Molecularly imprinted polymers by reversible addition-fragmentation chain transfer precipitation polymerization for preconcentration of atrazine in food matrices

Controlled/living free radical polymerization (CLRP) has been accepted as an effective technique in preparation of polymers because of its inherent advantages over traditional free radical polymerization. In this work, reversible addition-fragmentation chain transfer (RAFT) polymerization, the ideal candidate for CLRP, was applied to prepare atrazine molecularly imprinted polymers (MIPs) by precipitation polymerization. The resultant RAFT-MIPs demonstrated uniform spherical shape with rough surface containing significant amounts of micropores, leading to an improvement in imprinting efficiency compared with that of the MIPs prepared by traditional precipitation polymerization (TR-MIPs). The maximum binding capacities of the RAFT-MIPs and TR-MIPs were 2.89 mg g⁻¹ and 1.53 mg g⁻¹, respectively. The recoveries ranging from 81.5% to 100.9% were achieved by one-step extraction by using RAFT-MIPs for preconcentration and selective separation of atrazine in spiked lettuce and corn samples. These results provided the possibility for the separation and enrichment of atrazine from complicated matrices by RAFT-MIPs.     

Enrofloxacin-imprinted monolithic columns synthesized using reversible addition-fragmentation chain transfer polymerization

Molecularly imprinted monolithic columns for selective separation of enrofloxacin were prepared by Reversible Addition-Fragmentation Chain Transfer (RAFT)-mediated radical polymerization. Different ratios of initiation system were used in the synthesis. The structures of the monoliths were characterized to study the relationship between the synthetic conditions and morphology of the monolithic material. The separation performance of the monoliths was evaluated by liquid chromatography. Under optimized synthetic conditions, a monolithic molecularly imprinted polymer (MIP) with high selectivity and improved column efficiency was obtained. The research has shown that RAFT polymerization provides more adjustable conditions for making monolithic materials with different morphologies. The results also demonstrated that homogeneous macro-pore size distribution and large specific surface area are the key factors providing good separation ability and column efficiency for MIP monolithic structures.     

Grafting of molecularly imprinted polymers from the surface of silica gel particles via reversible addition-fragmentation chain transfer polymerization: A selective sorbent for theophylline

Molecularly imprinted polymers (MIPs) were grafted successfully from the surface of silica gel particles via surface initiated reversible addition-fragmentation chain transfer (RAFT) polymerization using RAFT agent functionalized silica gel as the chain transfer agent. The intrinsic characteristics of the controlled/living polymerization mechanism of RAFT allowed for the effective control of the grafting process. Thus the grafting copolymerization of methacrylic acid and divinyl benzene in the presence of template theophylline led to thin MIP film coating silica gel (MIP-Silica). The thickness of MIP film prepared in this study is about 1.98 nm, which was calculated from the nitrogen sorption analysis results. Measured binding kinetics for theophylline to the MIP-Silica and MIPs prepared by conventional bulk polymerization demonstrated that MIP-Silica had improved mass-transfer properties. In addition, the theophylline-imprinted MIP-Silica was used as the sorbent in solid-phase extraction to determine theophylline in blood serum with satisfactory recovery higher than 90%. Nonspecific adsorption of interfering compounds can be eliminated by a simple elution with acetonitrile, without sacrificing the selective binding of theophylline.     

Synthesis of polystyrene-styrene/butadiene diblock copolymers via reversible addition-fragmentation chain transfer miniemulsion polymerization

<正>Polystyrene-styrene/butadiene diblock copolymers were synthesized via reversible addition-fragmentation chain transfer (RAFT) miniemulsion polymerization.During the polymerization process,the molecular weight distribution was narrow and the numerical molecular weight of the copolymers increased with increasing conversion of monomers,which was close to the theoretical.FT-IR and ~1H NMR results indicated that the microstructure of the polymer was mainly 1,4-trans-butadiene with small amount of 1,2-units,and composition in the copolymers was obtained.     

