Surface-initiated RAFT Polymerization Research Articles

Solvent effects on surface-grafted and solution-born poly[N-(2-hydroxypropyl)methacrylamide] during surface-initiated RAFT polymerization

Solvent effects influence grafting density and cause discrepancy between molar mass of surface-grafted and solution-born poly[N-(2-hydroxypropyl) methacrylamide] during surface-initiated RAFT polymerization.

Fluoropolymer-MOF Hybrids with Switchable Hydrophilicity for 19F MRI-Monitored Cancer Therapy

Cancer theranostics that combines cancer diagnosis and therapy is a promising approach for personalized cancer treatment. However, current theranostic strategies suffer from low imaging sensitivity for visualization and an inability to target the diseased tissue site with high specificity, thus hindering their translation to the clinic. In this study, we have developed a tumor microenvironment-responsive hybrid theranostic agent by grafting water-soluble, low-fouling fluoropolymers to pH-responsive zeolitic imidazolate framework-8 (ZIF-8) nanoparticles by surface-initiated RAFT polymerization. The conjugation of the fluoropolymers to ZIF-8 nanoparticles not only allows sensitive in vivo visualization of the nanoparticles by 19F MRI but also significantly prolongs their circulation time in the bloodstream, resulting in improved delivery efficiency to tumor tissue. The ZIF-8-fluoropolymer nanoparticles can respond to the acidic tumor microenvironment, leading to progressive degradation of the nanoparticles and release of zinc ions as well as encapsulated anticancer drugs. The zinc ions released from the ZIF-8 can further coordinate to the fluoropolymers to switch the hydrophilicity and reverse the surface charge of the nanoparticles. This transition in hydrophilicity and surface charge of the polymeric coating can reduce the "stealth-like" nature of the agent and enhance specific uptake by cancer cells. Hence, these hybrid nanoparticles represent intelligent theranostics with highly sensitive imaging capability, significantly prolonged blood circulation time, greatly improved accumulation within the tumor tissue, and enhanced anticancer therapeutic efficiency.

Chiral polymer coatings on substrates via surface-initiated RAFT polymerization under ambient conditions

Surface-initiated reversible addition-fragmentation chain transfer polymerization using oxygen (O2-SI-RAFT) was performed to endow the substrates with chiral properties. Chiral monomers were synthesized using methacrylic anhydride and l/d-amino acids (phenylalanine methyl ester, alanine methyl ester, valine methyl ester, and leucine methyl ester), and chiral polymers were grown on titanium and glass substrates. The polymer brushes grafted from the substrates were confirmed by ellipsometry analysis, water contact angles, X-ray photoelectron spectroscopy, and atomic force microscopy. Block copolymer brushes were also polymerized through chain extension. Using a glass substrate, chirality of the polymer brushes grown on the surface could be confirmed via circular dichroism spectroscopy.

Fabrication of pH and thermal dual-responsive hyperbranched copolymer grafted magnetic graphene oxide via surface-initiated RAFT-SCVP for controlled release of DOX

Herein, a novel stimuli-responsive magnetic graphene oxide/hyperbranched copolymer nanocomposites (GO@Fe3O4 @HBC) was prepared via mixing surface-initiated RAFT and self-condensing vinyl polymerization technique. In the first step, chain transfer monomer (CTM) was synthesized by the esterification reaction between 2-(dodecylthiocarbonothioylthio)− 2-methylpropionic acid (DDMAT) and 2-Hydroxyethyl methacrylate (HEMA). Besides, graphene oxide nanosheets were decorated with Fe3O4 nanoparticles. The surface of magnetic graphene oxide nanosheets was modified with 3-amino propyl (trimethoxysilyl) (APTS) and then the DDMAT was anchored to the surface of their nanosheets via amidification reaction. At last, smart hyperbranched poly (NIPAM-co-AA) was effectively grafted to the surface of magnetic graphene oxide using the SI-RAFT-SCVP technique. The chemical and physical structure of the synthesized GO@Fe3O4 @HBC were investigated by FT-IR, H NMR, GPC, TGA, DLS, CHN, VSM, UV-Vis, SEM, EDAX, and TEM. The synthesized GO@Fe3O4 @HBC was used as a nanocarrier. The drug delivery efficacy of this nanocarrier was investigated in terms of in vitro doxorubicin (DOX) release and MTT assay against HeLa cells, which confirms both acidic pH and thermo-sensitive behavior. The MTT assay also revealed that the nanocarrier without DOX was biocompatible having cell viability greater than 90% for HeLa cells. DOX-loaded nanocarrier showed high cytotoxic effect on HeLa Cells.

