Photoinduced Controlled/Living Polymerizations.

The application of photochemistry in polymer synthesis is of interest due to the unique possibilities offered compared to thermochemistry, including topological and temporal control, rapid polymerization, sustainable low-energy processes, and environmentally benign features leading to established and emerging applications in adhesives, coatings, adaptive manufacturing, etc. In particular, the utilization of photochemistry in controlled/living polymerizations often offers the capability for precise control over the macromolecular structure and chain length in addition to the associated advantages of photochemistry. Herein, the latest developments in photocontrolled living radical and cationic polymerizations and their combinations for application in polymer syntheses are discussed. This Review summarizes and highlights recent studies in the emerging area of photoinduced controlled/living polymerizations. A discussion of mechanistic details highlights differences as well as parallels between different systems for different polymerization methods and monomer applicability.

Block Copolymers Based on Ethylene and Methacrylates Using a Combination of Catalytic Chain Transfer Polymerisation (CCTP) and Radical Polymerisation.

Two scalable polymerisation methods are used in combination for the synthesis of ethylene and methacrylate block copolymers. ω-Unsaturated methacrylic oligomers (MMAn ) produced by catalytic chain transfer (co)polymerisation (CCTP) of methyl methacrylate (MMA) and methacrylic acid (MAA) are used as reagents in the radical polymerisation of ethylene (E) in dimethyl carbonate solvent under relatively mild conditions (80 bar, 70 °C). Kinetic measurements and analyses of the produced copolymers by size exclusion chromatography (SEC) and a combination of nuclear magnetic resonance (NMR) techniques indicate that MMAn is involved in a degradative chain transfer process resulting in the formation of (MMA)n -b-PE block copolymers. Molecular modelling performed by DFT supports the overall reactivity scheme and observed selectivities. The effect of MMAn molar mass and composition is also studied. The block copolymers were characterised by differential scanning calorimetry (DSC) and their bulk behaviour studied by SAXS/WAXS analysis.

Self-healing and mechanical performance of dynamic glycol chitosan hydrogel nanocomposites.

The application of functional self-healing and mechanically robust hydrogels in bioengineering, drug delivery, soft robotics, etc., is continuously growing. However, fabricating hydrogels that simultaneously possess good mechanical and self-healing properties remains a challenge. Developing robust hydrogel formulations for the encapsulation and release of hydrophobic substances is a major challenge especially in some pharmaceutical treatments where the many of drugs show incompatibility with the hydrophilic hydrogel matrices. Schiff base hydrogels have been developed using a benzaldehyde multifunctional amphiphilic polyacrylamide crosslinker in conjunction with glycol chitosan. The polymeric crosslinker was synthesized by a two-step reaction using aqueous Cu-RDRP to give an ABA telechelic copolymer of N,N-dimethyl acrylamide (DMAc) and N-hydroxyethyl acrylamide (HEAm) from a bifunctional PEG. The polymer was then modified by post functionalization leading to a multifunctional benzaldehyde crosslinker that was shown to be capable of self-assembly into aggregates in aqueous media serving as a possible candidate for the entrapment of hydrophobic substances. Aqueous solutions of the crosslinker spontaneously formed hydrogels when mixed with glycol chitosan due to the in situ formation of imine bonds. Hydrogels were characterized while additional comparisons were made with a commonly used bifunctional PEG crosslinker. The effect of introducing partially reduced graphene oxide (GO) nanosheets was also examined and led to enhancements in both mechanical properties (2.0 fold increase in modulus and 1.4 fold increase in strain) and self-healing efficiencies (>99% from 60% by rheology) relative to the pristine polymer hydrogels.

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.

Tandem Mass Spectrometry for Polymeric Structure Analysis: A Comparison of Two Common MALDI-ToF/ToF Techniques.

Tandem mass spectrometry is a powerful technique for investigating polymer architecture. However, in-depth studies of the technique for polymers is relatively lacking when compared to other areas of mass spectrometry (MS). This paper examines the use laser-induced dissociation and collision-induced dissociation (CID) in MALDI-LIFT-ToF/ToF experiments to compare the usage of the two techniques on a range of polymeric analytes. It is demonstrated that for samples with an energetically preferable fragmentation pathway, such as those with a functional group in the backbone or a labile end group, post source decay (PSD) provides a simplified spectra with an increased pathway selectivity due to its utilization of metastable decay. This makes PSD a preferable technique for polymer sequencing, especially in low-resolution time-of-flight techniques. Conversely, CID fragments less selectively, leading to higher intensity peaks from less favorable fragmentations. This makes CID more preferred for exact structural determination, such as finding the repeat unit structure.

Polymers for Fluorescence Imaging of Formaldehyde in Living Systems via the Hantzsch Reaction.

Formaldehyde (FA) has been detected via the Hantzsch reaction for many decades. However, the Hantzsch reaction has been rarely used to detect FA in biological systems due to the disadvantages of small-molecule probes (including toxicity and poor water solubility). In this study, polymeric fluorescent probes were developed to resolve these issues associated with small molecules, and FA in living systems was successfully detected via the Hantzsch reaction. These water-soluble polymers were easily scaled-up (∼25 g) by radical polymerization using commercial monomers. These polymers exhibited similar, albeit better, sensitivity to FA compared to water-soluble small molecules, primarily indicative of the advantages of polymers for the detection of FA via the Hantzsch reaction. The polymer structures were highly biocompatible with the probes; thus, these polymers can effectively detect endogenous FA in cells or zebrafish in a safe manner. This result confirmed the superiority of polymers in safety as biocompatible materials. This study highlights a straightforward method for exploring probes for the detection of FA in living systems. It offers functional polymers for bioimaging and extends the application scope of the Hantzsch reaction, reflecting the utility of a broad study of organic reactions in interdisciplinary fields as well as possible key implications in organic chemistry, analytical chemistry, and polymer chemistry.

Sequence-controlled methacrylic multiblock copolymers via sulfur-free RAFT emulsion polymerization.

Translating the precise monomer sequence control achieved in nature over macromolecular structure (for example, DNA) to whole synthetic systems has been limited due to the lack of efficient synthetic methodologies. So far, chemists have only been able to synthesize monomer sequence-controlled macromolecules by means of complex, time-consuming and iterative chemical strategies such as solid-state Merrifield-type approaches or molecularly dissolved solution-phase systems. Here, we report a rapid and quantitative synthesis of sequence-controlled multiblock polymers in discrete stable nanoscale compartments via an emulsion polymerization approach in which a vinyl-terminated macromolecule is used as an efficient chain-transfer agent. This approach is environmentally friendly, fully translatable to industry and thus represents a significant advance in the development of complex macromolecule synthesis, where a high level of molecular precision or monomer sequence control confers potential for molecular targeting, recognition and biocatalysis, as well as molecular information storage.