Reversible Addition-fragmentation Chain Transfer Precipitation Research Articles

Synthesis of heat-resistant living polymer particles by one-step reversible addition-fragmentation chain transfer precipitation polymerization of styrene and N-phenylmaleimide

For the first time, the synthesis of heat-resistant, “living” polymer particles via one-step reversible addition-fragmentation chain transfer precipitation polymerization (RAFTPP) of styrene (St) and N-phenylmaleimide (PhMI) is reported. Gel permeation chromatography and nuclear magnetic resonance spectroscopy confirmed that the polymerization proceeded in a living manner. The scanning electron microscopy results showed that the monodisperse P(St-PhMI)_RAFTPP particles with a diameter of 1.88 μm were successfully synthesized. The P(St-PhMI)_RAFTPP showed excellent thermal stability with a high glass transition temperature and a 5% weight loss temperature. The surface concentration of the RAFT groups was determined to be 0.181 groups/nm2 due to fragmentation of the RAFT groups exposed on the particles. The small-angle neutron scattering measurements showed the particle formation mechanism, in which the swollen, growing polymer chains were consumed for particle formation. The introduction of grafted chains by surface-initiated RAFT polymerization demonstrated the possibility of further functionalization of P(St-PhMI)_RAFTPP particles by exploiting their living nature.

Aqueous solution behavior of thermoresponsive polyzwitterionic microgels based on poly(N-vinylcaprolactam) synthesized via RAFT precipitation polymerization

A new route to synthesize stimuli-responsive poly(N-vinylcaprolactam) (PNVCL) microgels decorated with zwitterionic poly(sulfobetaine) (PSB) chains was developed, using reversible addition–fragmentation chain transfer (RAFT) precipitation polymerization. The polyzwitterionic PSB macro-RAFTs of controlled molecular weight were synthesized by RAFT polymerization of sulfobetaine (SB). Using this method, macro-RAFTs with good control over the molecular weight could be achieved. The PSB macro-RAFTs, having different molecular weights (1000, 5000, 10,000 g/mol) and concentrations (1, 2, 2.5 mol%), were used along with different amount of the cross-linker N,N'-methylenebisacrylamide (BIS) (1.5 and 2.5 mol%) in the precipitation polymerization of PNVCL microgels to obtain varying amounts of surface-grafted polyzwitterionic chains of controlled length and variable cross-linking degrees. The successful incorporation of PSB macro-RAFTs into PNVCL microgels was characterized by FTIR and 1H NMR studies. Increasing the PSB concentration and BIS content in the PNVCL microgels resulted in a linear increase in electrophoretic mobility (µe) and volume phase transition temperature (VPTT). However, increasing the molecular chain length of the zwitterionic macro-RAFT resulted in a shift of VPTT towards lower temperatures. This kind of stimuli-responsive, polyzwitterion decorated PNVCL microgels can be a potential material for biomedical applications.

Narrow or Monodisperse, Physically Cross-Linked, and “Living” Spherical Polymer Particles by One-Stage RAFT Precipitation Polymerization

Controlled preparation of narrow or monodisperse, physically cross-linked, and “living” spherical polymer particles by one-stage reversible addition–fragmentation chain transfer (RAFT) precipitation polymerization (RAFTPP) is described for the first time. The introduction of RAFT polymerization mechanism into precipitation polymerization system, together with the use of methacrylic acid (MAA) (capable of forming hydrogen bonding) as the monomer, allows ready generation of uniform spherical poly(MAA) (PMAA) particles with surface-bound “living” dithioester groups, easily tunable sizes, and low molecular weights in the absence of any cross-linking monomer. The polymerization parameters (i.e., monomer loading, molar ratio of the RAFT agent to free radical initiator, and polymerization temperature) showed much influence on the morphologies and yields of PMAA particles, and their simple adjustment allows fine-tuning of “living” PMAA particle sizes. The presence of dithioester groups on such PMAA particles was ...

