Synthesis and kinetics of graft polymerization of methyl methacrylate from the RAFT coordinated surface of nano-TiO2

Biocompatible Polymer-Grafted TiO2 Nanoparticle Sonosensitizers Prepared Using Phosphonic Acid-Functionalized RAFT Agent

Sonodynamic therapy is widely used in clinical studies including cancer therapy. The development of sonosensitizers is important for enhancing the generation of reactive oxygen species (ROS) under sonication. Herein, we have developed poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC)-modified TiO₂ nanoparticles as new biocompatible sonosensitizers with high colloidal stability under physiological conditions. To fabricate biocompatible sonosensitizers, a grafting-to approach was adopted with phosphonic-acid-functionalized PMPC, which was prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC) using a newly designed water-soluble RAFT agent possessing a phosphonic acid group. The phosphonic acid group can conjugate with the OH groups on the TiO₂ nanoparticles. We have clarified that the phosphonic acid end group is more crucial for creating colloidally stable PMPC-modified TiO₂ nanoparticles under physiological conditions than carboxylic-acid-functionalized PMPC-modified ones. Furthermore, the enhanced generation of singlet oxygen (¹O₂), an ROS, in the presence of PMPC-modified TiO₂ nanoparticles was confirmed using a ¹O₂-reactive fluorescent probe. We believe that the PMPC-modified TiO₂ nanoparticles prepared herein have potential utility as novel biocompatible sonosensitizers for cancer therapy.

Polymer-functionalization of carbon nanotube by in situ conventional and controlled radical polymerizations

Functionalization of carbon nanotube (CNT) with polymers has drawn much attention due to its wide range of applications. Polymer-functionalized CNT could exhibit variety of properties, such as responsivity to environmental stimuli, ability of complexation with metal ions, increased dispersibility in different solvents, higher compatibility with polymer matrix, etc. Chemical and physical methods have been developed for the preparation of polymer-functionalized CNT. Polymer chains are chemically bonded to the CNT edge or surface in the chemical methods, which results in highly stable CNT/polymer composites. "Grafting to", "grafting from", and "grafting through" methods are the most common chemical methods for polymer-functionalization of CNT. In "grafting to" method, pre-fabricated polymer chains are coupled with the either functionalized or non-functionalized CNT. In "grafting from" and "grafting through" methods, CNT is functionalized by polymers simultaneously synthesized by in situ polymerization methods. Conventional free radical polymerization (FRP) and also controlled radical polymerization (CRP) are the most promising methods for in situ tethering of polymer brushes onto the surface of CNT due to their control over the grafting density, thickness, and functionality of the polymer brushes. The main focus of this review is on the synthesis of polymer-functionalized CNT via both the "grafting from" and "grafting through" methods on the basis of FRP and CRP routs, which is commonly known as in situ polymerizations. Finally, the most important challenges and applications of the in situ polymer grafting methods are discussed, which could be interesting for the future works.

Recent Advances in the Synthesis of Polymer-Grafted Low-K and High-K Nanoparticles for Dielectric and Electronic Applications

The synthesis of polymer-grafted nanoparticles (PGNPs) or hairy nanoparticles (HNPs) by tethering of polymer chains to the surface of nanoparticles is an important technique to obtain nanostructured hybrid materials that have been widely used in the formulation of advanced polymer nanocomposites. Ceramic-based polymer nanocomposites integrate key attributes of polymer and ceramic nanomaterial to improve the dielectric properties such as breakdown strength, energy density and dielectric loss. This review describes the "grafting from" and "grafting to" approaches commonly adopted to graft polymer chains on NPs pertaining to nano-dielectrics. The article also covers various surface initiated controlled radical polymerization techniques, along with templated approaches for grafting of polymer chains onto SiO2, TiO2, BaTiO3, and Al2O3 nanomaterials. As a look towards applications, an outlook on high-performance polymer nanocomposite capacitors for the design of high energy density pulsed power thin-film capacitors is also presented.

Preparation of novel multi-walled carbon nanotubes nanocomposite adsorbent via RAFT technique for the adsorption of toxic copper ions

In the present work, polymer-coated multiwalled carbon nanotube (MWCNT) was prepared via RAFT method. First, a novel trithiocarbonate-based RAFT agent was prepared attached chemically into the surface of MWCNT. In addition, the RAFT co-polymerization of acrylic acid and acrylamide monomers was conducted through the prepared RAFT agent. In the next age, the surface morphology and chemical properties of the prepared components were fully examined by using FTIR, ¹HNMR, SEM, TEM, XRD and TGA/DTG techniques. Finally, the modified MWCNT composite was employed as an excellent adsorbent for the adsorption of copper (II) ions. The results indicated that ion adsorption basically relies on adsorbing time, solution pH, initial copper concentration, and adsorbent dosage. Further, the adsorption kinetics and isotherm analysis demonstrated that the adsorption mode was fitted with the pseudo-second-order and Langmuir isotherm models, respectively. Based on the results of thermodynamic study, the ion adsorption process was endothermic and spontaneous. Finally, based on the experimental results, the surface functionalized MWCNT with hydrophilic groups could be successfully used as a promising selective adsorbent material in wastewater treatment.

