Atom Transfer Radical Polymerization: A Robust and Versatile Route for Polymer Synthesis

Self-assembled block copolymer biomaterials for oral delivery of protein therapeutics

Protein therapeutics have guided a transformation in disease treatment for various clinical conditions. They have been successful in numerous applications, but administration of protein therapeutics has been limited to parenteral routes which can decrease patient compliance as they are invasive and painful. In recent years, the synergistic relationship of novel biomaterials with modern protein therapeutics has been crucial in the treatment of diseases that were once thought of as incurable. This has guided the development of a variety of alternative administration routes, but the oral delivery of therapeutics remains one of the most desirable due to its ease of administration. This review addresses important aspects of micellar structures prepared by self-assembled processes with applications for oral delivery. These two characteristics have not been placed together in previous literature within the field. Therefore, we describe the barriers for delivery of protein therapeutics, and we concentrate in the oral/transmucosal pathway where drug carriers must overcome several chemical, physical, and biological barriers to achieve a successful therapeutic effect. We critically discuss recent research on biomaterials systems for delivering such therapeutics with an emphasis on self-assembled synthetic block copolymers. Polymerization methods and nanoparticle preparation techniques are similarly analyzed as well as relevant work in this area. Based on our own and others' research, we analyze the use of block copolymers as therapeutic carriers and their promise in treating a variety of diseases, with emphasis on self-assembled micelles for the next generation of oral protein therapeutic systems.

Rapid RAFT Polymerization of Acrylamide with High Conversion

Rapid RAFT polymerization can significantly improve production efficiency of PAM with designed molecular structure. This study shows that ideal Reversible Addition–Fragmentation Chain Transfer (RAFT) polymerization of acrylamide is achieved in dimethyl sulfoxide (DMSO) solution at 70 °C. The key to success is the appropriate choice of both a suitable RAFT chain transfer agent (CTA) and initiating species. It is illustrated that dodecyl trithiodimethyl propionic acid (DMPA) is a suitable trithiocarbonate RAFT CTA and is synthesized more easily than other CTAs. Compared to other RAFT processes of polymers, the reaction system shortens reaction time, enhances conversion, and bears all the characteristics of a controlled radical polymerization. The calculation result shows that high concentrations can reduce high conversions, accelerate the reaction rate, and widen molecular weight distributions slightly. This work proposes an excellent approach for rapid synthesis of PAMs with a restricted molecular weight distribution.

Recent Advances in the Application of ATRP in the Synthesis of Drug Delivery Systems

Advances in atom transfer radical polymerization (ATRP) have enabled the precise design and preparation of nanostructured polymeric materials for a variety of biomedical applications. This paper briefly summarizes recent developments in the synthesis of bio-therapeutics for drug delivery based on linear and branched block copolymers and bioconjugates using ATRP, which have been tested in drug delivery systems (DDSs) over the past decade. An important trend is the rapid development of a number of smart DDSs that can release bioactive materials in response to certain external stimuli, either physical (e.g., light, ultrasound, or temperature) or chemical factors (e.g., changes in pH values and/or environmental redox potential). The use of ATRPs in the synthesis of polymeric bioconjugates containing drugs, proteins, and nucleic acids, as well as systems applied in combination therapies, has also received considerable attention.

Photoredox Catalysis in Photocontrolled Cationic Polymerizations of Vinyl Ethers

ConspectusAdvances in photocontrolled polymerizations have expanded the scope of polymer architectures and structures that can be synthesized for various applications. The majority of these polymerizations have been developed for radical processes, which limits the diversity of monomers that can be used in macromolecular design. More recent developments of photocontrolled cationic polymerizations have taken a step toward addressing this limitation and have expanded the palette of monomers that can be used in stimuli-regulated polymerizations, enabling the synthesis of previously inaccessible polymeric structures. This Account will detail our group's studies on cationic polymerization processes where chain growth is regulated by light and highlight how these methods can be combined with other stimuli-controlled polymerizations to precisely dictate macromolecular structure.Photoinitiated cationic polymerizations are well-studied and important processes that have control over initiation. However, we wanted to develop systems where we had spatiotemporal control over both polymer initiation and chain growth. This additional command over the reaction provides the ability to manipulate the growing polymer with an external stimulus during a polymerization, which can be used to control structure. To achieve this goal, we set out to develop a method to photoreversibly generate a cation at a growing chain end that could participate in a controlled polymerization process. We took inspiration from previous work on cationic degenerate chain transfer polymerizations of vinyl ethers that used thiocarbonylthio chain transfer agents. These polymerizations were initiated by a strong acid and gave well-defined poly(vinyl ether)s. We posited that we could remove the acid initiator in these systems and reversibly oxidize the thiocarbonylthio chain ends in these reactions with a photocatalyst to give a photocontrolled cationic polymerization of vinyl ethers. This Account will focus on our journey to discover cationic photocontrolled polymerizations. We will summarize our initial developments and detail our mechanistic understanding of these reactions using both organic and inorganic based photocatalysts, and we will outline more recent efforts to expand cationic degenerate chain transfer polymerizations to other thioacetal initiators. Finally, we will detail how these photocontrolled cationic polymerizations can be used to switch monomer selectivity in situ using light to control polymer structure. At the end of the Account, we will discuss our vision for future potential applications of these photocontrolled cationic polymerizations in the synthesis of novel block copolymers and next generation cross-linked networks.

