Aqueous RAFT Polymerization of Acrylonitrile

Chemoselective, Postpolymerization Modification of Bioactive, Degradable Polymers

Degradable polymers promote sustainability, mitigate environmental impact, and facilitate biological applications. Tailoring degradable polymers is challenging because installing functional group-rich side chains is difficult when the backbone itself is susceptible to degradation. A convenient means of side chain installation is through postpolymerization modification (PPM). In functionalizing polyoxazinones, a class of degradable polymers generated by the ring-opening metathesis polymerization (ROMP), we predictably found PPM challenging. Even the versatile azide-alkyne cycloaddition click reaction was ineffective. To solve this problem, we screened PPM reactions whose efficiencies could be assessed using photochemistry (excimer formation). The mildest, pH-neutral process was functionalization of a ketone-containing polymer to yield either oxime (acid labile)- or alkyoxylamine (stable)-substituted polymers. Using this approach, we equipped polymers with fluorophores, reporter groups, and bioactive epitopes. These modifications imbued the polymers with distinctive spectral properties and biological activities. Thus, polyoxazinones are now tunable through a modular method to diversify these macromolecules' function.

Polyamidoxime chain length drives emergent metal-binding phenomena

Emergence is complex behavior arising from the interactions of many simple constituents that do not display such behavior independently. Polyamidoxime (PAO) uranium adsorbents show such phenomena, as recent works articulate that the polymer binds uranium differently than the monomeric constituents. In order to investigate the origins of this emergent uranium-binding behavior, we synthesized a series of amidoxime polymers with low polydispersity and small molecules with lengths ranging from 1 to 125 repeat units. Following immersion in a uranyl-containing solution, the local, intermediate, and macroscopic structures were investigated by X-ray absorption fine structure (XAFS) spectroscopy, small angle neutron scattering (SANS), and dynamic light scattering (DLS). Fits of the extended XAFS (EXAFS) region revealed a progressive change in uranium coordination environment as a function of polymer molecular weight, identifying chain length as a driving force in emergent metal binding and resolving the controversy over how amidoxime adsorbents bind uranium.

Redox-Initiated Reversible Addition–Fragmentation Chain Transfer (RAFT) Polymerization

Reversible addition–fragmentation chain transfer (RAFT) polymerization initiated by a radical-forming redox reaction between a reducing and an oxidizing agent (i.e. ‘redox RAFT’) represents a simple, versatile, and highly useful platform for controlled polymer synthesis. Herein, the potency of a wide range of redox initiation systems including enzyme-mediated redox reactions, the Fenton reaction, peroxide-based reactions, and metal-catalyzed redox reactions, and their application in initiating RAFT polymerization, are reviewed. These redox-RAFT polymerization methods have been widely studied for synthesizing a broad range of homo- and co-polymers with tailored molecular weights, compositions, and (macro)molecular structures. It has been demonstrated that redox-RAFT polymerization holds particular promise due to its excellent performance under mild conditions, typically operating at room temperature. Redox-RAFT polymerization is therefore an important and core part of the RAFT methodology handbook and may be of particular importance going forward for the fabrication of polymeric biomaterials under biologically relevant conditions or in biological systems, in which naturally occurring redox reactions are prevalent.

Reversible Addition-Fragmentation Chain Transfer Polymerization of Acrylonitrile under Irradiation of Blue LED Light

Compared to unhealthy UV or γ-ray and high-energy-consumption thermal external stimuli, the promising light emitting diode (LED) external stimulus has some outstanding technological merits such as narrow wavelength distribution, low heat generation and energy consumption, and safety for human beings. In this work, a novel reversible addition-fragmentation transfer (RAFT) polymerization system for acrylonitrile (AN) was developed under the irradiation of blue LED light at room temperature, using 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) as a novel radical initiator and 2-cyanoprop-2-yl-1-dithionaphthalate (CPDN) as the typical chain transfer agent. Well-defined polyacrylonitrile (PAN) with a controlled molecular weight and narrow molecular weight distribution was successfully synthesized. This strategy may provide another effective method for scientific researchers or the industrial community to synthesize a PAN-based precursor of carbon fibers.