Synthesis of magnetic functionalized MWCNT nanocomposite through surface RAFT co-polymerization of acrylic acid and N-isopropyl acrylamide for removal of cationic dyes from aqueous solutions

In this study, magnetic multi-walled carbon nanotube (MMWCNT) composites were prepared via surface reversible addition fragmentation chain transfer (RAFT) co-polymerization of acrylic acid (AA) and N-isopropyl acrylamide (NIPAM) in the presence of Fe₃O₄ nanoparticles. First, a novel RAFT agent (RA) was prepared and then immobilized onto the surface of MWCNT to fabricate RA-g-MWCNT. Then, Fe₃O₄ nanoparticles were attached onto the surface of RA-g-MWCNT. Finally, RAFT co-polymerization of AA and NIPAM monomers was carried out via Fe₃O₄-g-RA-g-MWCNT RAFT agent. The structure and morphology of the prepared polymer-coated MWCNT was examined by FTIR, SEM, TEM, XRD, VSM, and TGA. The adsorption behaviours of the cationic dyes were studied. The equilibrium isotherm and kinetics of cationic dyes were investigated. Thermodynamics investigations also depicted that the adsorptions of cationic dyes were spontaneous and endothermic in nature. The synthesized dye adsorbent with high adsorption capacities, reusability, and easy recovery makes it as a good candidate for wastewater treatment.

Effects of RAFT Agent on the Chloromethylstyrene Polymerizations in a Simultaneous Radiation Grafting System

Reversible addition-fragmentation chain transfer (RAFT) agent was added into a simultaneous radiation grafting system and its effects on graft polymerization and homopolymerization were investigated. Chloromethylstyrene (CMS) was graft polymerized onto ethylene-tetrafluoroethylene copolymer (ETFE) films under γ-ray sources via simultaneous irradiation. The non-grafted poly(CMS) in the grafted films were extracted by xylene at 120 °C. The poly(CMS) was characterized by NMR and GPC instruments. Addition of the RAFT agent suppressed both graft polymerization and homopolymerization. However, under a high concentration of RAFT agent, the homopolymerization in the monomer solution could occur through a typical RAFT polymerization while polymerization in the ETFE films proceeded via RAFT and conventional radical polymerization, resulting in poly(CMS) in the ETFE films with molecular weight dispersity higher than 1.0 but lower than that without RAFT agent. Furthermore, it was found that the molecular weight of the poly(CMS) in the ETFE films was several times higher than that of the poly(CMS) in the monomer solution.

Angiogenic Rg1 /Sr-Doped TiO2 Nanowire/Poly(Propylene Fumarate) Bone Cement Composites

A new approach is provided for preparing radiopaque and angiogenic poly(propylene fumarate) (PPF) bone cements by integrating Sr-doped n-TiO₂ nanowires and ginsenoside Rg1 suitable for treating osteonecrosis. High aspect ratio radiopaque TiO₂ -nanowires are synthesized by strontium doping in supercritical CO₂ for the first time, showing a new phase, SrTiO₃ . PPF is synthesized using a transesterification method by reacting diethyl fumarate and propylene glycol, then functionalized using maleic anhydride to produce terminal carboxyl groups, which are subsequently linked to the nanowires. The strong interfacial adhesion between functionalized PPF and nanowires is examined by scanning electron microscopy, Fourier transform infrared, X-ray photoelectron spectroscopy, thermal analysis, and mechanical testing. An angiogenic modulator, ginsenoside Rg₁ , is integrated into the bone cement formulation with the mechanical properties, radiopacity, drug release, and angiogenesis behavior of the formed composites explored. The results show superior radiopacity and excellent release of ginsenoside Rg₁ in vitro, as well as a dose-dependent increase in the branching point numbers. The present study suggests this new methodology provides sufficient mechanical properties, radiopacity, and angiogenic activity to be suitable for cementation of necrotic bone.

