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An Exciting Time for Polymer Chemists in Australia

2019; Wiley; Volume: 57; Issue: 18 Linguagem: Inglês

10.1002/pola.29488

1099-0518

Cyrille Boyer, Greg G. Qiao,

Electron and X-Ray Spectroscopy Techniques

Over the last 50 years, Australian researchers have made significant contributions to polymer science. Australian scientists have participated in the discovery of many polymerization techniques such as nitroxide-mediated polymerization (NMP), addition-fragmentation polymerization (AFT), and the well-known Reversible Addition-Fragmentation Chain Transfer polymerization (RAFT), as well as the successful commercialization of products utilizing polymers, most notably the plastic banknote. These contributions have been led by the Australian scientists working at the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and Australian universities. Despite previous attempts by other reserve banks in different countries, the Reserve Bank of Australia introduced the first plastic banknote developed by the CSIRO in collaboration with Note Printing Australia. These polymer banknotes are unique in that they utilise biaxially oriented polypropylene (BOPP) and have various security features not implementable in paper banknotes, such as the use of metameric inks. Due to their longevity and low cost of production and replacement, these plastic banknotes have now been adopted by many countries including Brunei, Canada, Maldives, Mauritania, New Zealand, Papua New Guinea, Romania, and Vietnam. Several more countries are in the process of adopting this technology: the United Kingdom, Nigeria, Cape Verde, Chile, The Gambia, Nicaragua, Trinidad and Tobago, Mexico, Botswana, São Tomé and Príncipe, North Macedonia, the Russian Federation, Armenia, Solomon Islands, Egypt, the Organisation of Eastern Caribbean States (OECS), and Samoa. Other successful Australian developments in the field of polymer science have been for contact lenses as well as conductive polymers. These successful commercial products have enabled the development of a strong polymer community in Australia whose work ranges from polymer synthesis to polymer physics. In addition to these commercial successes, Australians have made significant contributions to polymer science at the academic level. RAFT, discovered by Drs Enzo Rizardo, San Thang, and Graeme Moad, has steadily emerged as one of the most versatile techniques for the control of polymer architectures and the number of research articles and patents using RAFT is rapidly increasing. RAFT polymerization is commonly employed for the preparation of functional polymers for bioapplications as well as nanotechnology. These discoveries have made a significant impact in the polymer community as well as in our society. In this special issue, we offer a snapshot of the current polymer research in Australia through 17 articles. As expected, RAFT polymerization will feature prominently. However, other techniques, such as iodine transfer polymerization, are also discussed. Hawker (a native Australian researcher from Brisbane) and co-workers have investigated the use of reversible iodine transfer polymerization for the preparation of polyacrylic acid.1 In this work, the authors have shown the direct polymerization of acrylic acid in water in the presence of sodium iodine; the in situ synthesis of alkyl iodide provides a facile and cheap route to the production of an important commodity polymer (poly(acrylic acid)). Under the impulsion of Hawker and other researchers, photochemistry has re-emerged as a powerful tool for the preparation of functional materials in the last five years. Pu and co-workers2 have summarized in a highlight the current strategies for the preparation of photoactive chitosan and its application for the preparation of biomaterials. In a research article, Pu and his team have applied photopolymerization for the preparation of hydroxyapatite nanocomposite hydrogels with enhanced cell adhesion.3 By the incorporation of hydroxyapatite, polyvinyl alcohol hydrogels with enhanced mechanical properties were achieved. Junkers and co-workers4 have combined the RAFT process with photopolymerization to precisely grow polymer brushes from silicon wafers. The authors have shown that a film thickness of 25 nm could be prepared in less than 30 minutes. Boyer, Xu, and co-workers5 report the implementation of the photo-mediated single unit monomer insertion (photo-SUMI) methodology in flow. Originally pioneered by Dr Graeme Moad, photo-SUMI utilises a photocatalyst to mediate precise addition of monomers into the polymer chain. The implementation in flow affords both rapid and scaled up preparation of these sequence-defined polymers. Qiao and co-workers6 have proposed the use of the Fenton