Capturing Cadmium(II) Ion from Wastewater Containing Solid Particles and Floccules Using Ion-Imprinted Polymers with Broom Effect

Cavities and adsorption sites in adsorption materials can be easily blocked in complex media containing solid particles and floccules, which limit the applicability of these materials. This study demonstrates the synthesis of cadmium(II) ion-imprinted polymers (Cd-IIPs) and nonion-imprinted polymers (NIPs) via reversible addition–fragmentation chain transfer precipitation polymerization (RAFTPP). Microspheres of IIPs and NIPs were modified by grafting bicomponent polymer brushes with different ratios of a hydrophilic component, hydroxyethyl methacrylate (HEMA), and a rigid component, styrene. The maximum adsorption capacities of the IIPs and NIPs in pure water are 65.5 and 24.5 mg/g, respectively. Specifically, the 9:1-IIP exhibits excellent antiblockage and anti-interference performance, with an adsorption capacity considerably higher than those of IIPs in simulated wastewater including SiO2 solid particles and floccules. This higher performance suggests that the 9:1-IIP has the rigidity to resist chaff ...

Preparation of hydrophilic surface-imprinted ionic liquid polymer on multi-walled carbon nanotubes for the sensitive electrochemical determination of imidacloprid

A hydrophilic ionic liquid monomer was immobilized on carboxylated MWNTs by ion exchange, then reversible addition–fragmentation chain transfer precipitation polymerization was performed in the presence of a template, imidacloprid.

Water-compatible temperature and magnetic dual-responsive molecularly imprinted polymers for recognition and extraction of bisphenol A

Versatile molecularly imprinted polymers (MIPs) have been widely applied to various sample matrices, however, molecular recognition in aqueous media is still difficult. Stimuli-responsive MIPs have received increasing attentions due to their unique feature that the molecular recognition is regulated by specific external stimuli. Herein, water-compatible temperature and magnetic dual-responsive MIPs (WC-TMMIPs) with hydrophilic brushes were prepared via reversible addition-fragmentation chain transfer precipitation polymerization for reversible and selective recognition and extraction of bisphenol A (BPA). Transmission electron microscopy (TEM), Fourier transform infrared spectrometer (FT-IR) and vibrating sample magnetometry (VSM) as characterization methods were used to examine the successful synthesis of polymers, and the resultant WC-TMMIPs showed excellent thermosensitivity and simple rapid magnetic separation. Controlled adsorption and release of BPA by temperature regulation were investigated systematically, and the maximum adsorption and removal efficiency toward BPA in aqueous solutions were attained at 35°C and 45°C, respectively, as well as a good recoverability was exhibited with the precision less than 5% through five adsorption–desorption cycles. Phenolic structural analogs were tested and good recognition specificity for BPA was displayed. Accordingly, the WC-TMMIPs were employed as adsorbents for magnetic solid-phase extraction (MSPE) and packed SPE of BPA from seawater samples. Using the two modes followed by HPLC-UV determination, excellent linearity was attained in the range of 0.1–14.5μM and 1.3–125nM, with low detection limits of 0.02μM and 0.18nM, respectively. Satisfactory recoveries for spiked seawater samples were achieved ranging from 86.3–103.5% and 96.2–104.3% with RSD within 2.12–4.33%. The intelligent WC-TMMIPs combining water-compatibility, molecular recognition, magnetic separation, and temperature regulation proved potentially applicable for selective identification, controlled adsorption/release and high-efficiency enrichment/removal of trace targets in complicated aqueous media.

Synthesis of water-compatible surface-imprinted polymer via click chemistry and RAFT precipitation polymerization for highly selective and sensitive electrochemical assay of fenitrothion

A novel water-compatible fenitrothion imprinted polymer was prepared on Au nanoparticles (AuNPs) by click chemistry and reversible addition–fragmentation chain transfer (RAFT) precipitation polymerization (RAFTPP). The RAFT chain-transfer agent was synthesized on the surface of AuNPs using click chemistry, then an imprinted polymer with hydrophilic polymer brushes was prepared on the RAFT chain-transfer agent modified AuNPs by RAFTPP, mediated by hydrophilic polyethylene glycol macromolecular cochain-transfer agent. The obtained molecularly imprinted material showed improved accessibility to fenitrothion and recognition property in water medium. When the material was immobilized on an ionic liquid functionalized graphene coated glassy carbon electrode for the electrochemical determination of fenitrothion, the resulting electrochemical sensor presented linear response in the range of 0.01−5μM, with a sensitivity of 6.1μA/μMmm2. The low limit of detection was 8nM (S/N=3). The sensor was successfully applied to the determination of real samples and the recovery for standard added was 95−108%.

