Living Radical Polymerization Immobilized on Wang Resins: Synthesis and Harvest of Narrow Polydispersity Poly(methacrylate)s

Preparation of Biomolecule-Polymer Conjugates by Grafting-From Using ATRP, RAFT, or ROMP

Biomolecule-polymer conjugates are constructs that take advantage of the functional or otherwise beneficial traits inherent to biomolecules and combine them with synthetic polymers possessing specially tailored properties. The rapid development of novel biomolecule-polymer conjugates based on proteins, peptides, or nucleic acids has ushered in a variety of unique materials, which exhibit functional attributes including thermo-responsiveness, exceptional stability, and specialized specificity. Key to the synthesis of new biomolecule-polymer hybrids is the use of controlled polymerization techniques coupled with either grafting-from, grafting-to, or grafting-through methodology, each of which exhibit distinct advantages and/or disadvantages. In this review, we present recent progress in the development of biomolecule-polymer conjugates with a focus on works that have detailed the use of grafting-from methods employing ATRP, RAFT, or ROMP.

Transition Metal Mediated Living Radical Polymerisation

Living radical polymerisation has witnessed an unprecedented interest from polymer and materials scientists. Traditionally, polymers tended to replace natural materials such as wood, cotton and glass, and were used primarily for their structural features and performance and cost advantages. New functional polymers are essential for the manufacture of cell phones, lap-top computers, new cosmetics, and many pharmaceuticals. It is important to be able to control how monomers are put together within the macromolecule for the design at the molecular level for specific applications. Living polymerisation allows for end group control, polymer chain length and relatively narrow polydispersity polymers. In nature, the ability to control monomer distribution and chain length is obvious with approximately 20 amino acids being the monomers for polymers as diverse as hair, insulin and haemoglobin. Living radical polymerisation solves many of the problems in the use of monomers that contain heteroatoms and functional groups. These tend to be reactive towards strong nucleophiles and electrophiles which are required in ionic polymerisation. Protecting group chemistry as used in small molecule organic synthesis is not practical in polymer synthesis. Thus radicals that are inert to most functional groups and in particular protic species seem to be the answer. The mechanism of the transition metal mediate systems is extremely complicated with a range of organometallic species present in the reaction mixture. Solvents and coordinating monomers drastically affect the ideal reaction conditions and it is impossible to predict the optimum conditions for each synthesis without certain experiments being carried out. Nevertheless, catalyst systems are available which are acceptable and work well enough to be able to make a plethora of different macromolecules for a diverse range of applications /properties.

Preparation of functionalized star polymer nanoparticles by RAFT polymerization and their application in positionally assembled enzymes for cascade reactions

A novel multienzyme nanoreactor with excellent substrate affinity – functionalized star polymer nanoparticles was prepared by RAFT polymerization as a scaffold.

Nano-Star-Shaped Polymers for Drug Delivery Applications

With the advancement of polymer engineering, complex star-shaped polymer architectures can be synthesized with ease, bringing about a host of unique properties and applications. The polymer arms can be functionalized with different chemical groups to fine-tune the response behavior or be endowed with targeting ligands or stimuli responsive moieties to control its physicochemical behavior and self-organization in solution. Rheological properties of these solutions can be modulated, which also facilitates the control of the diffusion of the drug from these star-based nanocarriers. However, these star-shaped polymers designed for drug delivery are still in a very early stage of development. Due to the sheer diversity of macromolecules that can take on the star architectures and the various combinations of functional groups that can be cross-linked together, there remain many structure-property relationships which have yet to be fully established. This review aims to provide an introductory perspective on the basic synthetic methods of star-shaped polymers, the properties which can be controlled by the unique architecture, and also recent advances in drug delivery applications related to these star candidates.

Surface-Initiated Controlled Radical Polymerization: State-of-the-Art, Opportunities, and Challenges in Surface and Interface Engineering with Polymer Brushes

The generation of polymer brushes by surface-initiated controlled radical polymerization (SI-CRP) techniques has become a powerful approach to tailor the chemical and physical properties of interfaces and has given rise to great advances in surface and interface engineering. Polymer brushes are defined as thin polymer films in which the individual polymer chains are tethered by one chain end to a solid interface. Significant advances have been made over the past years in the field of polymer brushes. This includes novel developments in SI-CRP, as well as the emergence of novel applications such as catalysis, electronics, nanomaterial synthesis and biosensing. Additionally, polymer brushes prepared via SI-CRP have been utilized to modify the surface of novel substrates such as natural fibers, polymer nanofibers, mesoporous materials, graphene, viruses and protein nanoparticles. The last years have also seen exciting advances in the chemical and physical characterization of polymer brushes, as well as an ever increasing set of computational and simulation tools that allow understanding and predictions of these surface-grafted polymer architectures. The aim of this contribution is to provide a comprehensive review that critically assesses recent advances in the field and highlights the opportunities and challenges for future work.