Monolithic poly(ethylhexyl methacrylate-co-ethylene dimethacrylate) column with restricted access layers prepared via reversible addition-fragmentation chain transfer polymerization

The "living"/controlled radical polymerization has provided an opportunity in making a more homogeneous polymer, which is favorable for polymer-based monolithic column fabrication. To study its application in the preparation of separation material, a capillary poly(ethylhexyl methacrylate-co-ethylene dimethacrylate) monolithic column has been synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. The correlation between the synthetic conditions and the polymer structures and separation performance was studied. The result indicated RAFT-mediated reaction provides condition for creating polymers with narrower pore size distribution and higher column efficiency compared with traditional polymerization. The "living" property of the RAFT polymerization was further utilized to graft hydrophilic polymer on the surface of poly(ethylhexyl methacrylate-co-ethylene dimethacrylate). The hydrophilic chain modified monolithic column has both abilities of protein exclusion and small hydrophobic compound retention. The result indicated that RAFT polymerization can be used for making multifunctional material. The restricted access monolithic material synthesized by this method can be used in biological sample analysis with HPLC direct injection.     

The reversible addition-fragmentation chain transfer （RAFT） miniemulsion polymerization of vinyl acetate mediated by xanthate

The reversible addition-fragmentation chain transfer(RAFT) miniemulsion polymerization of vinyl acetate(VAc) mediated by methyl(methoxycarbonothioyl) sulfanyl acetate(MMSA) was carried out.The results showed that polymerizations initiated by AIBN and KPS proceeded in a controlled way.The RAFT miniemulsion polymerization of VAc initiated by KPS showed the shorter inhibition period,higher propagation rate coefficient and final conversion than those in experiment initiated by AIBN.When the monomer conversio...     

Synthesis and characterization of graft copolymers based on polyepichlorohydrin via reversible addition-fragmentation chain transfer polymerization

In this study, synthesis of poly(epichlorohydrin-g-methyl methacrylate) graft copolymers by reversible addition-fragmentation chain transfer (RAFT) polymerization was reported. For this purpose, epichlorohydrin was polymerized by using HNO₃ via cationic ring-opening mechanism. A RAFT macroinitiator (macro-RAFT agent) was obtained by the reaction of potassium ethyl xanthogenate and polyepichlorohydrin. The graft copolymers were synthesized using macro-RAFT agent as initiator and methyl methacrylate as monomer. The synthesis of graft copolymers was conducted by changing the time of polymerization and the amount of monomer-initiator concentration that affect the RAFT polymerization. The effects of these parameters on polymerization were evaluated via various analyses. The characterization of the products was determined using ¹H-nuclear magnetic resonance (¹H-NMR), Fourier-transform infrared spectroscopy, gel-permeation chromatography, thermogravimetric analysis, elemental analysis, and fractional precipitation techniques. The block lengths of the graft copolymers were calculated by using ¹H-NMR spectrum. It was observed that the block length could be altered by varying the monomer and initiator concentrations.     

Preparation of imprinted monolithic column under molecular crowding conditions

Molecular crowding is a new concept to obtain molecularly imprinted polymers(MIPs) with greater capacity and selectivity.In this work,molecular crowding agent was firstly applied to the preparation of MIPs monolithic column.A new polymerization system based on molecular crowding surrounding was developed to prepare enrofloxacin-imprinted monolith,which was composed of polystyrene and tetrahydrofuran.The result showed that the monolithic MIPs under molecular crowding conditions presented good molecular recognition for enrofloxacin with an imprinting factor of 3.03.     

Chiral separation by （S）-naproxen imprinted monolithic column with mixed functional monomers

Molecularly imprinted polymers (MIPs), using (S)-naproxen as template and the combination of butyl methacrylate (BMA) and MAA (1:1 molar ratio) as functional monomers were synthesized by an in situ polymerization reaction. The rendered monolithic column was evaluated in HPLC mode. The result showed that the monolithic MIPs with the combination of two monomers produced better chiral resolution of rac-naproxen (Rs=1.55) and column efficiencies of imprinted molecules (N=2860 plates/m)than that with pure MAA.     