Preparation of surface-imprinted polymer grafted with water-compatible external layer via RAFT precipitation polymerization for highly selective and sensitive electrochemical determination of brucine

A novel brucine imprinted polymer was prepared on multi-walled carbon nanotubes by reversible addition–fragmentation chain transfer (RAFT) precipitation polymerization. The polymer was further grafted with hydrophilic poly(glycerol monomethacrylate) brushes to improve its water-compatibility. The obtained molecularly imprinted material showed enhanced accessibility to brucine and improved selective recognition property in water medium. When the material was supported on an ionic liquid functionalized graphene coated glassy carbon electrode for the electrochemical determination of brucine, the resulting electrochemical sensor presented good analytical performance. Under the optimized conditions, the peak current was linear to brucine concentration in the ranges of 0.006−0.6μM and 0.6−5.0μM with sensitivities of 15.3μA/μMmm2 and 5.4μA/μM mm2, respectively; the detection limit was 2nM (S/N=3). The sensor was successfully applied to the determination of brucine in practical samples and the recovery for the standards added was 94−104%.

Preparation and evaluation of vanillin molecularly imprinted polymer microspheres by reversible addition–fragmentation chain transfer precipitation polymerization

Novel vanillin molecularly imprinted polymer microspheres were synthesized by the method of the reversible addition–fragmentation chain transfer (RAFT) precipitation polymerization. In the study, the imprinted polymer was synthesized by using dibenzyltrithiocarbonate (DBTTC) and vanillin as the chain transfer agent and template respectively. Ultraviolet spectrum analysis was used to determine methacrylic acid (MAA) as the functional monomer. The conditions which influence the preparation of the molecularly imprinted polymer prepared by RAFT (RAFT-MIP) such as solvent, crosslinker, and the ratio of monomer, AIBN and DBTTC were systematically investigated. Scanning election microscopy, adsorption experiment and Scatchard analysis were used to evaluate the RAFT-MIP. The morphology and adsorption performance of RAFT-MIP were improved significantly in comparison with molecularly imprinted polymers synthesized by traditional precipitation polymerization (TR-MIP).

Water-compatible poly (hydroxyethyl methacrylate) polymer sorbent for miniaturized syringe assisted extraction of sulfonamides in milk

A simple, convenient, and economic self-assembly miniaturized syringe assisted extraction (mini-SAE) using poly (hydroxyethyl methacrylate) polymer (PHEMA) as sorbent coupled with liquid chromatography was proposed for rapid screening of sulfadiazine (SD) and sulfamonomethoxine (SMM) in milk. The water-compatible PHEMA was synthesized by reversible addition-fragmentation chain transfer precipitation polymerization using trithiocarbonate as chain transfer agent and methanol–water system as reaction medium. The obtained PHEMA sorbent showed good affinity to sulfonamides and was successfully applied as a special sorbent for a mini-SAE device for simultaneous extraction and isolation of SD and SMM in milk samples. Under the optimum condition, good linearity was obtained in a range of 7.0–700ngg−1 (r≥0.9995) and the average recoveries of SD and SMM at three spiked levels were ranged from 85.6 to 100.3% with the relative standard deviations (RSD) ≤6.5%. The presented PHEMA-mini-SAE protocol could be potentially applied as an alternative tool for analyzing the residues of SAs in complicated biological samples.

Preparation of a Pyrazosulfuron-Ethyl Imprinted Polymer with Hydrophilic External Layers by Reversible Addition-Fragmentation Chain Transfer Precipitation and Grafting Polymerization

A new imprinted polymer with both functions of molecular recognition and macromolecule exclusion was synthesized for selective extraction of pyrazosulfuron-ethyl and removal of humic acids in environmental analysis. In the preparation, spherical pyrazosulfuron-ethyl imprinted polymers were synthesized by reversible addition–fragmentation chain transfer (RAFT) precipitation polymerization. The hydrophilic polymer layers were then grafted on the surface of the imprinted polymer microspheres using post-RAFT polymerization. The conditions that influence the selectivity, size, and uniformity of the imprinted microspheres were studied systematically. The computer simulation was employed to study the template-monomer interaction. The solubility parameters of poly(MAA-co-EDMA) and porogen were calculated to investigate the relationship between the particle size and the solubility parameter. The results indicated that the pyrazosulfuron-ethyl imprinted polymers have special affinity for the template and several structurally related sulfonylurea herbicides. The molecularly imprinted polymer (MIP) with external hydrophilic chains not only had function of template retention, but also better function of protein/humic acid exclusion. This research demonstrates that multifunctional imprinted material with a narrow size distribution can be prepared by the RAFT polymerization.