reaction for the slow initiation of RAFT enabling the synthesis of ultra-high molecular weight polymers up to 20 × 106 g/mol. Such high molecular weight is unprecedented. Konkolewicz (an expatriate Australian researcher from Sydney) and co-workers7 have elegantly utilised light to mediate a thiol-alkene coupling reaction in the presence of Ir(ppy)3 photocatalyst and alkyl halide compounds under blue light. The efficiency and kinetics of these reactions were correlated with the type of alkyl halide present, where ethyl bromoisobutyrate provides the fastest reaction kinetics. These photomediated thiol-ene reactions were successfully applied for the preparation of step-growth polymers and crosslinked networks. Using an alternative form of click-chemistry, Truong and co-workers8 have prepared hydrogels by thiol-halide crosslinking coupling. In addition to providing a fast way to prepare hydrogels, the biocompatibility of the process enabled encapsulation of living cells with negligible effect on cell viability. Heterogeneous polymerization has been and continues to be an important research focus in Australia, where several research groups are developing new heterogeneous processes as well as utilizing these nanoparticles for applications ranging from coatings and adhesives to sophisticated bioapplications. Zetterlund and co-workers9 exploit the compartmentalization effects present in miniemulsion for the preparation of RAFT-derived chains that exhibit significantly increased livingness. Thickett and co-workers10 report the preparation of stabilized nano-objects by way of polymerization-induced self-assembly. Various morphologies were elegantly crosslinked by way of alkoxysilane condensation. These nanoparticles, whose shapes extend beyond the typical spherical shape, are promising for potential application in drug delivery and regenerative medicine. Monteiro's team11 has utilised polymer nanoworms for the preparation of three-dimensional hydrogels. The surface of the nanoworms were decorated with the integrin-binding peptide (RGD) using a novel physical adsorption process that enabled the resulting gels to be successfully immobilised and maintain the viability of human embryonic stem cells. Cameron and co-workers12 offer an alternative strategy to create polymer scaffolds for the 3D culture of human pluripotent stem cells. Cameron's team has polymerized the continuous phase of emulsion to yield highly porous polymers via thiol-acrylate photopolymerization. One of the growing applications of the nanoparticles is their use as drug and imaging agent carriers. Stenzel and co-workers13 have elegantly developed polymer nanoparticles containing fluorine atoms. These nanoparticles can be used as 19F magnetic resonance imaging (MRI) contrast agents. A novel monomer, 2,2,2-trifluoroethylamide l-arginine methacrylamide, was prepared and copolymerised to yield amphiphilic block copolymers, which can self-assemble in water to yield micelles. Quinn, Davis, and co-workers14 have utilised polymer nanoparticles for the delivery of hydrogen sulphide. The authors report a post-modification approach utilising glycidyl functionalities as targets to form macromolecular hydrogen sulphide donors. According to the shape of the nanoparticles, different release profiles of hydrogen sulphide were observed. Connal and co-workers15 have proposed an innovative approach for the reversible self-assembly of block copolymers in the presence of copper (Cu2+) in solution using copper coordinated crosslinking. Due to the rising emergence of antibiotic resistance bacteria, Australian researchers are investigating the potential use of antimicrobial polymers. Peng, Whittaker, and co-workers16 have investigated the potential of polymers containing anilinium groups. In this study, the properties of poly(N,N-dimethylaminophenylene methacrylamide) in solution and as coatings have been investigated against gram-positive and -negative bacteria. These polymers present very broad biocidal properties, with minimal cytotoxicity to human red blood cells. Finally, Müllner's team17 at Sydney University has demonstrated the self-assembly of polystryene-block-poly(2-vinylpyridine) block copolymers as a polymer template for the preparation of mesoporous, nanocrystalline titanium oxide films (anatase samples). These films were applied as electrodes for lithium-ion battery cells. More importantly, in comparison to commercial anatase samples with similar crystallite sizes, the structured materials showed significant performance improvements in terms of capacity, stability, and rate capability. As illustrated in the laudable articles collected in this special edition, polymer chemistry in Australia is strong and diverse with emerging leaders. It is an exciting time for polymer chemists in Australia.