Hongting Pu

A facile method for the fabrication of vinyl functionalized hollow silica spheres

In this paper, we adopt a facile method to prepare vinyl functionalized hollow silica spheres. Vinyl functionalized silica shells were coated on positively charged polystyrene particles by hydrolysis and condensation of vinyltriethoxysilane (VTES), the polystyrene cores were dissolved subsequently in the same medium to form monodispersed vinyl functionalized hollow silica spheres. Neither additional dissolving nor a calcination process is necessary to remove the polystyrene cores. Transmission electron microscopy (TEM), FT-IR analysis, TGA and porosity measurements were used to characterize the monodispersed vinyl functionalized hollow silica spheres.

π-conjugated sulfonium-based photoacid generators: an integrated molecular approach for efficient one and two-photon polymerization

The cationic photoinitiating abilities of a series of ‘push–pull’ sulfonium-based photoacid generators (PAGs) have been investigated. In this linear π-conjugated series, a 4-N,N-diphenylaminostilbene subunit is associated with different types of sulfonium substituents, which are connected to the stilbene moiety either in the 4′ position or in the 3′ position. This para-to-meta substitution effect leads to a strong increase of the quantum yield for acid generation with a maximum value of ca. 0.5. Such a positioning effect has a strong influence on the efficiency of the S–C bond cleavage. A detailed photolysis mechanism has been proposed. In contrast to commercially available sulfonium salts, these highly reactive π-conjugated PAGs all exhibit large absorption in the visible range as well as large two-photon absorption cross-sections (δmax > 600 GM) in the near-infrared region. As a consequence, efficient one and two-photon polymerization reactions are observed at 405 nm and 800 nm, respectively, using typical monomers such as cyclohexene oxide, n-butyl vinyl ether or SU-8 photoresists. By the fabrication of well resolved two-dimensional microstructures, we finally demonstrate the potential use of these new generation PAGs in the fields of one and two-photon lithography.

Crosslinked polybenzimidazole via a Diels–Alder reaction for proton conducting membranes

The crosslinking of polybenzimidazole (PBI) is a potential strategy to improve the mechanical properties and dimensional stability of acid-doped membranes, as well as to retain additives in the membranes. An effective method to prepare crosslinked PBI with a well-defined structure via a Diels–Alder reaction between vinylbenzyl functionalized PBI (PBI–VB) and α,α′-difurfuryloxy-p-xylene (DFX) is proposed. The chemical structure of PBI–VB is confirmed by FTIR and 1H NMR. The model reaction of styrene and DFX is employed to clarify the crosslinking reaction of PBI and DFX. During the crosslinking process, three kinds of chemical reaction may happen. The first is a Diels–Alder reaction of DFX with the vinyl groups of PBI–VB. The second is the self-polymerization of vinyl groups. The third is the grafting of difuran groups via a Diels–Alder reaction. The first two reactions contribute the most to the crosslinking of the PBI membrane. With the addition of DFX, there is competition between these two kinds of crosslinking reactions. When the feed ratio of DFX is below 20%, the tensile strength of the crosslinked membranes increases with increasing content of DFX. The crosslinking of the membrane is mainly a results of Diels–Alder reactions. When the feed ratio of DFX exceeds 20%, the tensile strength decreases slightly. Besides the crosslinking via Diels–Alder reactions, the crosslinking of the membrane is also contributed by the self-polymerization of vinyl groups and the grafting of difuran groups. The crosslinked PBI membrane exhibits improved mechanical strength, higher physical and chemical stability, as well as higher phosphoric acid (PA) retention ability. After doping with PA, the crosslinked membrane exhibits good proton conductivity over a temperature range of 60 to 180 °C.

Design of D–π–A type photoacid generators for high efficiency excitation at 405 nm and 800 nm

New sulfonium salts with diphenylamino asymmetrically substituted stilbene as a D-π-A conjugated system have been synthesized. The resulting photoacid generators exhibit a highly efficient acid photogeneration process by either one-photon 405 nm or two-photon 800 nm excitation.

