Yunfei Zhang

An efficient long fluorescence lifetime polymer-based sensor based on europium complex as chromophore for the specific detection of F−, CH3COO−, and H2PO4−

A novel long fluorescence lifetime europium-complexed copolymer (Eu-polymer) has been designed and synthesized via the classic free radical copolymerization reaction as an efficient fluorescent sensor for F−, CH3COO−, and H2PO4−. The anions-sensitivity of Eu-polymer was evaluated using a series of anions in DMSO solution. On binding to F−, CH3COO−, or H2PO4−, fluorescence quenching of Eu-polymer was demonstrated by an approximately 95% reduction in the fluorescence intensity, while no obvious fluorescence change could be observed in the presence of other anions. Compared with its small molecular counterpart, Eu-polymer exhibits higher sensitivity and selectivity. Most importantly, the Eu-polymer sensor can efficiently recognize and sense F− even in the presence of competitive anions, such as CH3COO− and H2PO4−, which demonstrates the ability of Eu-polymer to function as a selective fluorescence sensor for F−. The fluorescence quenching can be attributed to the strong hydrogen bonding interaction (and deprotonation interaction at high concentration for F−) between anions and the imidazole group of Eu-polymer. Due to the long fluorescence lifetime of this Eu-polymer, it can efficiently eliminate the effects of auto-fluorescence and light scattering from surrounding biological environments, so this sensor will be very significant for application in biological and environmental fields.

Efficient monochromatic red-light-emitting PLEDs based on a series of nonconjugated Eu-polymers containing a neutral terpyridyl ligand

Three novel Eu-polymers containing hole transporting units and light-emitting units in the main chain have been designed and synthesized via radical copolymerization of N-vinylcarbazole and polymerizable Eu(TTA)3vinyl-tpy, where TTA is 2-thenoyltrifluoroacetonate. The chemical structure and composition of the Eu-polymers were characterized by FTIR, UV-vis, 1H NMR, 13C NMR spectroscopy, GPC, ESI-MS, and elemental analysis. The geometry of the polymerizable monomer Eu(TTA)3vinyl-tpy was predicted using the Sparkle/PM6 model and suggested to be in a chemical environment with very low symmetry around the Eu3+ ions (C1), in agreement with the fluorescence spectrum. All Eu-polymers exhibited good solubility, as well as good thermal stability and high glass transition temperatures. The photoluminescence (PL) properties of the copolymers in solution and in the solid state were investigated in detail. Intramolecular energy transfer from the carbazole groups to the europium complexes occurred even in diluted solutions. The efficiency of this process also depended on the composition of the Eu-polymers. In the solid state, emission from the carbazole groups was suppressed and the absorbed excitation energy was transferred effectively to the europium complexes in the Eu-polymers. Most importantly, the EL performances of eight pure red-emission PLEDs based on P1, P2, and P3 as the emitting layer have been studied in detail. Bright electroluminescence with a maximum luminance of 68.2 cd m−2 from the double-layer devices of P1 was demonstrated. Although the EL performance was only the third-best among those of the Eu-chelated polymers reported so far, to the best of our knowledge, this is the first example of electroluminescent devices of Eu-polymers based on tpy as a neutral ligand. These results illustrate the potential application of polymerizable tpy ligands in high performance EL Eu-chelated polymers.

Synthesis of copolymers with cyclodextrin as pendants and its end group effect as superplasticizer

In this paper, the efficient approach for the synthesis of β-cyclodextrin (CD) based functional monomers was described. Based on the monovinyl β-CD monomer (GMA-EDA-CD), a new type poly(AA-co-GMA-EDA-CD) (PCDs) copolymer bearing pendent CD groups was synthesized and used as superplasticizer. Their chemical compositions were characterized by FT-IR, NMR, MALDI-TOF and GPC. The effects of PCDs on dispersion and adsorption in cement mortars were detailed discussed. The results indicated that PCD copolymers behaved excellent dispersion ability and strong retarding effect. PCD2 with molar ratio (%) for monomer (AA:GMA-EDA-CD=80:20) had the best dispersion and dispersion maintaining abilities, which were mainly attributed to the synergistic effects of steric hindrance and electrostatic repulsive force, and the retarding effect of PCD copolymers resulted from steric hindrance repulsion of CD pendants and the large number of hydroxyl groups, which affected the hydration reaction of cement.

