Jianding Chen

Conformational changes coupled with the isotropic-anisotropic transition. Part 1. Experimental phenomena and theoretical considerations

Abstract Phase behavior and conformation characteristics were reported for poly(γ-benzyl- l -glutamate) (PBLG) in dichloroacetic acid (DCA) and a mixed solvent of CHCl3/trifluoroacetic acid (TFA). The anisotropic–isotropic transition, where intramolecular helix–coil transition was coupled, was observed for the PBLG liquid crystal solution prepared, at room temperature, with either a decrease in temperature or an increase in acid content. The information on PBLG molecular conformation provided by IR determinations indicates that in the acid mediated liquid crystal solution, the PBLG side chain may become flexible while the helix backbone remains stable prior to the helix–coil transition. Based on the molecular information gained through the experiments, the reentrant theory previously derived (Lin J. Polymer 1997;38:4837; Lin J. Polymer 1998;39:5495) was further generalized by introducing a temperature-dependent axial ratio of the Kuhn chain. The calculations carried out show an appreciable improvement in the agreement between the theory and the experimental phase diagram. The present theory also accounts, reasonably, for the temperature dependence of the PBLG order parameter observed in the experiments.

Macroporous Polymers with Aligned Microporous Walls from Pickering High Internal Phase Emulsions

A novel class of macroporous polymers, open macroporous polymers with aligned microporous void walls, were prepared by combining particle-stabilized high internal phase emulsion (Pickering HIPE) and unidirectional freezing technique. These Pickering HIPEs were prepared by utilizing poly(urethane urea)/(vinyl ester resin) nanoparticles as the sole stabilizer, and this nanoparticles also acted as building blocks for the resulting macroporous polymers. Moreover, the morphology and compression modulus of the resulting porous materials could be tuned easily. This means now Pickering-HIPE templated open-cell foams can be prepared, and this route was normally achieved with surfactant and/or chemical reaction involved.

Switchable release and recovery of nanoparticles via a Pickering-emulsion-templated porous carrier

A Pickering-emulsion-templated macroporous polymer was utilized as a novel release carrier for switchable controlled release and recovery of nanoparticles. With silica nanoparticles as stabilizers, oil-in-water Pickering high internal phase emulsions were prepared as templates to synthesize porous poly(N-isopropylacrylamide) materials with silica nanoparticles inlaid in the polymer void walls. The porous materials can effectively avoid the diffusion of silica nanoparticles when the release is undesirable, and can resorb the released nanoparticles back from the aqueous solution simply by controlling the temperature. Because a wide range of functional nanoparticles can be used to stabilize Pickering emulsions, the method developed herein provides an alternative to prepare carriers for controlled release and recovery of functional nanoparticles.

Synthesis, characterization, and antibacterial activity of yttrium(III) complexes with 2,6-pyridinedicarboxylate and pyridine

A series of metal coordination complexes of yttrium(III) containing 2,6-pyridinedicarboxylate and pyridine have been prepared with different molar ratios of yttrium(III) to 2,6-pyridinedicarboxylate in aqueous pyridine solutions, and characterized by elemental analysis, infrared spectra, nuclear magnetic resonance, and thermal analyses. The in vitro antibacterial activities of the complexes have also been investigated against microorganisms such as Gram-negative bacteria Bacillus coli and Gram-positive bacteria Staphylococcus aureus by the disc diffusion method in DMSO. When compared to previous results, the yttrium(III) complexes of 2,6-pyridinedicarboxylate and pyridine have a moderate effect on microorganisms due to the presence of the pyridine group.

Vinyl ester oligomer crosslinked porous polymers prepared via surfactant-free high internal phase emulsions

Using vinyl ester resin (VER) containing styrene (or methyl methacrylate) and vinyl ester oligomer (VEO) as external phase, Pickering high internal phase emulsions (Pickering HIPEs) having internal phase volume fraction of up to 95 vol% were prepared with copolymer particles as sole stabilizer. Polymerizing the external phase of these Pickering HIPEs led to porous polymers (poly-Pickering-HIPEs). Compared to the polystyrene- (PS-) based poly-Pickering-HIPEs which were prepared with mixture of styrene and divinylbenzene (DVB) as crosslinker, the poly-Pickering-HIPEs herein showed much higher elastic modulus and toughness. The elastic modulus of these poly-Pickering-HIPEs increased with increasing the VEO concentration in the external phase, while it decreased with increasing internal phase volume fraction. Increasing VEO concentration in the external phase also resulted in a decrease in the average void diameter as well as a narrow void diameter distribution of the resulting poly-Pickering-HIPEs. In addition, there were many small pores in the voids surface caused by the volume contraction of VER during the polymerization, which suggests a new method to fabricate porous polymers having a well-defined hierarchical pore structure.