Grafting titanium nitride surfaces with sodium styrene sulfonate thin films

The importance of titanium nitride lies in its high hardness and its remarkable resistance to wear and corrosion, which has led to its use as a coating for the heads of hip prostheses, dental implants and dental surgery tools. However, the usefulness of titanium nitride coatings for biomedical applications could be significantly enhanced by modifying their surface with a bioactive polymer film. The main focus of the present work was to graft a bioactive poly(sodium styrene sulfonate) (pNaSS) thin film from titanium nitride surfaces via a two-step procedure: first modifying the surface with 3-methacryloxypropyltrimethoxysilane (MPS) and then grafting the pNaSS film from the MPS modified titanium through free radical polymerization. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were used after each step to characterize success and completeness of each reaction. The surface region of the titanium nitride prior to MPS functionalization and NaSS grafting contained a mixture of titanium nitride, oxy-nitride, oxide species as well as adventitious surface contaminants. After MPS functionalization, Si was detected by XPS, and characteristic MPS fragments were detected by ToF-SIMS. After NaSS grafting, Na and S were detected by XPS and characteristic NaSS fragments were detected by ToF-SIMS. The XPS determined thicknesses of the MPS and NaSS overlayers were ∼1.5 and ∼1.7 nm, respectively. The pNaSS film density was estimated by the toluidine blue colorimetric assay to be 260 ± 70 ng/cm(2).

Synthesis and characterization of novel TiO2-poly(propylene fumarate) nanocomposites for bone cementation

A novel composite material made from poly(propylene fumarate) (PPF) and titania nanofibers has been synthesized for potential use as an orthopaedic biomaterial with TiO₂ nanofibers chemically linked to the PPF matrix as a reinforcing phase to enhance its mechanical properties.

Coating and dispersion of ceramic nanoparticles by UV-ozone etching assisted surface-initiated living radical polymerization

Commercially available unmodified ceramic nanoparticles (NPs) in dry powder state were surface-modified and dispersed in almost single-crystal size. The surface-initiated living radical polymerization after just UV-ozone soft etching enables one to graft polymers onto the surface of ceramic NPs and disperse them in solvents. Furthermore, a number of NPs were dispersed with single-crystal sizes. The technique developed here could be applied to almost all ceramic NPs including metal nitrides.

End-Grafted Polymer Chains onto Inorganic Nano-Objects

Organic/inorganic nanohybrid materials have attracted particular scientific and technological interest because they combine the properties of the organic and the inorganic component. Inorganic nanoparticles exhibit interesting electrical, optical, magnetic and/or catalytic properties, which are related with their nano-scale dimensions. However, their high surface-to-volume ratio often induces agglomeration and leads to the loss of their attractive properties. Surface modification of the inorganic nano-objects with physically or chemically end-tethered polymer chains has been employed to overcome this problem. Covalent tethered polymer chains are realized by three different approaches: the “grafting to”, the “grafting from” and the “grafting through” method. This article reviews the synthesis of end-grafted polymer chains onto inorganic nanoparticles using “controlled/living” polymerization techniques, which allow control over the polymer characteristics and the grafting density of the end-tethered polymer chains.

Grafting of poly(acrylic acid) onto an aluminum surface

Grafting of poly(acrylic acid) (PAA) onto an aluminum surface was successfully achieved by free radical polymerization of acrylic acid using typical radical initiators, benzoyl peroxide and 2,2'-azobisisobutyronitrile. Both spotlike and brush morphologies were achieved. A complete coverage of PAA on an aluminum surface was then achieved by using a thermal chemical vapor deposition process. The PAA thickness was determined by ellipsometry and the superficial chemical composition by X-ray photoelectron spectroscopy (XPS). Grazing angle Fourier transform infrared (FTIR) spectroscopy confirmed the presence of carboxylic acid groups on the surface, and the contact angle measurements revealed a decreasing free surface energy of aluminum due to the polymer surface covering.

Living Radical Polymerization by the RAFT Process - A Second Update

This paper provides a second update to the review of reversible deactivation radical polymerization achieved with thiocarbonylthio compounds (ZC(=S)SR) by a mechanism of reversible addition–fragmentation chain transfer (RAFT) that was published in June 2005 (Aust. J. Chem. 2005, 58, 379–410). The first update was published in November 2006 (Aust. J. Chem. 2006, 59, 669–692). This review cites over 500 papers that appeared during the period mid-2006 to mid-2009 covering various aspects of RAFT polymerization ranging from reagent synthesis and properties, kinetics and mechanism of polymerization, novel polymer syntheses and a diverse range of applications. Significant developments have occurred, particularly in the areas of novel RAFT agents, techniques for end-group removal and transformation, the production of micro/nanoparticles and modified surfaces, and biopolymer conjugates both for therapeutic and diagnostic applications.