Low cross-linked molecularly imprinted monolithic column prepared in molecular crowding conditions

Molecular crowding is a new approach to promoting molecular imprinting more efficiently. In this work, this concept was applied to the preparation of low cross-linked imprinted polymers in the presence of an immobilised template for stabilizing binding sites and improving molecular recognition. An imprinted monolithic column was synthesized using a mixture of 2,4-diamino-6-methyl-1,3,5-triazine (template), 2,4-diamino-6-(methacryloyloxy) ethyl-1,3,5-triazine (polymerisable template), methacrylic acid, ethylene glycol dimethacrylate, and polystyrene (molecular crowding agent). Some polymerization factors, such as template-monomer molar ratio, the composition of the porogen and crosslinking density, on the imprinting effect of resulting MIP monolith were systematically investigated. The results indicated that the imprinted monolithic columns prepared in the presence of molecular crowding agent retained affinity and specificity for template even when prepared with a level of cross-linker as low as 9%. Moreover, a stoichiometric displacement model for retention was successfully applied to evaluate the interaction between the solute and the stationary phase. Compared with the low cross-linked MIP prepared by conventional polymerization, the molecular crowding-based low cross-linked monolithic MIPs showed higher selectivity. The results suggested that molecular crowding is a powerful strategy to increase the effect of molecular imprinting at a low level of crosslinker.     

Grafting polymer nanoshell onto the exterior surface of mesoporous silica nanoparticles via surface reversible addition-fragmentation chain transfer polymerization

Reversible addition-fragmentation chain transfer (RAFT) functionalities were anchored to the exterior surface of mesoporous silica nanoparticles (MSNs) without changing the mesoporous structure, RAFT polymerization of styrene was subsequently conducted to graft polystyrene (PSt) onto the exterior surface of MSNs, forming a novel core-shell nanostructure with a mesoporous core and a polymer nanoshell. Fourier transform infrared spectroscopy (FT-IR), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) were used to characterize the produced mesoporous core-shell nanostructure, the results showed that the thickness of the nanoshell increased with the increasing time of polymerization.     

Synthesis and characterizations of 1,2,3-triazole containing polymers via reversible addition-fragmentation chain transfer (RAFT) polymerization

A novel monomer containing triazole and naphthalene ring, 2-(1-naphthalen-1-ylmethyl-1H-[1,2,3]triazol-4-yl)-ethyl methacrylate (NTEMA), was designed and synthesized via “click” chemistry method. The RAFT polymerization of NTEMA was successfully carried out using 2-cyanoprop-2-yl dithiobenzoate (CPDB) as a RAFT agent, 2,2′-azobisisobutyronitrile (AIBN) as an initiator in tetrahydrofuran (THF) solution. The results showed that the polymerizations exhibited “living”/controlled characteristics. The obtained poly(2-(1-naphthalen-1-ylmethyl-1H-[1,2,3]triazol-4-yl)-ethyl methacrylate) homopolymers, PNTEMAs, were further coordinated with samarium ion to prepare rare earth containing polymers (PNTEMA-Sm(III) complexes) which were characterized by FT-IR, DSC and ICP-AES. The characterization data confirmed that triazole in side chain of the polymer could coordinate with Sm(III). The fluorescence property of the polymers and polymer Sm(III) complexes were investigated in solution and in film.     

Synthesis of amphiphilic block copolymers via ring opening polymerization and reversible addition-fragmentation chain transfer polymerization

Amphiphilic block copolymers were synthesized via a dual initiator chain transfer agent (inifer) that successfully initiated the ring opening polymerization (ROP) of l -lactide (LLA) and subsequently mediated the reversible addition-fragmentation chain transfer (RAFT) polymerization of poly(ethylene glycol) ethyl ether methacrylate (PEGEEMA). The formation of each polymer block was confirmed using ¹H nuclear magnetic resonance spectroscopy, as well as gel permeation chromatography, and comprehensive kinetics studies provide valuable insights into the factors influencing the synthesis of well-defined block copolymers. The effect of monomer concentration, reaction time, and molar ratios of inifer to catalyst on the ROP of LLA are discussed, as well as the ability to produce poly(lactide) blocks of different molecular weights. The synthesis of hydrophilic PPEGEEMA blocks was also monitored via kinetics to provide a better understanding of the role the chain transfer agent plays in facilitating the complex and sterically demanding RAFT polymerization of PEGEEMA.     