Multifunctionalization of RC membrane via combining surface initiated RAFT polymerization with thiolactone chemistry for enhanced antibody recovery

Hydrophobic charge induction chromatography (HCIC) is becoming an attractive separation technology for antibody purification but suffers from low recovery. Herein we attempted to incorporate temperature responsiveness and strong ion exchange functions onto HCIC membrane adsorber to enhance antibody recovery. We proposed a multifunctional surface modification method combining surface-initiated reversible addition-fracture chain transfer polymerization (SI-RAFT) and the thiolactone chemistry. A regenerated cellulose (RC) membrane was modified by the SI-RAFT of N-isopropylacrylamide (NIPAAm) and thiolactone acrylamide (TIaAm), followed by the “amine-thiol-ene” cascade reaction of thiolactone with tryptamine, a HCIC ligand and methylpropylene trioxyethyl ammonium chloride (METAC), a strong ion exchanger. Temperature, pH and salt effects on IgG and BSA adsorption were investigated. After optimization, the RC-HCIC membrane adsorber had a static adsorption capacity of 41 mg/g for IgG, and an ideal IgG to BSA separation factor of 4.7, under the condition of pH = 7 and T = 30 °C. The membrane showed temperature-responsive IgG uptake from 10 °C to 35 °C. At pH = 5 and T = 10 °C, the recovery of IgG reached 93.5%, and the activity was well retained. These results indicate that the combination of temperature responsiveness of NIPAAm with HCIC is an effective strategy to improve the IgG recovery.

A novel material poly(N-acryloyl-L-glycine)-brush grafted N-doped magnetic biochar by surface-initiated RAFT polymerization for efficient elimination of heavy metal ions

To remove toxic and non-degradable heavy metal ions, a novel magnetically responsive polymer brush based on eco-friendly biochar was designed and prepared using reversible addition fragmentation chain transfer polymerization method. Subsequently, functional groups, structures, specific surface areas and morphologies of the material were characterized by FT-IR, SEM, BET, Raman and TGA. Then, the material was applied to remove Cr6+ and Cu2+. Additionally, a series of factors that might affect the adsorption were also explored, such as pH, salt concentration, time and temperature. Results concluded that the prepared material with abundant functional groups had excellent adsorption capacity of 34.84 and 112.94 mg/g, respectively for Cr6+ and Cu2+ at 318 K. Finally, characterization results of FT-IR and XPS indicated that adsorption mechanisms were primarily attributed to ion exchange, electrostatic interaction, cation-π bonding and hydrogen bonding. Based on experimental results, prepared material had excellent adsorption capacity, high cycle performance, quick magnetic separation performance, making it as a promising material for sewage treatment.

Surface-initiated reversible addition fragmentation chain transfer of fluoromonomers: an efficient tool to improve interfacial adhesion in piezoelectric composites

Baryum titanate/P(VDF-co-TrFE) piezoelectric composites with sturdy interfaces thanks to surface-initiated RAFT polymerization prepared fluoropolymer brushes.