Synthesis of block copolymers used in polymersome fabrication: Application in drug delivery

Amphiphilic block copolymers are common materials used for the fabrication of various nanostructures with biomedical applications including nanocapsules, nanospheres, micelles and polymeric vesicles. According to the literature, polymersomes have several advantages compared to other nanostructures used as drug delivery systems comprising better stability, facile synthesis, prolonged circulation time, and passive/active targeting capability. Various types of nanoparticles are formed by varying the ratio of the hydrophobic/hydrophilic blocks. Changing hydrophobic/hydrophilic ratio of amphiphilic block copolymers has an impact on the structural characteristics of polymers such as changing molecular weight and surface functionalization of the block copolymer. Thus, polymerization strategies are an important factor that influences polymersomes quality. In this review, different polymerization strategies for the synthesis of block copolymers applied in polymersomes formation, are described.

Enhancing antifouling property of PVA membrane by grafting zwitterionic polymer via SI-ATRP method

Poly(zwitterions) polymer brushes were fabricated by surface-initiated atom transfer radical polymerization (SI-ATRP) on PVA substrate. The results of XPS and FTIR proved the successful graft of CBMA and SBMA to PVA. The surface of the PVA films would be rougher after the functionalization. Its hydrophilicity increased dramatically and the water contact angle decreased from 45.2° to 7.2°. The visible light transmittance was above 88%. Mechanical properties decreased slightly after grafting, the tensile strength and tensile strain at break were in 1.23-1.85 MPa and 361.7-471.1%, respectively. The anti-protein adsorption performance of the modified PVA film was significantly enhanced and the lowest adsorption amount was up to 2.25 μg/cm². The cytotoxicity grade of modified PVA film was 0-1, which indicated the modified film possessed no cytotoxicity. Additionally, the surface of zwitterion-grafted PVA film had strongly resistance to cell adhesion. All the results confirmed that the zwitterions modified PVA was a promising anti-fouling material for the further biomedical use.

Glycan-Directed Grafting-from Polymerization of Immunoglobulin G: Site-Selectively Modified IgG-Polymer Conjugates with Preserved Biological Activity

Antibody and related antibody drugs for the treatment of malignancies have led to progress in targeted cancer therapy. Preparation of diverse antibody conjugates is critical for preclinical and clinical applications. However, precise control in tagging molecules at specific locations on antibodies is essential to preserve their native function. In this study, a synthetic boronic acid (BA)-tosyl initiator was used to trigger a glycan-directed modification of IgGs, and the obtained IgG macroinitiators allowed a growth of the poly N-isopropylacrylamide (PNIPAAm) chains specifically at Fc-domains. Therefore, the PNIPAAm chains are located away from the critical antigen-binding domains (Fab), which could reasonably prevent the loss of biological activity after the attachment of polymer chains. According to the proposed strategy, a site-selectively modified anticoncanavalin A (Con A) antibody-PNIPAAm conjugate showed 6-times higher efficiency in the binding of targeted Con A antigen to a randomly conjugated anti-Con A antibody-PNIPAAm conjugate. In this study, we developed the first chemical strategy for the site-specific preparation of IgG-polymer conjugates with conserved biological activity as well as intact glycan structures.

Mechanism of Supplemental Activator and Reducing Agent Atom Transfer Radical Polymerization Mediated by Inorganic Sulfites: Experimental Measurements and Kinetic Simulations

The mechanism of atom transfer radical polymerization (ATRP) mediated by sodium dithionite (Na2S2O4), with CuIIBr2/Me6TREN as catalyst (Me6TREN: tris[2-(dimethylamino)ethyl]amine)) in ethanol/water mixtures, was investigated experimentally and by kinetic simulations. A kinetic model was proposed and the rate coefficients of the relevant reactions were measured. The kinetic model was validated by the agreement between experimental and simulated results. The results indicated that the polymerization followed the SARA ATRP mechanism, with a SO2•- radical anion derived from Na2S2O4, acting as both supplemental activator (SA) of alkyl halides and reducing agent (RA) for CuII/L to regenerate the main activator CuI/L. This is similar to the reversible-deactivation radical polymerization (RDRP) procedure conducted in the presence of Cu0. The electron transfer from SO2•-, to either CuIIBr2/Me6TREN or R-Br initiator, appears to follow an outer sphere electron transfer (OSET) process. The developed kinetic model was used to study the influence of targeted degree of polymerization, concentration of CuIIBr2/Me6TREN and solubility of Na2S2O4 on the level of polymerization control. The presence of small amounts of water in the polymerization mixtures slightly increased the reactivity of the CuI/L complex, but markedly increased the reactivity of sulfites.

