Liyan Liang

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.

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.

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.

High thermo-responsive shape memory epoxies based on substituted biphenyl mesogenic with good water resistance

In this work, a novel epoxy monomer denoted as 3,5′-di-t-butyl-5,3′-dimethyl biphenyl diglycidyl ether (t-BuMBPDGE) was synthesized and applied into in situ composites with 3,3′,5,5′-tetramethyl-4,4′-biphenyl diglycidyl ether (TMBPDGE), accompanied with curing agent aromatic amines. 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. The samples showed good mechanical properties and could recover quickly from a second state to their initial states with a shape fixity ratio higher than 98% and shape recovery ratio higher than 99%, owing to the oriented structure and increased crosslink network density caused by the orientation of biphenyl mesogenic. The high glass transition temperatures ranging from 160 to 178 °C and good water resistance could contribute to a stable fixed shape. The water resistance is analyzed by contact angles test. The samples exhibited contact angles of 92–98 degrees, which indicated that the water resistance was apparently better than that of conventional epoxy systems.

Modification of the Properties of Polylactide/ Polycaprolactone Blends by Incorporation of Blocked Polyisocyanate

This work investigates and discusses the thermal, mechanical, thermo-mechanical properties and the morphology of solvent cast products from polylactide (PLA) and polycaprolactone (PCL), as well as their blends containing ethyl cellosolve blocked polyisocyanate (EC-bp), which was introduced as a crosslinker. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) are used to analyze the effects of the addition of EC-bp and PCL on the thermal and crystallization behaviors. The results show that the glass transition temperature (Tg) and crystallization rate is increased and decreased by the addition of EC-bp, respectively, whereas the opposite tendency is observed in the presence of PCL. Tensile testing shows much better tensile properties of the EC-bp modified blends in comparison with unmodified ones. Dynamic mechanical analysis (DMA) reveals that the storage modulus and thermal stability of the PLA/PCL blends with EC-bp are enhanced with respect to the ones without. Environmental scanning electron microscopy (ESEM) is used to characterize the morphology and evaluate the interfacial adhesion. The result demonstrates that much better dispersion (PCL domains) and homogeneity morphology is achieved for EC-bp modified blends, which indicates that the addition of EC-bp can improve the interfacial adhesion.

Synthesis and properties of biodegradable polyurethane crosslinkers from methyl ethyl ketoxime-blocked diisocyanate

AbstractA series of novel biodegradable blocked polyurethane crosslinkers (BPUCs) were synthesized from the reaction of toluene 2,4-diisocyanate (TDI), isophorone diisocyanate (IPDI), polycaprolactone (PCL), 1,1,1-trimethylolpropane (TMP), and methyl ethyl ketoxime (MEKO). Synthesis of the accurate kind of BPUCs was confirmed by Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance spectroscopy (1H NMR), and gel permeation chromatography (GPC). Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to determine the deblocking temperatures of the BPUCs. The thermal analysis revealed that both TDI- and IPDI-based BPUC had the proper initial deblocking temperature (<160 °C) and the maximum deblocking temperature (<200 °C) for practical applications. Compared to IPDI-based BPUC, the TDI-based BPUC had a lower thermal dissociation temperature and a faster deblocking rate. Hydroxyl polyurethane (HPU) was introduced to study the crosslinking effect of prepared BPUCs. The reaction proceeded at various deblocking temperatures in different curing times. It was noticed that the elastic modulus and tensile strength of the HPU sample increased whereas elongation at break decreased with the addition of BPUC in comparison with pure HPU, which suggested better interfacial adhesion due to the strong chemical reaction between the released NCO groups from BPUC and hydroxyl groups from HPU. In addition, improvement on water resistance of the BPUC modified HPU samples compared to pure HPU samples also demonstrated the good crosslinking effect of prepared BPUCs.

Synthesis and characterization of novel bisphthalonitrile resins linked by different molecular weight main-chain polybenzoxazines

ABSTRACT A series of novel type bisphthalonitriles with different molecular weight main-chain polybenzoxazines as linkages have been successfully synthesized using 4, 4′-diaminodiphenyl methane, paraformaldehyde, bisphenol A and 4-nitrophthalonitrile as initial materials. The structures were characterized by Fourier transform infrared (FT-IR) and proton nuclear magnetic resonance (1H-NMR). The formation of benzoxazine and the existence of nitrile groups were confirmed by the absorbance at 950cm−1 of benzene attached with oxazine ring and 2231 cm−1 of nitrile groups. The characteristic resonance peaks observed at about 4.52 (C-CH2-N) and 5.28 ppm (N-CH2-O) also determined the structure of benzoxazine ring. The curing behaviors were monitored by differential scanning calorimetry (DSC) and FT-IR. Two-stage polymerization mechanisms were observed according to the ring-opening of benzoxazine and the polymerization of nitrile groups catalyzed by phenolic hydroxyl groups, which generated during the curing reaction of benzoxazine. The polymerization of these bisphthalonitriles exhibited self-promoted curing behaviors. The completion of polymerization was proved by the disappearance of the band located at 950 cm−1 in FT-IR. Thermogravimetric analysis (TGA) was used to investigate the thermal stability, and the results showed that the cured polymers achieved extremely high char yield from 61.1% up to 74.2% at 800°C under nitrogen and exhibited increasing decomposition temperature as the contents of phthalonitrile groups increased, which indicated that the polymerization of phthalonitriles could improve the thermal stability.