A Novel Material Poly(N-Acryloyl-L-Glycine)-Brush Grafted N-Doped Magnetic Biochar by Surface-Initiated Raft Polymerization for Efficient Elimination of Heavy Metal Ions

A Novel Material Poly(N-Acryloyl-L-Glycine)-Brush Grafted N-Doped Magnetic Biochar by Surface-Initiated Raft Polymerization for Efficient Elimination of Heavy Metal Ions

Surface initiated RAFT polymerization to synthesize N-heterocyclic block copolymer grafted silica nanofillers for improving PEM properties

Surface functionalization of silica nanoparticles (SiNP) has gained attention as an efficient methodology in improving the properties of the proton exchange membrane (PEM). Here, we report the development of block copolymer grafted SiNP (BC-g-SiNP) as functional nanofiller which was further blended with oxypolybenzimidazole (OPBI) to prepare nanocomposite-based PEM. Block copolymer chains consisting of poly (N-Vinyl imidazole) (pNVI) and poly (N-Vinyl-1,2,4-triazole) (pNVT) were grown on the SiNP surface using grafting-from RAFT polymerization in one pot process. Two series of BC-g-SiNP namely pNVI-b-pNVT-g-SiNP and pNVT-b-pNVI-g-SiNP were synthesized by altering the polymer chain grafting sequence. A series of BC-g-SiNP was developed by varying chain length of each block to understand the effect of the chain sequence and length on the properties of nanofiller and their influence in altering the PEM properties. The block copolymer structure, chain sequence and chain length were confirmed by means of NMR and GPC analysis of the cleaved copolymer chains. The BC-g-SiNP exhibited core-shell morphology and thickness of the shell altered as the chain length and sequence of the grafted chains tuned. Phosphoric acid (PA) loaded OPBI/BC-g-SiNP nanocomposite PEM showed very high thermal, mechanical and chemical stabilities along with the proton conductivity as high as 0.278 S cm-1 at 180 °C in case of OPBI/P6(3%). A very clear-cut dependence of the PEM properties was observed on the architecture of the BC-g-SiNP such as chain length and sequence.

Hollow polymer nanocapsules with a ferrocenyl copolymer shell

Hollow polymer nanocapsules consisting of ferrocenyl shell have been developed by crosslinking the polymer chains grafted over silica nanoparticles synthesized via one pot surface-initiated RAFT polymerization.

Biological Sample-Compatible Ratiometric Fluorescent Molecularly Imprinted Polymer Microspheres by RAFT Coupling Chemistry.

Ratiometric fluorescent molecularly imprinted polymer (MIP) sensors hold great promise in many bioanalytical areas because of their high sensitivity and selectivity as well as excellent self-referencing and visual detection capability. However, their synthetic strategies are rather limited and the development of such optosensing MIPs that can directly and selectively quantify small organic analytes in complex biological samples remains a formidable challenge owing to the complexity of sample matrices. Herein, a versatile and modular strategy to obtaining well-defined ratiometric fluorescent MIP microspheres capable of directly and selectively detecting an organic herbicide [2,4-dichlorophenoxyacetic acid (2,4-D)] in undiluted pure milks is described. First, it involves the synthesis of uniform "living" polymer particles via RAFT precipitation polymerization, their successive well-controlled grafting of a polymer shell labeled with red CdTe QDs (being inert to 2,4-D) and an MIP shell labeled with green 4-nitrobenzo[c][1,2,5]oxadiazole (NBD) units (showing fluorescence "light-up" upon binding 2,4-D) via surface-initiated RAFT polymerization, and final grafting of hydrophilic poly(N-isopropylacrylamide) brushes via an efficient coupling reaction (i.e., RAFT coupling chemistry). The resulting hydrophilic dual fluorescent MIP particles showed excellent photostability and reusability. They exhibited obvious analyte binding-induced "turn-on"-type ratiometric fluorescence (and color) change and high 2,4-D optosensing selectivity and sensitivity in pure bovine milk (with a detection limit of 0.13 μM). Moreover, they were directly applied to 2,4-D determination in undiluted pure goat milk with good recoveries (96.0-103.2%) and high accuracy (RSD = 1.5-5.5%), even in the presence of several analogues of 2,4-D. The general applicability of our strategy was also demonstrated. This study paves the way for efficiently developing various advanced MIP optosensors (of easily tunable structures and desired properties) highly promising in many bioanalytical applications.