Preparation and characterization of a molecularly imprinted monolithic column for pressure‐assisted CEC separation of nitroimidazole drugs

A polymethacrylate‐based molecularly imprinted monolithic column bearing mixed functional monomers, using non‐covalent imprinting approach, was designed for the rapid separation of nitroimidazole compounds. The new monolithic column has been prepared via simple in situ polymerization of 2‐hydroxyethyl methacrylate, dimethylaminoethyl methacrylate and ethylene dimethacrylate, using (S)‐ornidazole ((S)‐ONZ) as template in a binary porogenic mixture consisting of toluene and dodecanol. The composition of the polymerization mixture was systematically altered and optimized by altering the amount of monomers as well as the composition of the porogenic solvent. The column performance was evaluated in pressure‐assisted CEC mode. Separation conditions such as pH, voltage, amount of organic modifier and salt concentration were studied. The optimized monolithic column resulted in excellent separation of a group of structurally related nitroimidazole drugs within 10 min in isocratic elution condition. Column efficiencies of 99 000, 80 000, 103 000, 60 000 and 99 000 plates/m were obtained for metronidazole, secnidazole, ronidazole, tinidazole and dimetridazole, respectively. Parallel experiments were carried out using molecularly imprinted and non‐imprinted capillary columns. The separation might be the result of combined effects including hydrophobic, hydrogen bonding and the imprinting cavities on the (S)‐ONZ‐imprinted monolithic column.     

Selective recognition of Triamterene in biological samples by molecularly imprinted monolithic column with a pseudo template employed

Melamine (MAM) was employed as a pseudo template to prepare a molecularly imprinted polymer monolithic column which presents the ability of selective recognition to Triamterene (TAT), whose structure was similar to that of MAM. Methacrylic acid and ethylene glycol dimethacrylate were applied as functional monomer and cross‐linker, respectively, during the in situ polymerization process. Chromatographic behaviors were evaluated, the results indicated that the molecularly imprinted polymer monolithic column possessed excellent affinity and selectivity for TAT, and the imprinting factor was high up to 3.99 when 7:3 of ACN/water v/v was used as mobile phase. In addition, the dissociation constant and the binding sites were also determined by frontal chromatography as 134.31 μmol/L and 132.28 μmol/g, respectively, which demonstrated that the obtained molecularly imprinted polymer monolith had a high binding capacity and strong affinity ability to TAT. Furthermore, biological samples could be directly injected into the column and TAT was enriched with the optimized mobile phase. These assays gave recovery values higher than 91.60% with RSD values that were always less than 3.5%. The molecularly imprinted monolithic column greatly simplified experiment procedure and can be applied to preconcentration, purification, and analysis of TAT in biological samples.     

可逆加成-断裂链转移自由基聚合研究进展

综述了活性/可控自由基聚合中的可逆加成-断裂链转移(RAFT)自由基聚合研究进展;总结了RAFT试剂、RAFT聚合反应条件、RAFT聚合物及其结构形貌的最新研究进展;指出RAFT自由基聚合反应已被作为重要方法之一用于合成具有特定分子结构的聚合物.     

Synthesis of Poly(styrene sulfonyl chloride) via reversible addition-fragmentation chain transfer polymerization and characterization thereof for membrane applications

Reversible addition-fragmentation chain transfer (RAFT) polymerization has been examined for the synthesis of poly (styrene sulfonyl chloride) (PSSC) of high molecular weight and narrow polydispersity index (PDI). PSSC, contains reactive sulfonyl chloride that can allow use of organic solvent for membrane casting, and chemical modification through reactive sulfonyl groups. For PSSC preparation, end-capped styrene i.e. styrene sulfonyl chloride (SSC) is used as a monomer, which is derived from sodium 4-vinylbenzenesulfonate by chlorination with thionyl chloride. Fourier transform infrared spectroscopy, Raman spectroscopy and Proton nuclear magnetic resonance spectroscopy, have been successfully used to confirm the polymer architecture. End-group of PSSC containing RAFT agent (Cyanomethyl N-methyl-N-phenylcarbamodithioate), is also confirmed by fragmentation analysis using Gas chromatography-mass spectroscopy. Evaluation of PSSC by X-ray diffraction and differential scanning calorimetry showed that resulting polymer is predominantly amorphous in nature and has a glass transition temperature of 119 ​°C. Gel permeation chromatography data reveals formation of high molecular weight (84 ​kDa) PSSC with and low PDI (1.4). Moreover, PSSC can be converted to polyelectrolyte and can be crosslinked by interfacial polymerization concept; hence, it would have considerable prospective for membrane preparation for fuel cell and water purification.     