Star Polymers

Recent advances in controlled/living polymerization techniques and highly efficient coupling chemistries have enabled the facile synthesis of complex polymer architectures with controlled dimensions and functionality. As an example, star polymers consist of many linear polymers fused at a central point with a large number of chain end functionalities. Owing to this exclusive structure, star polymers exhibit some remarkable characteristics and properties unattainable by simple linear polymers. Hence, they constitute a unique class of technologically important nanomaterials that have been utilized or are currently under audition for many applications in life sciences and nanotechnologies. This article first provides a comprehensive summary of synthetic strategies towards star polymers, then reviews the latest developments in the synthesis and characterization methods of star macromolecules, and lastly outlines emerging applications and current commercial use of star-shaped polymers. The aim of this work is to promote star polymer research, generate new avenues of scientific investigation, and provide contemporary perspectives on chemical innovation that may expedite the commercialization of new star nanomaterials. We envision in the not-too-distant future star polymers will play an increasingly important role in materials science and nanotechnology in both academic and industrial settings.

Recent Progress on Transition Metal Catalyst Separation and Recycling in ATRP

Atom transfer radical polymerization (ATRP) is a versatile and robust tool to synthesize a wide spectrum of monomers with various designable structures. However, it usually needs large amounts of transition metal as the catalyst to mediate the equilibrium between the dormant and propagating species. Unfortunately, the catalyst residue may contaminate or color the resultant polymers, which limits its application, especially in biomedical and electronic materials. How to efficiently and economically remove or reduce the catalyst residue from its products is a challenging and encouraging task. Herein, recent advances in catalyst separation and recycling are highlighted with a focus on (1) highly active ppm level transition metal or metal free catalyzed ATRP; (2) post-purification method; (3) various soluble, insoluble, immobilized/soluble, and reversible supported catalyst systems; and (4) liquid-liquid biphasic catalyzed systems, especially thermo-regulated catalysis systems.

Templated polymerizations on solid supports mediated by complementary nucleoside interactions

The preparation of immobilized poly(methacryloyl nucleosides) and their abilities for template polymerizations is discussed.

Polymer-peptide block copolymers - an overview and assessment of synthesis methods

Incorporating peptide blocks into block copolymers opens up new realms of bioactive or smart materials. Because there are such a variety of peptides, polymers, and hybrid architectures that can be imagined, there are many different routes available for the synthesis of these chimera molecules. This review summarizes the contemporary strategies in combining synthesis techniques to create well-defined peptide-polymer hybrids that retain the vital aspects of each disparate block. Living polymerization can be united with the molecular-level control afforded by peptide blocks to yield block copolymers that not only have precisely defined primary structures, but that also interact with other (bio)molecules in a well defined manner.

Synthesis of novel size exclusion chromatography support by surface initiated aqueous atom transfer radical polymerization

We report the use of aqueous surface-initiated atom transfer radical polymerization (SI-ATRP) to grow polymer brushes from a "gigaporous" polymeric chromatography support for use as a novel size exclusion chromatography medium. Poly(N,N-dimethylacrylamide) (PDMA) was grown from hydrolyzable surface initiators via SI-ATRP catalyzed by 1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA)/CuCl. Grafted polymer was characterized semiquantitatively by ATR-FTIR and also cleaved and quantitatively characterized for mass, molecular weight, and polydispersity via analytical SEC/MALLS. The synthesis provides control over graft density and allows the creation of dense brushes. Incorporation of negative surface charge was found to be crucial for improving the initiation efficiency. As polymer molecular weight and density could be controlled through reaction conditions, the resulting low-polydispersity grafted polymer brush medium is shown to be suitable for use as a customizable size exclusion chromatography medium for investigating the principals of entropic interaction chromatography. All packed media investigated showed size-dependent partitioning of solutes, even for low graft density systems. Increasing the molecular weight of the grafts allowed solutes more access to the volume fraction in the column available for partitioning. Compared to low graft density media, increased graft density caused eluted solute probes to be retained less within the column and allowed for greater size discrimination of probes whose molecular weights were less than 10(4) kDa.