Two-photon lithography in visible and NIR ranges using multibranched-based sensitizers for efficient acid generation

We investigated methodically the one- and two-photon absorption properties of a series of multibranched triphenylamine-based chromophores incorporating 4-(methylthio)styryl fragments as external substituents. Some relevant structure–property relationships relative to these highly fluorescent compounds have been derived based on emission anisotropy measurements, quantum chemical calculations and the use of the exciton coupling theory. Even though branching effects lead to a cooperative enhancement of the two-photon absorption (2PA), all compounds exhibit relatively low-to-moderate 2PA cross-sections (δ ≤ 100 GM) in the NIR region. However, the ‘so-called’ one-photon resonance enhancement effect leads to a remarkable increase of δ by more than one order of magnitude in the visible range. This strong 2PA ability has been associated with an efficient photosensitization of iodonium salt to elaborate a new bicomponent photoacid generator, which is readily two-photon activable at 532 nm. In the visible range, the strong enhancement of the efficiency of the two-photon induced polymerization is clearly demonstrated as compared with that observed in the NIR region.

Dendritic amphiphile mediated porous monolith for eliminating organic micropollutants from water

Few adsorbents with a macroscopic size can combine well with a 3D microscopically well-tailored surface. Herein, we show that a dendritic amphiphile can directly lead to such an adsorbent, which can simultaneously eliminate anionic dyes, anionic surfactants and hydrophobic polycyclic aromatic hydrocarbons (PAHs) from water.

Photochromism-based detection of volatile organic compounds by W-doped TiO2 nanofibers.

W-doped TiO(2) nanofibers with various compositions (W/Ti: 2-8%) were fabricated by the electrospinning method from respective precursor solutions containing tungsten(V) pentaethoxide, titanium tetraisopropoxide (TTIP), and polyvinylpyrrolidone (PVP), followed with calcination at 550 °C. Morphological and structural characteristics of these nanofibers were studied with SEM, XRD and XPS. W-doping inhibited the crystal growth and anatase-to-rutile transformation of TiO(2) nanofibers. W-doped TiO(2) nanofiber mats showed good photocatalytic oxidation abilities for acetone. Obvious color change from white to blue of mats during the photocatalysis process can be detected by naked eyes, which provides a good way in detection of pollutants in indoor air, especially for the volatile organic compounds (VOCs).

Polymerization behaviors and polymer branching structures in ATRP of monovinyl and divinyl monomers

Polymerization behaviors and polymer branching structures in atom transfer radical polymerizations of styrene with 1,6-bismaleimidohexane (BMIH), tri-ethylene glycol dimethacrylate (tri-EGDMA) and divinylbenzene (DVB) as the branching agents have been studied, the mole ratio of monomer to branching agent is 30/1.0. Their polymerization behaviors are quite different because of the different levels of interaction between styrene and the branching agents. The charge transfer complex effect between BMIH and styrene causes core-formation. The DVB system exhibits the slowest evolution of branching because there is no interaction between styrene and DVB. The branching structure indicator b(g′ = gb) from the Zimm branching factor at the same molecular weight proves that polymers formed in the tri-EGDMA and DVB systems are randomly branched molecules because tri-EGDMA and DVB were randomly distributed in their primary chains, while the BMIH system contained randomly branched molecules besides the star-like molecules due to the subsequent coupling reactions between the branched molecules after core-formation.

A multifunctional azobenzene-based polymeric adsorbent for effective water remediation

The efficient removal of trace carcinogenic organic pollutants, such as polycyclic aromatic hydrocarbons (PAHs) and ionic dyes, from water is an important technical challenge. We report a highly effective recyclable multifunctional azobenzene (AZ)-based silica-supported polymeric adsorbent which can simultaneously remove both PAHs and anionic dyes from water to below parts per billion (ppb) level based on multiple interactions such as the hydrophobic effect, π–π stacking and electrostatic interactions, thus providing a new strategy for designer water remediation materials.

Orientation of LDPE crystals from microscale to nanoscale via microlayer or nanolayer coextrusion

The microlayer or nanolayer coextrusion of hundreds or thousands of alternating low density polyethylene (LDPE)/polystyrene (PS) microlayers or nanolayers were used to study the orientation of LDPE crystals in the confined quasi-two-dimensional or two-dimensional space. The clear and continuous layer structures from microscale to nanoscale can be found in SEM images. The morphology evolution of LDPE crystals in the confined microlayer or nanolayer can be varied from 3D spherulites, 2D spherulites, stacked edge-on lamellar, to single edge-on lamellar. Due to the orientation of the LDPE crystals, the tensile strength of the films increases obviously when the layer thickness reduces to nanoscale. The 2D small angle X-ray scattering (SAXS) patterns can reflect the average degree of orientation of LDPE in the confined layers. The stacking of LDPE lamellae is suppressed in interlamination and oppositely in parallel to the extrusion direction. The specific orientation function f can be calculated from the patterns. The infrared dichroism further confirms the mutation of the orientation of LDPE crystals from microscale to nanoscale in the confined space.