by the progressive installation of solvophobic pendant groups onto an initially soluble diblock copolymer, rendering the reactive block insoluble and causing the formation of spherical polymeric micelles. Self-assembly was found to depend on the percent functionalization ( f % ), where after a critical threshold micelles were accessible that increased in size with increasing f % values. We found the chemical nature of the installed functional group to be crucial for conducting FISA and for controlling the solution morphology, with relatively solvophilic adducts remaining as unimers and increasingly solvophobic adducts trending toward larger micelles, from ca. 40 to 100 nm in diameter. The core and corona of the anticipated micellar structure were visualized using fluorine mapping through electron energy loss spectroscopy, in conjunction with FISA achieved through pendent trifluorophenyl functionality. This work establishes FISA as a new, versatile synthetic strategy to create nanoparticles having tunable morphologies with potential application as molecular payload delivery vehicles.

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.

The synthesis and application of a very active catalyst for copper-catalyzed atom transfer radical polymerizations (ATRP) with tris([(4-methoxy-2,5-dimethyl)-2-pyridyl] methyl)amine (TPMA*) ligand is reported. Catalysts with TPMA* ligands are approximately 3 orders of magnitude more active than those with tris(2-pyridylmethyl)amine (TPMA). Catalyst activity was evaluated by cyclic voltammetry, stopped-flow, and ATRP kinetics. Catalysts with TPMA* ligands perform better than those with TPMA ligands, especially at low catalyst concentrations.

A series of 2,2'-bipyridines with 4,4'-substituents (R-bpy) were investigated for atom transfer radical polymerization (ATRP) of methyl acrylate (MA) and methyl methacrylate (MMA). Ligand substituents with a large range of Hammett parameters (R = Cl, H, Me, dinonyl (dN), MeO, and (Me) 2 N) were studied with cyclic voltammetry (CV), revealing that increasing the strength of electron donating groups (EDGs) resulted in more stable Cu II complexes and larger ATRP equilibrium constants. Normal ATRP experiments confirmed the obtained CV data by showing the fastest rates of polymerization with R-bpy ligands containing EDGs ((Me) 2 N and MeO) and the slowest with electron withdrawing Cl. A 400-fold increase in the polymerization rate was observed with bpy ligands containing p -(Me) 2 N compared to H substituents. Linear increases in molecular weight with monomer conversion, and narrow molecular weight distributions were obtained with (Me) 2 N-bpy and MeO-bpy ligands. Low catalyst concentrations of 50 to 100 parts-per-million (ppm) were successfully employed with highly active R-bpy ligands (R = MeO and (Me) 2 N) and found to be effective in polymerizing MA and MMA, respectively, with narrow molecular weight distributions <1.3.

Atom transfer radical polymerization (ATRP) methods were developed in water-based media, to grow polymers from proteins under biologically relevant conditions. These conditions gave good control over the resulting polymers, while still preserving the protein's native structure. Several reaction parameters, such as ligand structure, halide species, and initiation mode were optimized in water and PBS buffer to yield well-defined polymers grown from bovine serum albumin (BSA), functionalized with cleavable ATRP initiators (I). The CuCl complex with ligand 2,2'-bipyridyne (bpy) provides the best conditions for the polymerization of oligo(ethylene oxide) methacrylate (OEOMA) in water at 30 °C under normal ATRP conditions (I/CuCl/CuCl 2 /bpy = 1/1/9/22), while the CuBr/bpy complex gave better performance in PBS. Activators generated by electron transfer (AGET) ATRP gave well-controlled polymerization of OEOMA at 30 °C with the ligand tris(2-pyridylmethyl)amine (TPMA), (I/CuBr 2 /TPMA = 1/10/11). The AGET ATRP reactions required slow feeding of a very small amount of ascorbic acid into the aqueous reaction medium or buffer. The reaction conditions developed were used to create a smart, thermoresponsive, protein-polymer hybrid.