Open-Air Chemical Recycling: Fully Oxygen-Tolerant ATRP Depolymerization.

While oxygen-tolerant strategies have been overwhelmingly developed for controlled radical polymerizations, the low radical concentrations typically required for high monomer recovery render oxygen-tolerant solution depolymerizations particularly challenging. Here, an open-air atom transfer radical polymerization (ATRP) depolymerization is presented, whereby a small amount of a volatile cosolvent is introduced as a means to thoroughly remove oxygen. Ultrafast depolymerization (i.e., 2 min) could efficiently proceed in an open vessel, allowing a very high monomer retrieval to be achieved (i.e., ∼91% depolymerization efficiency), on par with that of the fully deoxygenated analogue. Oxygen probe studies combined with detailed depolymerization kinetics revealed the importance of the low-boiling point cosolvent in removing oxygen prior to the reaction, thus facilitating effective open-air depolymerization. The versatility of the methodology was demonstrated by performing reactions with a range of different ligands and at high polymer loadings (1 M monomer repeat unit concentration) without significantly compromising the yield. This approach provides a fully oxygen-tolerant, facile, and efficient route to chemically recycle ATRP-synthesized polymers, enabling exciting new applications.

Reversible Transformations of Polymer Topologies through Visible Light and Darkness.

A fundamentally important characteristic of a macromolecule is its shape. Herein, visible light and darkness are used as the only stimuli to reversibly alter the topology of well-defined polymers in a one-pot procedure. For this, linear naphthalene-containing polyacrylates are used as scaffolds for the visible light-induced cycloaddition with various substituted triazolinediones (i.e., butyl, stearyl, perfluoro, and polymeric), resulting in differently shaped graft polymers, including brushes and combs. The thus-formed cycloadduct linkages dissociate in the dark, resulting in the regeneration of the parent linear polymer at ambient temperature, establishing a dual-topology transformation by only switching green light on and off. By applying different temperatures during the cycloreversion process, the dissociation rate of the cycloadducts can be tuned in a facile manner, thus allowing for time control over the regeneration of the parent polymer. By engineering a polymer that consists of differently substituted naphthalenes at the chain ends and on the side chains, the inherently different cycloreversion rates of the formed cycloadducts are leveraged to achieve in situ multi-topology transformations without external stimuli. The shape transformations have been repeated up to 4 times sequentially in one pot without the need of any purification. The topological alterations are microscopically depicted through reversible self-assembly, with the polymers adopting different morphologies upon visible light or darkness. The versatile yet practical nature of this polymer "reshaping" strategy provides facile access to multifaceted polymer systems and, consequently, to a plethora of potential applications thereof.

Automatic peak assignment and visualisation of copolymer mass spectrometry data using the 'genetic algorithm'.

Copolymer analysis is vitally important as the materials have a wide variety of applications due to their tunable properties. Processing mass spectrometry data for copolymer samples can be very complex due to the increase in the number of species when the polymer chains are formed by two or more monomeric units. In this paper, we describe the use of the genetic algorithm for automated peak assignment of copolymers synthesised by a variety of polymerisation methods. We find that in using this method we are able to easily assign copolymer spectra in a few minutes and visualise them into heat maps. These heat maps allow us to look qualitatively at the distribution of the chains, by showing how they alter with different polymerisation techniques, and by changing the initial copolymer composition. This methodology is simple to use and requires little user input, which makes it well suited for use by less expert users. The data outputted by the automatic assignment may also allow for more complex data processing in the future.

Copper-Mediated Reversible Deactivation Radical Polymerization in Aqueous Media.

Key advances within the past 10 years have transformed copper-mediated radical polymerization from a technique which was not very tolerant of protic media into a range of closely related processes capable of controlling the polymerization of a wide range of monomers in pure water at ppm catalyst loadings. This approach has afforded water-soluble macromolecules of desired molecular weight, architecture, and chemical functionality, with applications ranging from drug delivery to oil processing. In this Review we highlight and critically evaluate the synthetic methods that have been developed to control radical polymerization in water by using copper complexes as well as identify future areas of interest and challenges still to be overcome.

Copper-Mediated Polymerization without External Deoxygenation or Oxygen Scavengers.