Grafting of zwitterion polymer on polyamide nanofiltration membranes via surface-initiated RAFT polymerization with improved antifouling properties as a new strategy

Special radical grafting strategies, e.g. surface-initiated reversible addition-fragmentation chain transfer (SI-RAFT) polymerization, are considered as promising techniques for the purpose of not only uniformly modifying nanofiltration (NF) membranes with the functional polymers but also preventing nonspecific protein adsorption. In this research work, we decide to report for the first time an efficient approach to stabilize RAFT initiators on the surface of polyamide NF membranes and study the effect of the chain length of the polymer on the membrane fouling performance. For this purpose, using interfacial polymerization between trimesoyl chloride (TMC) and a mixture of diamines (i.e. 1,3-phenylenediamine (MPD) and (3,5-diamino phenyl) methanol (DAPM), polyamide thin film composite NF membranes were synthesized. Afterward, the reaction between the polyamide thin film composite layer and α-bromoisobutyryl bromide (BIBB) was carried out. It was found that the stabilized amount of BIBB on the surface of the prepared membranes could be efficiently enhanced by using the DAPM treatment. Finally, using RAFT polymerization technique, a zwitterionic polymer, poly[(2-methacryloyloxy)ethyl]dimethyl[3-sulfopropyl]ammonium hydroxide (pMEDSAH), was successfully grafted on the membrane surface. It is noteworthy that the irreversible adsorption amount of proteins on the prepared pMEDSAH-grafted membrane appreciably decreased to >96%. All the provided results indicate that all the pMEDSAH-grafted membranes, which were prepared using a facile and efficient method, have proved promising for practical applications.

Facile Preparation of Well-Defined Uniform Hydrophilic Hairy Hollow Functional Polymer Micro- and Nanoparticles

A facile, general, and highly efficient strategy for preparing well-defined uniform hydrophilic hairy hollow functional polymer micro- and nanoparticles by combining RAFT polymerization techniques and sacrificial template method is described. Two synthetic routes have been developed for this purpose. The first route involves one-pot synthesis of uniform “living” poly(methacrylic acid) (PMAA) micro/nanospheres with surface-bound dithioester groups via RAFT precipitation polymerization (RAFTPP), their successive grafting of cross-linked functional polymer layers and hydrophilic polymer brushes via surface-initiated RAFT (SI-RAFT) polymerization, and rapid etching of the PMAA core by simply washing the resulting core-shell-corona-structured particles with methanol. Alternatively, such hairy hollow polymer particles can also be prepared by synthesis of uniform “living” hollow polymer particles (through controlled grafting of cross-linked functional polymer layers onto “living” PMAA particles prepared via RAFT...

Imprinting the location of an in-built RAFT agent and selective grafting of polymer chains inside or outside the pores of mesoporous silica nanoparticles

Abstract Mesoporous silica nanoparticles (MSNs) primed with RAFT agent were synthesized via co-condensation of tetraethoxysilane (TEOS) and organoalkoxysilane based RAFT agent. The nature of the R group in organoalkoxysilane based RAFT agent was varied in order to control the preferential location of polymer grafting. Two different RAFT agents were prepared, one RAFT agent contained phenyl ethyl as R group, and other RAFT agent contained isobutyric acid as R group. The stability of the organoalkoxysilane based RAFT agents was confirmed employing UV–Visible spectroscopy and 1H solution NMR spectroscopy techniques. Succeeding this RAFT functionalized MSNs preparation, surface-initiated RAFT polymerization was carried out using N-isopropylacrylamide (NIPAM). RAFT and polymer functionalized MSNs were then characterized by diverse techniques such as FT-IR, TGA, UV–Visible spectroscopy, surface area measurement, X-ray photoelectron spectroscopy (XPS), 13C and 29Si solid-state NMR spectroscopy. The outcome of utilizing different types of organoalkoxysilane based RAFT agent on the morphology was examined using SEM and TEM. Spherical and cuboid shape was observed in the case of RAFT–COOH–MSNs and RAFT-Ph-MSNs respectively. Higher percentage of polymer grafting was observed in case of PNIPAM–COOH–MSNs in comparison to PNIPAM-Ph-MSNs. The realization of preferential grafting of polymer on exterior or interior surface of RAFT MSNs was established using pore size/volume analysis by BET as well as by XPS. The characteristic resonances in 13C and 29Si solid-state NMR and characteristic vibrations in FT-IR, confirms successful synthesis of organic-inorganic hybrids. The analysis of thermoresponsiveness of PNIPAM grafted MSNs was experimented by drug loading and release studies at different temperatures as well as by confocal laser scanning microscopy.

