Biobased Transesterification Vitrimers.

The rapid increase in the use of plastics and the related sustainability issues, including the depletion of global petroleum reserves, have rightly sparked interest in the use of biobased polymer feedstocks. Thermosets cannot be remolded, processed, or recycled, and hence cannot be reused because of their permanent molecular architecture. Vitrimers have emerged as a novel polymer family capable of bridging the difference between thermoplastic and thermosets. Vitrimers enable unique recycling strategies, however, it is still important to understand where the raw material feedstocks originate from. Transesterification vitrimers derived from renewable resources are a massive opportunity, however, limited research has been conducted in this specific family of vitrimers. This review article provides a comprehensive overview of transesterification vitrimers produced from biobased monomers. The focus is on the biomass structural suitability with dynamic covalent chemistry, as well as the viability of the synthetic methods.

Tunable Electrochemical Peptide Modifications: Unlocking New Levels of Orthogonality for Side-Chain Functionalization.

Electrochemical transformations provide enticing opportunities for programmable, residue-specific peptide modifications. Herein, we harness the potential of amidic side-chains as underutilized handles for late-stage modification through the development of an electroauxiliary-assisted oxidation of glutamine residues within unprotected peptides. Glutamine building blocks bearing electroactive side-chain N,S-acetals are incorporated into peptides using standard Fmoc-SPPS. Anodic oxidation of the electroauxiliary in the presence of diverse alcohol nucleophiles enables the installation of high-value N,O-acetal functionalities. Proof-of-principle for an electrochemical peptide stapling protocol, as well as the functionalization of dynorphin B, an endogenous opioid peptide, demonstrates the applicability of the method to intricate peptide systems. Finally, the site-selective and tunable electrochemical modification of a peptide bearing two discretely oxidizable sites is achieved.

Strong, Self-Healable, and Recyclable Visible-Light-Responsive Hydrogel Actuators.

The most pressing challenges for light-driven hydrogel actuators include reliance on UV light, slow response, poor mechanical properties, and limited functionalities. Now, a supramolecular design strategy is used to address these issues. Key is the use of a benzylimine-functionalized anthracene group, which red-shifts the absorption into the visible region and also stabilizes the supramolecular network through π-π interactions. Acid-ether hydrogen bonds are incorporated for energy dissipation under mechanical deformation and maintaining hydrophilicity of the network. This double-crosslinked supramolecular hydrogel developed via a simple synthesis exhibits a unique combination of high strength, rapid self-healing, and fast visible-light-driven shape morphing both in the wet and dry state. As all of the interactions are dynamic, the design enables the structures to be recycled and reprogrammed into different 3D objects.

Using Synergistic Multiple Dynamic Bonds to Construct Polymers with Engineered Properties.

Dynamic bonds have achieved significant attention for their ability to impart fascinating properties to polymeric materials, such as high mechanical strength, self-healing, shape memory, 3D printability, and conductivity. Incorporating multiple dynamic bonds into polymer systems affords an attractive and efficient approach to endow multiple functionalities. This mini-review focuses on the use of complementary dynamic interactions to control the properties of soft materials. Owing to the diversity in dynamic chemistries that can be explored, the scope of this article is restricted to polymers and does not include colloids, amphiphiles, liquid crystals, or biological soft matter.

Dynamic Covalent Hydrogels for Triggered Cell Capture and Release.

A dual-responsive, cell capture and release surface was prepared through the incorporation of phenylboronic acid (PBA) groups into an oxime-based polyethylene glycol (PEG) hydrogel. Owing to its PEG-like properties, the unfunctionalized hydrogel was nonfouling. The use of highly efficient oxime chemistry allows the incorporation of commercially available 3,5-diformylphenyl boronic acid into the hydrogel matrix. Thus, the surface properties of the hydrogel were modified to enable reversible cell capture and release. Boronic ester formation between PBA groups and cell surface carbohydrates enabled efficient cell capture at pH 6.8. An increase to pH 7.8 resulted in cell detachment. This capture-and-release procedure was performed on MCF-7 human breast cancer cells, NIH-3T3 fibroblast cells, and primary human umbilical vein endothelial cells (HUVECs) and could be cycled with negligible loss in activity. The facile preparation of PBA-functionalized surfaces presented here has applications in biomedical fields such as cell diagnostics and cell culture.

Triggered and Tunable Hydrogen Sulfide Release from Photogenerated Thiobenzaldehydes.