As a method for overcoming the challenge of rigorous deoxygenation in copper-mediated controlled radical polymerization processes [e.g., atom-transfer radical polymerization (ATRP)], reported here is a simple Cu0 -RDRP (RDRP=reversible deactivation radical polymerization) system in the absence of external additives (e.g., reducing agents, enzymes etc.). By simply adjusting the headspace of the reaction vessel, a wide range of monomers, namely acrylates, methacrylates, acrylamides, and styrene, can be polymerized in a controlled manner to yield polymers with low dispersities, near-quantitative conversions, and high end-group fidelity. Significantly, this approach is scalable (ca. 125 g), tolerant to elevated temperatures, compatible with both organic and aqueous media, and does not rely on external stimuli which may limit the monomer pool. The robustness and versatility of this methodology is further demonstrated by the applicability to other copper-mediated techniques, including conventional ATRP and light-mediated approaches.

Localised polymerisation of acrylamide using single-barrel scanning electrochemical cell microscopy.

Single-barrel scanning electrochemical cell microscopy has been adapted for polymerisation of acrylamide in droplet cells formed at gold electrode surfaces. Localised electrochemical atom transfer radical polymerisation enables controlled synthesis and deposition of polyacrylamide or synthesis of polyacrylamide brushes from initiator-functionalised electrode surfaces.

Synthesis and [2+2]-photodimerisation of monothiomaleimide functionalised linear and brush-like polymers.

[2+2]-Photodimerisation of monothiomaleimides has been demonstrated on functionalised linear and brush-like polymers. In water/acetonitrile (95 : 5) mixtures the rate of reaction is accelerated significantly by irradiation of the thiomaleimide end group (λmax = 350 nm) with UV light, reaching full conversion within 10 minutes.

Rapidly self-deoxygenating controlled radical polymerization in water via in situ disproportionation of Cu(i).

Rapidly self-deoxygenating Cu-RDRP in aqueous media is investigated. The disproportionation of Cu(i)/Me6Tren in water towards Cu(ii) and highly reactive Cu(0) leads to O2-free reaction environments within the first seconds of the reaction, even when the reaction takes place in the open-air. By leveraging this significantly fast O2-reducing activity of the disproportionation reaction, a range of well-defined water-soluble polymers with narrow dispersity are attained in a few minutes or less. This methodology provides the ability to prepare block copolymers via sequential monomer addition with little evidence for chain termination over the lifetime of the polymerization and allows for the synthesis of star-shaped polymers with the use of multi-functional initiators. The mechanism of self-deoxygenation is elucidated with the use of various characterization tools, and the species that participate in the rapid oxygen consumption is identified and discussed in detail.

Aggregation-Induced Emission Active Polyacrylates via Cu-Mediated Reversible Deactivation Radical Polymerization with Bioimaging Applications.

The introduction of aggregation-induced emission (AIE) moieties into polymers results in smart materials with AIE characteristics, expanding their scope of applications. Herein, well-defined polymers with controlled molecular weight, low dispersity, and high end-group fidelity are produced via copper(0)-mediated reversible-deactivation radical polymerizations (Cu(0)-RDRPs). An AIE-containing initiator tetraphenylethene bromoisobutyrate (TPEBIB) has been synthesized, fully characterized, and utilized for the construction of different polyacrylate homopolymers and block copolymers bearing the TPE group with a range of molecular weights and architectures. All of the polymers exhibited AIE behavior. Notably, the hydrophobic TPE-poly(tert-butyl acrylate) (TPE-PtBA)-containing block copolymers are transformed to TPE-poly(acrylic acid) (TPE-PAA)-based amphiphilic copolymers by facile deprotection, enabling pH-tunable self-assembly in aqueous media to give fluorescent nanoparticles with various sizes. The low cytotoxicity, high specificity, and excellent photostability render them promising candidates as lysosome-specific probes in biological imaging applications.

Protein-polymer bioconjugates via a versatile oxygen tolerant photoinduced controlled radical polymerization approach.

The immense application potential of amphiphilic protein-polymer conjugates remains largely unexplored, as established "grafting from" synthetic protocols involve time-consuming, harsh and disruptive deoxygenation methods, while "grafting to" approaches result in low yields. Here we report an oxygen tolerant, photoinduced CRP approach which readily affords quantitative yields of protein-polymer conjugates within 2 h, avoiding damage to the secondary structure of the protein and providing easily accessible means to produce biomacromolecular assemblies. Importantly, our methodology is compatible with multiple proteins (e.g. BSA, HSA, GOx, beta-galactosidase) and monomer classes including acrylates, methacrylates, styrenics and acrylamides. The polymerizations are conveniently conducted in plastic syringes and in the absence of any additives or external deoxygenation procedures using low-organic content media and ppm levels of copper. The robustness of the protocol is further exemplified by its implementation under UV, blue light or even sunlight irradiation as well as in buffer, nanopure, tap or even sea water.