PH and thermal dual-responsive poly(NIPAM-co-GMA)-coated magnetic nanoparticles via surface-initiated RAFT polymerization for controlled drug delivery.

Herein, a novel type of multifunctional magnetic nanoparticles with dual thermal and pH-responsive behavior was fabricated as the carrier for delivery of doxorubicin (DOX). Fe3O4@SiO2 magnetic nanoparticles, were grafted with polymer brushes consisting of poly (NIPAM-co-GMA) (PNG) chains via surface initiated reversible addition-fragmentation chain transfer (SI-RAFT) polymerization. The polymer brushes were then modified with hydrazine groups as DOX binding sites. The prepared multifunctional magnetic nanoparticles were characterized by FT-IR, 1H NMR, XPS, TGA, DLS, VSM, GPC, TEM, and XRD analysis. The in vitro drug release of the multifunctional magnetic nanoparticles was examined at 37 °C (above LCST) and 25 °C (below LCST) in different pH media and exhibited excellent pH- and thermo-sensitive behavior. The results show that the Fe3O4@SiO2@PNG-Hy fabricated via SI-RAFT polymerization is a viable candidate material for tumor treatment studies.

A facile design of smart silica nanocarriers via surface-initiated RAFT polymerization as a dual-stimuli drug release platform

The rational design of hybrid nanostructures with an active core and a modified shell can promote several biological applications. Herein, a coating platform has been developed to obtain monodispersed core-shell magnetic mesoporous silica nanocarriers. The surface of silica shells has been successfully modified by disulfide bonds and the photoresponsive polymer, poly(2-nitrobenzyl acrylate) (PNBA), via RAFT polymerization using azobisisobutyronitrile (AIBN) as a thermal initiator. The results showed that these nanocarriers have nanospherical morphologies with high porosity, large surface areas, and suitable pore volumes. Furthermore, ibuprofen (IBU) as a model drug has been loaded easily into the polymeric nanocontainers with a high loading content, followed by coating with β-Cyclodextrin (β-CD) as effective gatekeeper molecules. Treating these nanocarriers with ultraviolet light causes the photocleavage of o-nitrobenzyl ester moieties contained in the growing polymer chains. The controlled release of the loaded IBU cargo can be achieved by ultraviolet light, or reduction cleavable of the disulfide bond, or both together. Interestingly, the magnetic core can enhance the release process through magnetic guiding and pushing the nanocarriers to the targeted sites by using an external magnet or a directed magnetic field. The prepared photodegradable polymer nanocarriers can be widely applied in the fields of controlled drug delivery systems (DDS) and pharmacologically active polymers.

Effect of two different RAFT reactions on grafting MMA from pre-irradiated PP film

The graft polymerization of methyl methacrylate (MMA) from pre-irradiated polypropylene (PP) films mediated by two different addition-fragmentation chain transfer (RAFT) polymerization mechanisms—surface-initiated RAFT polymerization and interface-mediated RAFT polymerization was studied. In the first mechanism, electron beam irradiation technique was applied to produce the initial radical active sites and peroxides on PP films. 4-cyanopentanoic acid dithiobenzoate (CPADB) was added in the solution to mediate the graft polymerization. In the second mechanism, a new technique utilizing the decomposition and recombination of peroxides produced by electron beam and di(thiobenzoyl) disulfide (DBDS) to anchor CTA on PP films was applied. GPC, ATR-FTIR, XPS, SEM and water contact angle were used to characterize graft layer. Surface-initiated RAFT polymerization was found to be fast and facile with high degree of grafting (Dg) and large number-average molecular weight. But the samples after reaction were swelling and out of shape. Interface-mediated RAFT polymerization led to rather low Dg and low molecular weight. But the samples kept their pristine shapes and had better surface properties.