Hydrogen sulfide (H2 S) has been identified as an important cell-signaling mediator and has a number of biological functions, such as vascular smooth muscle relaxation, neurotransmission, and regulation of inflammation. A facile and versatile approach for H2 S production initiated by light irradiation and controlled by reaction with an amine or an amino acid was developed. The donor was synthesized in a one-pot reaction, and simple crystallization led to a yield of approximately 90 %. The synthetic strategy is scalable and versatile, and the H2 S donors can be expressed ina number of different molecular and macromolecular forms, including crystalline small-molecule compounds, water-soluble polymers, polystyrene films, and hydrogels. The H2 S donors based on polystyrene film and hydrogel were used as cell-culture scaffolds. The H2 S donor based on water-soluble polymer was applied in photocontrolled inhibition of P-selectin expression on human platelets and subsequent regulation of platelet aggregation. This study provides the simplest controllable H2 S source to study its biological functions. The developed materials are also new therapeutic platforms to deliver H2 S, as there is no accumulation of toxic byproducts, and the donor materials from polystyrene films and hydrogels can be readily removed after releasing H2 S.

Versatile Synthesis of Amino Acid Functional Polymers without Protection Group Chemistry.

The copolymerization of N-isopropylacrylamide (NiPAm) with aldehyde functional monomers facilitates postpolymerization functionalization with amino acids via reductive amination, negating the need for protecting groups. In reductive amination, the imine formed from the condensation reaction between an amine and an aldehyde is reduced to an amine. In this work, we categorize amino acids into four classes based on the functionality of their side chains (acidic, polar neutral, neutral, and basic) and use their amine groups in condensation reactions with aldehyde functional polymers. The dynamic nature of the imine as well as the versatility of reductive amination to functionalize a polymer with a range of amino acids is highlighted. In this manner, amino acid functional polymers are synthesized without the use of protecting groups with high yields, demonstrating the high functional group tolerance of carbonyl condensation chemistry and the subsequent reduction of the imine. Prior to the reduction of the imine bond, transimination reactions are used to demonstrate dynamic polymers that shuffle from a glycine- to a histidine-functional polymer.

Doubly Dynamic Self-Healing Materials Based on Oxime Click Chemistry and Boronic Acids.

The dynamic covalent characteristics of oxime and boronate ester bonds have been explored. A small excess of a competing aldehyde under acidic conditions resulted in oxime polymer degradation from high molecular weights (30 kDa) to low molecular weight oligomers (2.2 kDa). The dynamic nature of oxime bonds imparts oxime cross-linked hydrogels with self-healing properties and the incorporation of phenyl boronic acid groups into the hydrogel network provides a platform for hydrogel functionalization. The addition of a polyphenol (tannic acid) proves a facile means to incorporate a second, dynamic covalent cross-linking network through boronate ester formation which, owing to the increase in the degree of cross-linking, is found to be nearly double the hydrogel strength (storage modulus increased from 4.6 to 8.5 kPa). Finally, the tannic acid cross-linking network is selectively degraded returning the hydrogel storage modulus to its initial value and providing a means for the synthesis of materials with tunable mechanical properties.

Manipulation of Molecular Weight Distribution Shape as a New Strategy to Control Processing Parameters.

Molecular weight and dispersity (Ð) influence physical and rheological properties of polymers, which are of significant importance in polymer processing technologies. However, these parameters provide only partial information about the precise composition of polymers, which is reflected by the shape and symmetry of molecular weight distribution (MWD). In this work, the effect of MWD symmetry on thermal and rheological properties of polymers with identical molecular weights and Ð is demonstrated. Remarkably, when the MWD is skewed to higher molecular weight, a higher glass transition temperature (Tg ), increased stiffness, increased thermal stability, and higher apparent viscosities are observed. These observed differences are attributed to the chain length composition of the polymers, easily controlled by the synthetic strategy. This work demonstrates a versatile approach to engineer the properties of polymers using controlled synthesis to skew the shape of MWD.

A Versatile and Scalable Strategy to Discrete Oligomers.

A versatile strategy is reported for the multigram synthesis of discrete oligomers from commercially available monomer families, e.g., acrylates, styrenics, and siloxanes. Central to this strategy is the identification of reproducible procedures for the separation of oligomer mixtures using automated flash chromatography systems with the effectiveness of this approach demonstrated through the multigram preparation of discrete oligomer libraries (D = 1.0). Synthetic availability, coupled with accurate structural control, allows these functional building blocks to be harnessed for both fundamental studies as well as targeted technological applications.