Convenient syntheses of fullerynes for 'clicking' into fullerene polymers

Alkyne-functionalized fullerenes (fullerynes) were designed and conveniently synthesized via Bingel reaction in one step with high yields. They were used to react with azido-functionalized polystyrene (PS) via Huisgen [3 + 2] cycloaddition 'click' chemistry to form two fullerene polymers: one with C60 tethered to the end of a PS chain (C60-1PS) and the other with C60 tethered at the junction point of two PS chains of identical molecular weight (C60-2PS). The fullerene polymers were characterized by 1H NMR, 13C NMR, FT-IR, MALDI-TOF mass spectrometry and SEC. The results showed that the fullerene polymers are well-defined with narrow polydispersity and high fullerene functionality. Besides, aggregation of C60 in THF was observed in the SEC traces. The optical properties of the fullerene polymers were studied by UV-Vis absorption spectroscopy, and the results suggested that the PS chain(s) on the fullerene core has no remarkable effect on the optic property of C60. The thermal properties of the fullerene polymers were studied by TGA and DSC, and the results indicated that the two fullerene polymers with different C60 content and distinct molecular topology may have different self-assemble architectures in the solid state. The well-defined fullerene polymers can be used as model compounds to study the self-assemble architecture of shape amphiphiles based on polymer-tethered molecular nanoparticles.

A silver bullet: elemental silver as an efficient reducing agent for atom transfer radical polymerization of acrylates

Elemental silver was used as a reducing agent in the atom transfer radical polymerization (ATRP) of acrylates. Silver wire, in conjunction with a CuBr(2)/TPMA catalyst, enabled the controlled, rapid preparation of polyacrylates with dispersity values down to Đ = 1.03. The silver wire in these reactions was reused several times in sequential reactions without a decline in performance, and the amount of copper catalyst used was reduced to 10 ppm without a large decrease in control. A poly(n-butyl acrylate)-block-poly(tert-butyl acrylate) diblock copolymer was synthesized with a molecular weight of 91 400 and Đ = 1.04, demonstrating good retention of chain-end functionality and a high degree of livingness in this ATRP system.

Preparation of complex multiblock copolymers via aqueous RAFT polymerization at room temperature

Room temperature RAFT polymerisation for the design of multiblock acrylate/acrylamide copolymers.

Thermoresponsive hydrophobic copolymer brushes modified porous monolithic silica for high-resolution bioseparation

Thermoresponsive-hydrophobic copolymer brushes were prepared on porous monolithic silica rods through surface initiated ATRP. The monolithic silica can separate biomolecules with high resolution and in short analysis times.

Synthesis of the first poly(diaminosulfide)s and an investigation of their applications as drug delivery vehicles

This paper reports the first examples of poly(diaminosulfide)s that were synthesized by the reaction of a sulfur transfer reagent and several secondary diamines. The diaminosulfide group has the general structure of R(2)N-S-NR(2) and, although it has been used in the synthesis of small molecules, it has never been utilized in the synthesis of macromolecules until this report. A series of poly(diaminosulfide)s were synthesized at elevated temperatures, and the molecular weights of the polymers were as high as 12,400 g mol(-1) with conversions for the polymerization reaction up to 99%. The rate constants for the transamination reactions that lead to the polymers were measured in several solvents to provide an understanding the reaction conditions necessary to polymerize the monomers. The degradation of diaminosulfides were studied in D(2)O, C(6)D(6), CD(3)OD, CDCl(3), and DMSO-d(6)/D(2)O to demonstrate that they were very stable in organic solvents but degraded within hours under aqueous conditions. These results clearly demonstrated that diaminosulfides are very stable in organic solvents under ambient conditions. Poly(diaminosulfide)s have sufficient stabilities to be useful for many applications. The ability of these polymers to function as drug delivery vehicles were studied by the fabrication of nanoparticles of a water-insoluble poly(diaminosulfide) with a dye. The microparticles were readily absorbed into human embryonic 293 cells and possessed no measureable toxicity towards these same cells.