Fabrication of poly(β-cyclodextrin)-conjugated magnetic graphene oxide by surface-initiated RAFT polymerization for synergetic adsorption of heavy metal ions and organic pollutants

Synergetic adsorption of Cd2+ and SMT was realized on poly(β-cyclodextrin)-conjugated magnetic graphene oxide, which was fabricated by surface-initiated RAFT polymerization.

Priming the pores of mesoporous silica nanoparticles with an in-built RAFT agent for anchoring a thermally responsive polymer

Abstract RAFT mesoporous silica nanoparticles (MSNs) have been synthesized for the first time via co-condensation of an organoalkoxysilane RAFT agent, 1-phenylethyl(3-(triethoxysilyl)propyl)carbonotrithioate, with tetraethoxysilane (TEOS) in aqueous basic cetyltrimethylammonium bromide. The stability of the organoalkoxysilane RAFT agent during the synthesis of MSNs was established using solution NMR and UV–visible spectroscopies. The RAFT-MSNs were then used for elaboration with N-isopropylacrylamide (NIPAM) via controlled surface-initiated RAFT polymerization. The success of the incorporation of the organoalkoxysilane RAFT agent into the silica network, and polymerization of PNIPAM was confirmed with TGA, FT-IR, UV–visible spectroscopy, 13C and 29Si solid state NMR spectroscopy. The effect of the organoalkoxysilane based RAFT agent and PNIPAM grafting on the morphology, size and surface area of the resulting MSNs was investigated using SEM, TEM, XRD, DLS and BET analysis. The appearance of carbon signals in 13C solid state NMR, T signals in 29Si solid state NMR and C H stretching signals in FT-IR establishes that we have successfully obtained organic-inorganic hybrid materials. The pore area calculated using Barrett-Joyner-Halenda (BJH) analysis was 87.8 m2 g−1 for control-MSNs, 91.1 m2 g−1 for RAFT-MSNs and 132.9 m2 g−1 for PNIPAM-MSNs. The thermoresponsive behaviour of PNIPAM grafted inside the pores of MSNs was studied by dye as well as drug loading experiments at variable temperatures, followed by characterization using confocal laser scanning microscopy. The green and red fluorescence corresponding to fluorescein and doxorubicin respectively was strongly retained in the PNIPAM-MSNs after 24 h of incubation at 25 °C while lack of fluorescence after 24 h incubation at 35 °C, demonstrates the thermoresponsive behaviour of the polymer being grafted inside the pores of mesoporous silica nanoparticles.

Surface-initiated RAFT polymerization from vapor-based polymer coatings

Surface-initiated reversible addition-fragmentation chain transfer (SI-RAFT) polymerization was used to synthesize poly(methyl methacrylate) (PMMA) and poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammoniumhydroxide (PMEDSAH) brushes grafted from reactive poly[p-xylylene] surfaces. The synthetic approach involved functionalization of substrates via chemical vapor deposition polymerization of an electron-deficient alkynyl-functionalized [2.2]paracyclophane derivative. An azide-functionalized RAFT agent was anchored to the resulting poly[(p-xylylene-4-methyl propiolate)-co-p-xylylene] films via copper-free click-chemistry. Subsequent SI-RAFT polymerization yielded PMMA and PMEDSAH films with narrow dispersity which was further tuned by varying the concentration of a sacrificial RAFT agent in solution. Polymer dispersity was determined by size exclusion chromatography to be in the range of 1.2–1.4 for both polymers. This work provides a novel surface modification strategy to decorate a wide range of different substrates with polymer brushes, thereby eliminating the need for cumbersome modification protocols, which so far had to be established for each substrate material independently.