Synthesis of azide/alkyne-terminal polymers and application for surface functionalisation through a [2 + 3] Huisgen cycloaddition process, "click chemistry"

Living radical polymerization of methyl methacrylate (MMA) and a fluorescent comonomer with 2-bromo-2-methylpropionic acid 3-azidopropyl ester and 2-bromo-2-methylhept-6-yn-3-one as initiators has been successfully employed for the synthesis of fluorescently tagged azide and alkyne terminated PMMA with close to that predicted, PDI < 1.20, and good first order kinetics as expected for a living polymerisation. Cotton and organic resin surfaces have been functionalised with alkyne groups using a condensation with 4-chlorocarbonylbutyric acid prop-2-ynyl ester. The surfaces have been further modified using a Huisgen [2 + 3] cycloaddition ("click") reaction of polymeric and small molecule azides. Different functional azides, mono azido-PEG and a new fluorescent hostasol derivative have been prepared and tested as model substrates for cotton surface modification. FTIR, tensiometry, FE-SEM and confocal spectroscopy have been used to characterize the modified surfaces. Tensiometry shows an increase in the hydrophobicity of the surface; verified by FE-SEM which shows a change in surface morphology. The use of the fluorescence label allows fluorescent and confocal microscopy to demonstrate the surface reactions. This approach is shown to be very general allowing soft and hard surfaces with different geometries to be modified. In particular it is an excellent method to alter the nature of organic resins allowing the incorporation of many different functionalities.

Bioinspired functional block copolymers

The diversity and complexity of structures and functions in synthetic polymer systems can be increased through conjugation with biological segments or, in other words, through generation of "polymer-bioconjugates" or "macromolecular chimeras". The present contribution highlights major synthetic approaches toward sophisticated functional hybrid block copolymers and analyses of structure-function relationships.

Recent advances in shell cross-linked micelles

The field of shell cross-linked (SCL) micelles is briefly reviewed. Important advances over the last two years are emphasized, potential application areas are discussed and current technical problems with these fascinating nanoparticles are highlighted. Particular attention is paid to (i) the development of new cross-linking chemistries and (ii) the adsorption of SCL micelles at interfaces.

Well-defined azlactone-functionalized (co)polymers on a solid support: synthesis via supported living radical polymerization and application as nucleophile scavengers

Wang resin has been converted to a supported initiator for transition metal-mediated living radical polymerization often called atom-transfer radical polymerization (ATRP) of 2-vinyl-4,4-dimethyl-5-oxazolone (VDM) and styrene (S). Several "Rasta" resins with well-defined macromolecular architectures, including homopolymers PVDM, PS, statistical P(S-stat-VDM), block P(S-b-VDM), and P[S-b-(S-stat-VDM)] copolymers, have been elaborated. For the homopolymerization of VDM and S, a sacrificial initiator, benzyl 2-bromoisobutyrate (BBI), has been introduced to monitor the evolution of molar masses and polydispersity indexes (PDIs) of PS and PVDM onto the Wang resin support without cleavage. After 6 h, 86.7% conversion of VDM is reached, with the isolated PVDM chains having a molar mass of 18 000 g mol(-1) and a PDI value of 1.22. Block copolymers have been synthesized in two steps, involving the synthesis of the PS block isolated at low conversions (<15%) to maintain the bromine end-chain functionality and the subsequent synthesis of the second PVDM or P(S-stat-VDM) block. Polydispersity indexes of the cleaved (co)polymers were low (PDI = 1.11-1.44), and high azlactone loadings have been reached (loading = 6.0 mmol g(-1)). Such azlactone-functionalized Wang resins have shown high efficiency during the scavenging process of benzylamine as monitored by HPLC. Moreover, grafted statistical copolymers have shown the best behavior for removing benzylamine because of an improvement of the accessibility of azlactone rings by the dilution with styrene units.

Merging Organic and Polymer Chemistries to Create Glycomaterials for Glycomics Applications

[Image: see text] Oligosaccharides at cell surfaces are known to play a critical role in many biological processes such as biorecognition, interactions between cells and with artificial surfaces, immune response, infection and inflammation. In order to facilitate studies of the role of sugars, an increasing number of novel tools are becoming available. New synthetic strategies now provide much more efficient access to complex carbohydrates or glycoconjugates. Branched carbohydrates and hybrids of carbohydrates conjugated to polymers have been prepared using solution and/or solid-phase synthesis and advanced methods of polymerization. These materials are essential for the development of methodologies to study and map the molecular structure-function relationship at interfaces. This article highlights recent advances in the synthesis of carbohydrates and polymer hybrids mimicking the properties and functionalities of the natural oligosaccharides, as well as selected applications in biology, biotechnology and diagnostics.