Anhou Xu

Highly porous and chemical resistive P(TFEMA–DVB) monolith with tunable morphology for rapid oil/water separation

A facile preparation for a series of porous poly(2,2,2-trifluoroethylmethacrylate–divinylbenzene) P(TFEMA–DVB) foams is discussed in this paper. The foams have adjustable morphology utilizing a suitable commercial surfactant, Hypermer B246, as stabilizer, and were compared with traditional organic surfactants or macromolecular block-polymers. Combining the porous properties and advantages of fluorine atoms, this type of fluoropolymer exhibited superb chemical stability and hydrophobicity performances with high porosity. These porous fluoro-monoliths preserved their regular porous structure without any degradation after immersion into strong acidic or basic solution for three days, hence demonstrating an excellent potential to deal with environmental pollution caused by oil spillages in severe environments. The tunable morphology (open and closed pores) and pore sizes were achieved by investigating various parameters like surfactant concentration, amount of external crosslinker, and aqueous phase volume. Droplet sizes of HIPEs were characterized using an optical microscope under different experimental conditions. The influence of pore structure and surface properties of polyHIPE on water contact angle and oil adsorption capacity was also explored. The results indicated that the porous material has an excellent oleophilicity and hydrophobicity, with water contact angles (WCA) up to 146.4°. Additionally, the results presented a noticeable adsorption with a very fast rate towards organic oils from either a water surface or bottom with adsorption saturation achieved in about 120 s. The prepared polyHIPEs showed a good recycling ability; even after 10 adsorption–centrifugation experiments, the adsorption capacity was still more than 85%.

Synthesis of fluorinated nanoparticles via RAFT dispersion polymerization-induced self-assembly using fluorinated macro-RAFT agents in supercritical carbon dioxide

A series of poly(dodecafluoroheptyl methacrylate)-b-poly(methyl methacrylate) (PDFMA-b-PMMA) diblock copolymer nanoparticles were prepared by reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization of methyl methacrylate (MMA) in supercritical carbon dioxide. Nuclear Magnetic Resonance (NMR) and gel permeation chromatography (GPC) analysis confirmed an efficient and well-controlled block copolymerization. As the length of the PMMA block grows from the soluble PDFMA block it eventually becomes insoluble, which drives in situ polymerization-induced self-assembly (PISA). The influences of the length of CO2-philic PDFMA block, CO2-phobic PMMA block and polymerization pressure were investigated in this PISA process. Also spherical nano-objects were formed upon the synthesis of amphiphilic diblock copolymers in situ. It appeared that, as the length of CO2-philic block PDFMA was increased, there was a corresponding decrease in particle size and particle size polydispersity. Scanning electron microscope (SEM) images revealed that, during the microspheres formation, the greater degree of polymerization (DP) of MMA favoured well-controlled monodisperse microspheres.

Preparation of Thermo-Responsive and Cross-Linked Fluorinated Nanoparticles via RAFT-Mediated Aqueous Polymerization in Nanoreactors

In this work, a thermo-responsive and cross-linked fluoropolymer poly(2,2,2-Trifluoroethyl) methacrylate (PTFEMA) was successfully prepared by reversible addition-fragmentation chain transfer (RAFT) mediated aqueous polymerization with a thermo-responsive diblock poly(dimethylacrylamide-b-N-isopropylacrylamide) (PDMA-b-PNIPAM) that performed a dual function as both a nanoreactor and macro-RAFT agent. The cross-linked polymer particles proved to be in a spherical-like structure of about 50 nm in diameter and with a relatively narrow particle size distribution. 1H-NMR and 19F-NMR spectra showed that thermo-responsive diblock P(DMA-b-NIPAM) and cross-linked PTFEMA particles were successfully synthesized. Influence of the amount of ammonium persulfate (APS), the molar ratio of monomers to RAFT agent, influence of the amount of cross-linker on aqueous polymerization and thermo-responsive characterization of the particles are investigated. Monomer conversion increased from 44% to 94% with increasing the molar ratio of APS and P(DMA-b-NIPAM) from 1:9 to1:3. As the reaction proceeded, the particle size increased from 29 to 49 nm due to the consumption of TFEMA monomer. The size of cross-linked nanoparticles sharply decreased from 50.3 to 40.5 nm over the temperature range 14–44 °C, suggesting good temperature sensitivity for these nanoparticles.

An alternating copolymer of maleic anhydride and ethyl vinyl ether: synthesis in supercritical carbon dioxide, characterization, and properties

Alternative copolymers of maleic anhydride (MA) and ethyl vinyl ether (EVE) [P(MA-alt-EVE)] were prepared in supercritical carbon dioxide (scCO2). The chemical structure of the obtained P(MA-alt-EVE)s was characterized by FT-IR and 13C NMR spectroscopy and showed that the copolymers possess strictly alternating structure. The influences of MA/EVE feed ratio, reaction time, and solvent as well as the initial initiator concentration on the copolymerization were also studied. It was indicated that the increase rate of reaction pressure could be related with good accuracy to monomer conversion, providing a simple and efficient method for monitoring the reaction processes. Gel Permeation Chromatography examination of the alternative copolymers revealed that the molecular weights of P(MA-alt-EVE) synthesized in scCO2 at different pressures were all higher than those prepared in organic solvents. Thermal properties were investigated by TGA and showed P(MA-alt-EVE) has good thermal stability (T d = 251 °C). Comparison studies on the P(MA-alt-EVE) in scCO2 and that prepared in organic solvent exhibit scCO2 solvent and it plays an important role in the copolymerization of MA and EVE.

Methyl Methacrylate HIPE Solely Stabilized by Fluorinated Di‐block Copolymer for Fabrication of Highly Porous and Interconnected Polymer Monoliths

Preparation of stable water-in-oil (W/O) high internal phase emulsion (HIPE) containing methyl methacrylate (MMA) monomer as oil phase is a difficult task due to the significant solubility of MMA in water. Here, for the first time a fluorinated di-block copolymer (FDBC) poly (2-dimethylamino)ethylmethacrylate-b-poly (trifluoroethyl methacrylate) (PDMAEMA-b-PTFEMA) is proposed to stabilize HIPEs of MMA without the use of any co-stabilizer or thickening agent. Fluorinated segments in FDBC anchored well at oil/water interface of HIPE, offering high hydrophobicity to the partially hydrophilic MMA monomer and in turn stabilization to MMA-HIPE. By using fluorinated di-block copolymer as stabilizer, highly stable HIPEs can be obtained. In addition, highly interconnected porous monoliths were obtained after free radical polymerization, which are highly desirable materials in various practical applications including tissue engineering scaffolds, separation science, bio-engineering and so on. The as-prepared MMA-HIPEs possess high thermal stability without phase separation. The textural characteristics of as-prepared composites, such as pore size and distribution, can be easily controlled by simply varying the amount of FDBC and/or dispersed phase fraction. Moreover, the influence of di-block concentration on water uptake (WU) capability of the prepared porous monoliths is explored.