Synergistic Effect of Copolymer Particle and Surfactant on the Morphology of Macroporous Materials Based on High Internal Phase Emulsion

The open porous materials (PolyHIPEs) based on high internal phase emulsions (HIPEs) stabilized by copolymer particles had been prepared through adding small quantity (about 0.5 wt% relative to the external phase) of cationic surfactant, cetyltrimethylammonium bromide (CTAB), into the oil (external) phase. The effect of copolymer particle concentration, surfactant concentration and CTAB position in HIPEs on the morphologies of PolyHIPEs was investigated. All these factors could tune the internal structures of the Poly- HIPEs and some of them generated pore throats on the pore wall. Obvious synergistic interaction between the negative-charged particles and cationic surfactant CTAB in HIPE was displayed: CTAB could not only adsorb on the oil-water interface competitively with the copolymer particles but also cross the interface to absorb on the particle surface, which changed the particle hydrophilicity. The further investigation on the stability of HIPE proved that the HIPEs with CTAB in the oil phase were more prone to form open porous materials after polymerizing the monomer in the external phase.

Macroporous polymers prepared via frozen UV polymerization of the emulsion-templates stabilized by a low amount of surfactant

Macroporous polymers based on high internal phase emulsions (HIPEs) possess tunable porous structures and device shapes, and these characteristics make it possible for it to be applied in many fields. However, such materials also demonstrate undesirable properties, such as their brittleness and chalkiness, due to a great amount of surfactant required (5.0–50.0%, relative to the external phase) to realize the transformation from HIPEs to macroporous polymers (polyHIPEs). Herein, O/W HIPEs stabilized by a small amount (as low as 0.1 wt%, relative to the external phase) of commercial surfactant were prepared by magnetic stirring and subsequently homogenizing, and well-defined polyHIPEs were obtained through frozen UV polymerization of these HIPEs. In this process, the prepared HIPE was squeezed out by an injector and frozen at once, which effectively prevented the coalescence of internal phase. Then a 365 nm UV light was utilized to initiate the polymerization and the temperature was kept at −20 °C in order to avoid the melting of the frozen HIPE. After the polymerization, samples, having a typical polyHIPE structure, were obtained. Besides, the original monomer, surfactant and the oil (internal phase) were respectively replaced, and well-defined polyHIPEs could still be obtained. All the results suggested that frozen UV polymerization of HIPEs was an effective and universal approach to produce polyHIPEs with a low amount of surfactant.

Synthesis of Emulsion-Templated Magnetic Porous Hydrogel Beads and Their Application for Catalyst of Fenton Reaction

The pristine Fe3O4 nanoparticle (FeNP) is supposed to be a good catalyst of Fenton processes which have shown significant potential for water purification. Herein the magnetic macroporous hydrogel beads, having an open-cell structure, were synthesized by sedimentation polymerization of pristine FeNP stabilized oil-in-water high internal phase emulsions. The effects of the FeNP amount, internal phase fraction, and the costabilizer Tween85 concentration on the structure, such as interconnecting degree, void size, and its distribution of both the surface and inner of the beads, were investigated. With a methyl orange (MO) aqueous solution passing through a chromatography column that was filled with the FeNPs loaded hydrogel beads, the efficiency of these hydrogel beads as catalyst for Fenton reaction to decompose MO in water was tested. The MO was decomposed quickly at the first hour, followed by decomposed gradually in a further 5 h, and the decomposition rate of MO could be up to 99.6% at the end of the test. Moreover, MO decomposition rate remained over 98.2% in six batches which were run in the same beads filled column. The results showed that these FeNPs loaded porous hydrogel beads were reusable and highly efficient supporter for catalysis of Fenton reaction for decomposing organic pollutants in water.

Poly(butyl methacrylate-co-methacrylic acid) Copolymers with Calcium Carbonate Supramolecular Networks

Poly (butyl methacrylate-co-methacrylic acid) copolymers/calcium carbonate (CaCO3) composites were synthesized by radical polymerization. Ca2+ cationic sites, present at the CaCO3 surface, in interaction with carboxylate groups from polymer chains structured the material, particularly above the glass transition temperature. The composites were studied by transmission electron microscopy, X-ray diffraction, and dynamic mechanical analysis. Multiplets and clusters were detected. The materials behavior is principally controlled by the methacrylic acid (MA) content in the copolymer chain and CaCO3/MA ratio. Under well-defined conditions, ionic cross-linked materials were obtained.

Polystyrene supramolecular networks based on DA-AD hydrogen bonds

Then polystyrene supramolecular networks were prepared by radical copolymerization of styrene with monomers containing donor–acceptor (DA) moieties methacrylamide (MAAM) or 2-methacrylamidopyridine (MAP). The molar percentages of MAAM and MAP in the copolymers were, respectively, 2–20% and 6–40%. The glass transition temperatures (Tgs) of these copolymers have been modeled by the Kwei equation showing secondary interactions due to intermolecular hydrogen bonds. The DA-AD association constants (K) have been calculated by 1H NMR spectroscopy of MAAM and MAP. These constants were, respectively, 6.75 and 16.75 M−1. Dynamic mechanical analyses by frequency and temperature sweep tests, were carried out in the molten state. Styrene–MAP or styrene–MAAM copolymers had higher moduli than neat polystyrene but the MAP influences the materials’ properties distinctively from the MAAM. MAP copolymers had a second G′ plateau that appeared at 150 °C, thus showing the formation of a supramolecular network.