Efficient One‐Pot Synthesis of Water‐Compatible Molecularly Imprinted Polymer Microspheres by Facile RAFT Precipitation Polymerization

Molecular imprinting is a versatile and straightforward method for the preparation of polymer receptors with tailor-made recognition sites. Despite the tremendous progress made in this field, many challenges still remain to be addressed. In particular, it has been shown that the presently developed molecularly imprinted polymers (MIPs) are normally only organic solvent compatible and they mostly fail to show specific template bindings in pure aqueous solutions, thus significantly limiting their practical applications in the field of biotechnology. Although some approaches, which either use specifically designed functional monomers or apply the conventional imprinting protocol, have been developed for the preparation of MIPs with molecular recognition ability under aqueous conditions, versatile approaches for the preparation of MIPs that are applicable in pure aqueous environments are still rare. Herein, we report a new and efficient one-pot approach to obtain pure-water-compatible and narrowly dispersed MIP microspheres with surface-grafted hydrophilic polymer brushes by facile reversible addition/fragmentation chaintransfer (RAFT) precipitation polymerization (RAFTPP), mediated by hydrophilic macromolecular chain-transfer agents (Macro-CTAs; Scheme 1). The presence of hydrophilic polymer brushes on MIP microspheres significantly improved their surface hydrophilicity and dramatically reduced their hydrophobic interactions with template molecules in pure aqueous media, thus leading to their water compatibility. The easy availability of many different hydrophilic Macro-CTAs (by either RAFT polymerization of hydrophilic monomers or hydrophilic polymer end group modification), together with the versatility of RAFTPP for the controlled preparation of MIP microspheres, makes this strategy highly applicable for the design of hydrophilic and water-compatible MIPs. Two strategies have been developed for the synthesis of water-compatibleMIPs by improving their surface hydrophilicity; these strategies involve the use of a hydrophilic comonomer, functional monomer, or crosslinker in the molecular imprinting process, and the postmodification of the preformed MIPs. Although simple in principle, the former strategy either requires time-consuming optimization of MIP formulation components or can only be applied in some special systems. In comparison, the latter strategy, which involves the surface grafting of hydrophilic polymer layers, has proven highly attractive because it not only significantly improves the MIPs surface hydrophilicity, but also provides a protective layer to prevent protein molecules from blocking their imprinting sites in biological solutions. Very recently, we have successfully prepared pure-water-compatible MIP microspheres by the controlled grafting of hydrophilic polymer layers onto the preformed MIP particles. Compared with this two-step approach, the new strategy presented herein allows the more efficient controlled synthesis of pure-water-compatible MIP microspheres with surface-grafted hydrophilic polymer brushes by a one-pot RAFTPP method. To show proof-of-principle for our strategy, a model noncovalent molecular imprinting system was chosen because Scheme 1. Chemical structures of the utilized RAFT agents (including hydrophilic Macro-CTAs and CDB) and the schematic protocol for the one-pot preparation of water-compatible MIP microspheres by RAFT precipitation polymerization.

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 2.89mgg−1 and 1.53mgg−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.

Preparation of molecularly imprinted polymer microspheres via reversible addition–fragmentation chain transfer precipitation polymerization

The first combined use of reversible addition–fragmentation chain transfer (RAFT) polymerization and precipitation polymerization in the molecular imprinting field is described. The new polymerization technique, namely RAFT precipitation polymerization (RAFTPP), provides MIP microspheres with obvious molecular imprinting effects towards the template, fast template binding process and an appreciable selectivity over structurally related compounds, while only irregular MIP aggregates were obtained via traditional radical precipitation polymerization (TRPP) under similar reaction conditions. The MIP microspheres prepared via RAFTPP have proven to show improved binding capacity, larger binding constant and apparent maximum number for high-affinity sites, and significantly higher high-affinity binding site density in comparison with the MIP prepared via TRPP.