Xanthate-Functional Temperature-Responsive Polymers: Effect on Lower Critical Solution Temperature Behavior and Affinity toward Sulfide Surfaces.

Xanthate-functional polymers represent an exciting opportunity to provide temperature-responsive materials with the ability to selectively attach to specific metals, while also modifying the lower critical solution temperature (LCST) behavior. To investigate this, random copolymers of poly(N-isopropylacrylamide) (PNIPAM) with xanthate incorporations ranging from 2 to 32% were prepared via free radical polymerization. Functionalization with 2% xanthate increased the LCST by 5 °C relative to the same polymer without xanthate. With increasing xanthate composition, the transition temperature increased and the transition range broadened until a critical composition of the hydrophilic xanthate groups (≥18%) where the transition disappeared completely. The adsorption of the polymers at room temperature onto chalcopyrite (CuFeS2) surfaces increased with xanthate composition, while adsorption onto quartz (SiO2) was negligible. These findings demonstrate the affinity of these functional smart polymers toward copper iron sulfide relative to quartz surfaces, presumably due to the interactions between xanthate and specific metal centers.

A facile synthesis of dynamic, shape-changing polymer particles.

We herein report a new facile strategy to ellipsoidal block copolymer nanoparticles that exhibit a pH-triggered anistropic swelling profile. In a first step, elongated particles with an axially stacked lamellae structure are selectively prepared by utilizing functional surfactants to control the phase separation of symmetric polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) in dispersed droplets. In a second step, the dynamic shape change is realized by cross-linking the P2VP domains, thereby connecting glassy PS discs with pH-sensitive hydrogel actuators.

Polymers from Cellulosic Waste: Direct Polymerization of Levoglucosenone using DBU as a Catalyst.

The bio-based platform molecule levoglucosenone (LGO) is now produced at multi-ton scale by the pyrolysis of cellulosic waste. As such it has become an industrially viable, non-petroleum-derived chemical feedstock. Herein we report the direct (one-step) and operationally simple polymerization of LGO that provides a highly sustainable method for polymer synthesis. Specifically, the ability of LGO to act as an electrophile has been harnessed so as to deliver high molecular weight polymers (Mn=236,000 g/mol, D=2.4) possessing excellent thermal stabilities (TD5 %=249 °C). Furthermore, there is a significant capacity for the effective chemical manipulation of these polymers as exemplified by treatment of them under Baeyer-Villiger conditions and so creating a simple and green route to hydrophilic materials. These one- and two-step transformations provide the most direct route to new, LGO-derived polymer scaffolds yet reported. E-factors of ca. 0.012 and atom economies of up to 99 % have been realized.

Nanoparticle PET/CT imaging of natriuretic peptide clearance receptor in prostate cancer.

Atrial natriuretic peptide has been recently discovered to have anticancer effects via interaction with cell surface natriuretic peptide receptor A (NPRA) and natriuretic peptide clearance receptor (NPRC). In a preclinical model, NPRA expression has been identified during tumor angiogenesis and may serve as a potential prognostic marker and target for prostate cancer (PCa) therapy. However, the presence of NPRC receptor in the PCa model has not yet been assessed. Furthermore, there is still no report using nanoparticle for PCa positron emission tomography (PET) imaging. Herein, an amphiphilic comb-like nanoparticle was synthesized with controlled properties through modular construction containing C-atrial natriuretic factor (CANF) for NPRC receptor targeting and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) chelator for high specific activity Cu-64 radiolabeling. The pharmacokinetics of (64)Cu-CANF-Comb exhibited tuned biodistribution and optimized in vivo profile in contrast to the nontargeted (64)Cu-Comb nanoparticle. PET imaging with (64)Cu-CANF-Comb in CWR22 PCa tumor model showed high blood pool retention, low renal clearance, enhanced tumor uptake, and decreased hepatic burden relative to the nontargeted (64)Cu-Comb. Immunohistochemistry staining confirmed the presence of NPRC receptor in tumor tissue. Competitive PET receptor blocking study demonstrated the targeting specificity of (64)Cu-CANF-Comb to NPRC receptor in vivo. These results establish a new nanoagent for prostate cancer PET imaging.

Fine-Tuning Electroauxiliary-Mediated Peptide Modifications Using Second-Generation Electroactive Amino Acids.