Pseudo-graft polymer based on adamantyl-terminated poly(oligo(ethylene glycol) methacrylate) and homopolymer with cyclodextrin as pendant: its thermoresponsivity through polymeric self-assembly and host–guest inclusion complexation

A series of well-defined adamantyl-terminated thermally responsive copolymers (Ad-POEGMAs) were synthesized by atom transfer radical polymerization (ATRP), in which 2-(2-methoxyethoxy) ethyl methacrylate (MEO2MA) and oligo(ethylene glycol) methacrylate (OEGMA) served as the thermosensitive building blocks. Moreover, cyclodextrins (CDs) as bulky pendant grafted polymers (PGCD) were synthesized by homopolymerization of aminoethyl methacrylate β-cyclodextrin (GCD). The thermal-responsive behaviors were investigated by a combination of 1H NMR, UV-vis spectroscopy, dynamic light scattering (DLS), and transmission electron microscopy (TEM). In comparison to other thermal-responsive copolymers based on POEGMAs, Ad-POEGMAs exhibited unusual thermally induced aggregation processes. The Ad group assembled and POEGMA chains associated to produce stable water-soluble nano-aggregates, followed by a rearrangement process at the second thermal transition. Moreover, it was found that a noncovalently connected supramolecular pseudo-graft polymer was formed via inclusion complexation in aqueous solution. This pseudo-graft polymer underwent a reversible temperature-induced transition from solution to micelle under suitable conditions. The cyclodextrin (CD) moiety attached to the main chain played two roles. As supramolecular host moieties, CDs formed inclusion complexes with guest-ended polymers, leading to graft-like polymers. As bulky hydrophilic moieties, CDs stabilized the micelles induced by the coil-to-globule transition of POEGMA segments.

Crystallization behavior of stable urea formaldehyde resin dispersed by polyvinyl alcohol

A series of stable polyvinyl alcohol (PVA) modified urea–formaldehyde (UF) resins have been synthesized by traditional alkaline–acid–alkaline three-step reaction and characterized by Fourier transformation infrared spectrophotometer (FTIR), scanning electronic microscope (SEM), polarization optical microscope (POM) and X-ray diffraction (XRD). In addition, some neat or modified UF resin-impregnated filter papers were prepared and used to test the effects of PVA on the tensile strength and water resistance of the UF resins. The results of formaldehyde titration analysis and viscosity measurement exhibited that when the mass ratio of PVA/U (urea as a fixed value) was increased, the free formaldehyde content of the UF resins was decreased, and the storage stability of the UF resin was improved. Besides, the SEM and POM results showed that the crystallite regions related to the colloidal particle of the UF resin became more uniform by incorporation of proper amount of PVA (with mass ratio of PVA/U around 0.0050). In addition, the result of XRD analysis indicated that the cured neat or PVA-modified UF resin with relatively high mole ratio of formaldehyde to urea has amorphous structure. The results of the mechanical testing showed that PVA can be used to strengthen and toughen the UF resin and the water resistance evaluation indicated that the UF resin modified with more PVA may have lower water resistance.

Low formaldehyde emission urea-formaldehyde resins modified by 2,4,6-trimethylolphenate and physical properties of its impregnated papers

The objective of this study is using 2,4,6-trimethylolphenate (TMP) as modifier to prepare stable TMP-Urea-Formaldehyde resins (TMPUF) with low formaldehyde emission and using TMPUF to improve mechanical properties and water resistance of the common filter paper. The prepared TMPUF was characterized by IR, DSC and POM. The results indicated that as the mass ratio of TMP/U was increased, the free formaldehyde concentration of the TMP modified UF resins was decreased. Curing temperature of TMPUF was increasing with the decreasing of free low formaldehyde and POM analysis showed that the crystalline structure of TMPUF is destroyed with the adding of TMP. In addition, mechanical properties, thermal stability and water absorption of TMUF impregnated papers have been studied. The results showed that both mechanical properties and water absorption of TMPUF impregnated papers can be improved in the experimental range. However, all TMPUF impregnated paper shows little difference in thermal stability. These results indicated that TMP as a kind of phenol-formaldehyde intermediate is a useful alternative to formaldehyde and phenol to reduce environmental pollution. This work provides a method of preparing stable TMPUF adhesives with low formaldehyde emission used for wood adhesives and paper impregnating applications.