Molecularly imprinted polymer coated solid-phase microextraction fiber prepared by surface reversible addition–fragmentation chain transfer polymerization for monitoring of Sudan dyes in chilli tomato sauce and chilli pepper samples

Surface reversible addition-fragmentation chain transfer (RAFT) polymerization method was firstly applied to the preparation of molecularly imprinted polymer (MIP) coated silicon solid-phase microextraction (SPME) fibers. With Sudan I as template, an ultra-thin MIP coating with about 0.55-μm thickness was obtained with homogeneous structure and controlled composition, due to the controllable radical growing and chain propagation in surface RAFT polymerization. The MIP-coated fibers were found with enhanced selectivity coefficients (3.0–6.5) to Sudan I–IV dyes in contrast with those reported in our previous work. Furthermore, the ultra-thin thickness of MIP coating was helpful to the effective elution of template and fast adsorption/desorption kinetics, so only about 18 min was needed for MIP-coated SPME operation. The detection limits of 21–55 ng L⁻¹ were achieved for four Sudan dyes, when MIP-coated SPME was coupled with liquid chromatography (LC) and mass spectrometry (MS) detection. The MIP-coated SPME–LC–MS/MS method was tested for the monitoring of ultra trace Sudan dyes in spiked chilli tomato sauce and chilli pepper samples, and high enrichment effect, remarkable matrix peaks-removing capability, and consequent high sensitivities were achieved to four Sudan dyes.     

Novel preparation of monolithic imprinted columns for electrochromatographic separation by photopolymerization

A monolithic molecularly imprinted polymer with specific recognition ability for 4-hydroxybenzoic acid (4-HBA) was prepared by in situ photopolymerization, using methacrylic acid (MAA) as a functional monomer, ethylene glycol dimethacrylate (EDMA) as a cross-linking agent, toluene and isooctane as porogenic solvents and Irgacure 1800 as an initiator. Baseline separation of isomers of hydroxybenzoic acid was achieved in less than 8 min on this monolithic column using 4-HBA as template, but not on the blank polymer. Furthermore, some neutral compounds could also be baseline-separated on the imprinted polymer column in the mode of pressure-driven capillary electrochromatography.     

Synthesis of tetracycline‐imprinted polymer microspheres by reversible addition–fragmentation chain‐transfer precipitation polymerization using polyethylene glycol as a coporogen

Tetracycline (TC)‐imprinted microspheres have been synthesized by reversible addition–fragmentation chain‐transfer precipitation polymerization using PEG as a coporogen. In the synthesis, methacrylic acid and ethylene dimethacrylate were used as the functional monomer and cross‐linker, respectively. 2,2′‐Azobisisobutyronitrile was the initiator, and cumyl dithiobenzoate was the chain‐transfer reagent. Although monodispersed microspheres were obtained using acetonitrile as porogen, the particles cannot be used in the column extraction because of the high backpressure. To increase the porosity of the material, PEG was introduced as a coporogen. The influence of the molecular weight and concentration of PEG on the morphology, binding affinity, and porosity of the molecularly imprinted polymers (MIPs) have been studied. The results demonstrated that PEG as a macroporogen increased the porosity of the polymers. Meanwhile, the column backpressure was reduced using the MIPs with higher porosity. The binding affinity of the MIPs was increased when a low concentration of PEG was employed, while it was decreased when the ratio of PEG 12 000/monomers was >0.8%. Under the optimized conditions, TC‐imprinted microspheres with good selectivity and size uniformity have been obtained, which facilitates its application in the column extraction for TC determinations.