Arylthioether functional groups serve as effective electroauxiliaries for tunable oxidations. Herein, we disclose the synthesis of second-generation glutamine building blocks bearing 2,4-dimethoxythiophenyl and 2,4-dichlorothiophenyl-derived electroauxiliaries. These building blocks improve SPPS efficiency and enable fine-tuning of the electrochemical window for selective anodic oxidation reactions in comparison to first-generation 4-methoxythiophenyl- and 4-nitrothiophenyl-substituted variants. Installation onto a segment of involucrin, a protein component of human skin, emphasizes the practical application of the new building blocks for iterative functionalizations.

Reactive, multifunctional polymer films through thermal cross-linking of orthogonal click groups.

The ability to produce robust and functional cross-linked materials from soluble and processable organic polymers is dependent upon facile chemistries for both reinforcing the structure through cross-linking and for subsequent decoration with active functional groups. Generally, covalent cross-linking of polymeric assemblies is brought about by the application of heat or light to generate highly reactive groups from stable precursors placed along the chains that undergo coupling or grafting reactions. Typically, these strategies suffer from a general lack of control of the cross-linking chemistry as well as the fleeting nature of the reactive species that precludes secondary chemistry. We have addressed both of these issues using orthogonal chemistries to effect both cross-linking and subsequent functionalization of polymer films by mild heating, which results in exacting control of the cross-link density as well as the density of the residual stable functional groups available for subsequent, stepwise functionalization. This methodology is exploited to develop a strategy for the independent and orthogonal triple-functionalization of cross-linked polymer thin-films through microcontact printing.

Precise synthesis of molecularly defined oligomers and polymers by orthogonal iterative divergent/convergent approaches.

The synthesis of perfectly defined (macro)molecules has been a constant challenge for polymer and organic chemists. This paper highlights the main applications of the iterative divergent/convergent approach for the synthesis of discrete mass oligomers and polymers. We will discuss the orthogonal deprotection and coupling strategies involved in this powerful strategy where chain length doubles at each iteration and which has been applied to the synthesis of conjugated rigid rods as well as amorphous and crystalline oligomers and polymers. The synthesis of perfectly defined oligomers in respect to emerging highly efficient and orthogonal chemistries will also be highlighted.

Exploiting Nature's Most Abundant Polymers: Developing New Pathways for the Conversion of Cellulose, Hemicellulose, Lignin and Chitin into Platform Molecules (and Beyond).

The four most prominent forms of biomass are cellulose, hemicellulose, lignin and chitin. In efforts to develop sustainable sources of platform molecules there has been an increasing focus on examining how these biopolymers could be exploited as feedstocks that support the chemical supply chain, including in the production of fine chemicals. Many different approaches are possible and some of the ones being developed in the authors' laboratories are emphasised.

Photochromic, metal-absorbing honeycomb structures.

We demonstrate the synthesis and use of a spiropyran functional polymer to form highly ordered honeycomb materials by the breath figure technique, which is based on the self-assembly of water droplets. These materials undergo rapid and intense color changes both in solution and as porous films by irradiation with light (UV or visible). We also demonstrate the metal binding ability of these polymers ultimately to create hybrid organic-inorganic porous structures. Furthermore, by reduction of the metal and calcination of the organic materials, unique palladium microrings can be prepared. The methods described are general techniques that may be applied to a range of heavy metals.

Extrusion 3D Printing of Polymeric Materials with Advanced Properties.

3D printing is a rapidly growing technology that has an enormous potential to impact a wide range of industries such as engineering, art, education, medicine, and aerospace. The flexibility in design provided by this technique offers many opportunities for manufacturing sophisticated 3D devices. The most widely utilized method is an extrusion-based solid-freeform fabrication approach, which is an extremely attractive additive manufacturing technology in both academic and industrial research communities. This method is versatile, with the ability to print a range of dimensions, multimaterial, and multifunctional 3D structures. It is also a very affordable technique in prototyping. However, the lack of variety in printable polymers with advanced material properties becomes the main bottleneck in further development of this technology. Herein, a comprehensive review is provided, focusing on material design strategies to achieve or enhance the 3D printability of a range of polymers including thermoplastics, thermosets, hydrogels, and other polymers by extrusion techniques. Moreover, diverse advanced properties exhibited by such printed polymers, such as mechanical strength, conductance, self-healing, as well as other integrated properties are highlighted. Lastly, the stimuli responsiveness of the 3D printed polymeric materials including shape morphing, degradability, and color changing is also discussed.