Mangeng Lu

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.

Thermal degradation and flame retardancy of microencapsulated ammonium polyphosphate in rigid polyurethane foam

Abstract Microencapsulated ammonium polyphosphate MFAPP or VMFAPP with shell of melamine–formaldehyde or poly (vinyl alcohol)–melamine–formaldehyde resin was prepared by in situ polymerization, respectively. The flame-retardant performance of rigid polyurethane foam (PU) containing MFAPP or VMFAPP was analyzed by limiting oxygen index and UL-94 test. Thermal degradation behaviors of PUAPP, PUMFAPP and PUVMFAPP were studied using TG and TG–FTIR. Above results indicated that VMFAPP and MFAPP have better water resistance and flame retardancy compared with ammonium polyphosphate (APP) in PU composites. Flame-retardant properties of PUMFAPP and PUVMFAPP composites were rarely changed after hot water treatment. Due to better compatibility and the presence of active groups on the surface of APP, microencapsulation demonstrated a positive effect on the mechanical property of PU composites.

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.

Biodegradable, thermoresponsive PNIPAM-based hydrogel scaffolds for the sustained release of levofloxacin

A series of novel thermoresponsive biodegradable hydrogels (TBHs) was prepared from N-isopropyl acrylamide (NIPAM) and two biodegradable crosslinkers, poly(e-caprolactone) dimethacrylate (PCLDMA) and bisacryloylcystamine (BACy). The morphology, thermal behavior, swelling/deswelling kinetics, compression properties, in vitro drug delivery and biodegradation were investigated. The results indicated that the properties of the TBHs strongly depended on temperature and the feeding molar ratio of the PCLDMA to BACy components. Levofloxacin (LVF)-loaded hydrogels were prepared to explore their stimuli-responsive release process. The cumulative release profile of LVF-loaded TBHs exhibited a thermo-induced slow sustained drug release and a reduction-induced fast release. At a physiological pH, TBHs could be biodegraded slowly in glutathione (GSH) at 37 °C. Due to their homogeneous pore diameter, highly interconnected architecture, degradable chemistry and thermoresponsive properties, the TBHs developed herein are highly attractive with respect to tissue engineering scaffold applications.

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.

Effect of cellulose whisker and ammonium polyphosphate on thermal properties and flammability performance of rigid polyurethane foam

AbstractCellulose whisker (CW) is employed as a novel carbonization agent to build green and efficient intumescent flame retardant (CWAPP) with ammonium polyphosphate (APP). Due to the presence of CW, CWAPP exhibits more excellent flame retardancy compared with APP in rigid polyurethane foam (PU). PU-added CWAPP (PU/CWAPP) obtains higher LOI value than that with the same loading of APP. Results also indicate that CWAPP have better water resistance compared with APP in PU. Flame-retardant property of PU/APP is decreased remarkably after soaked in hot water. By comparison, that of PU/CWAPP is rarely changed after the same treatment. CWAPP also shows a positive effect on the mechanical property in PU, and compression strength of PU/CWAPP is higher than that of PU/APP with the same content of flame retardant.

Relationship between crosslinking structure and low dielectric constant of hydrophobic epoxies based on substituted biphenyl mesogenic units

In this work, a series of low dielectric constant hydrophobic epoxies based on substituted biphenyl mesogenic were prepared and characterized. The liquid crystalline phase structure and the crosslink density of substituted biphenyl epoxies were determined by polarized optical microscopy, wide angle X-ray diffraction measurements and dynamic storage moduli data. Relationship between crosslinking structure and dielectric and water resistance properties was discussed in our paper. The samples showed lower dielectric constants down to 2.24, owing to the oriented structure and increased crosslink network density caused by the orientation of biphenyl mesogenic, indicating a new idea to prepare low dielectric constant epoxies by introducing the mesogenic units into epoxy resins. And the comprehensive contributions of oriented structure and increased crosslink network in epoxies cured by aromatic amines, less hydroxyl groups existing in epoxies cured with anhydride and the hydrophobic methyl substituents or larger tert-butyl substituents, could afford good water resistance properties with water absorptions during 48 h at 25 °C ranging from 0.31–0.36%, which indicated that the water resistance was apparently better than that of conventional epoxy systems.

Influence of blocked polyisocyanate on the mechanical, thermal and interfacial properties of bamboo/hydroxyl-terminated polyurethane composites

In this study, chemical modification of bamboo powder (BP)/hydroxyl-terminated polyurethane (HPU) composites obtained by hot press was investigated using blocked polyisocyanate synthesized from reaction of isophorone diisocyanate with 1,1,1-trimethylolpropane (TMP) followed by addition of methyl ethyl ketoxime (MEKO). The modified surface of MEKO-blocked polyisocyanate (M-bp)-treated BP/HPU composites was identified by Fourier transform infrared spectroscopy from the appearance of CO bands absorbance and the reduction in relative intensity of OH, with respect to bamboo. The effects of M-bp as a cross-linker on the properties of the products were studied. Mechanical testing results showed that the tensile and flexural properties of the composites were improved by addition of such a cross-linker. The morphology analysis revealed that the M-bp-modified composites exhibited better compatibility and homogeneous morphologies in comparison with the unmodified composites. Moreover, the thermogravimetric analysis demonstrated that thermal resistance of the composites was enhanced by addition of M-bp. The moisture absorption characteristics of the products were also studied and discussed, because it is a major influencing factor for natural fibre composites. The results showed that better water resistance of modified composites was obtained due to stronger interfacial adhesion. Based on the findings in this work, they all indicated that the chemical modification occurred by the cross-linking effect of M-bp, which induced the strong bonds among the composite components.

Efficient red emission from poly(vinyl butyral) films doped with a novel europium complex based on a terpyridyl ancillary ligand: synthesis, structural elucidation by Sparkle/RM1 calculation, and photophysical properties

A novel efficient antenna Eu-complex Eu(TTA)2Tpy-OCH3·2H2O, based on the terpyridyl derivative 4′-(4-methoxyphenyl)-2,2′:6′,2′′-terpyridine(Tpy-OCH3) as the ancillary ligand, has been synthesized, structurally characterized, and its photophysical properties have been examined. Upon irradiation at the ligand-centered band in the range of 200–450 nm, the new Eu-complex displays bright red luminescence, irrespective of the medium. A Sparkle/RM1 calculation was utilized for predicting the ground-state geometries of this complex. Theoretical Judd–Ofelt and photoluminescence parameters, including quantum efficiency, as predicted from this model are in good agreement with the experimental values, proving the efficiency of this theoretical approach as implemented in the LUMPAC software (http://lumpac.pro.br). The kinetic scheme for modelling energy transfer processes shows that the main donor state is the ligand triplet state and that energy transfer occurs on both the 5D1 (20.7%) and 5D0 (79.3%) levels. As an integral part of this work, the synthesis, characterization, and luminescence properties of poly(vinyl butyral) (PVB) polymer films doped with the Eu-complex are also reported. After the Eu-complex Eu(TTA)2Tpy-OCH3·2H2O was doped into the PVB matrix to form the films, the PVB polymer matrix, acting as a co-sensitizer for Eu3+ ions, enhances the luminescence lifetimes and quantum efficiencies of the complex in comparison with its precursor complex. The new luminescent Eu/PVB films therefore show considerable promise for polymer light-emitting diode and active polymer optical fiber applications. To the best of our knowledge, this is the first report which studies in detail the photophysical properties of doped europium fluorescent films based on PVB as the polymer matrix.