Amperometric glucose biosensor based on sol-gel organic-inorganic hybrid material

A new type of sol-gel organic-inorganic hybrid material was developed and used for the production of biosensors. This material is composed of silica sol and a grafting copolymer of poly(vinyl alcohol) with 4-vinylpyridine. It prevents the cracking of conventional sol-gel-derived glasses and eliminates the swelling of the hydrogel. The optimum composition of the hybrid material was first examined, and then glucose oxidase was immobilized in this matrix to demonstrate its application. The characteristics of the biosensor were studied by cyclic voltammetry and chronoamperometry. The biosensor exhibited a series of good properties: high sensitivity (600 nA mmol(-1)L(-1)), short response time (11 s) and remarkable long-term stability in storage (at least 5 months). In addition, the characteristics of the second-generation biosensor with the use of tetrathiafulvalene as a mediator mere discussed.

Compatibilization effect of graft copolymer on immiscible polymer blends: 1. LLDPE/SBS/LLDPE-g-PS systems

compatibilizing effect of graft copolymer, linear low density polyethylene-g-polystyrene (LLDPE-g-PS), on immiscible blends of LLDPE with styrene-butadiene-styrene triblock copolymer (SBS) has been investigated by means of C-13 CPMAS n.m.r. and d.s.c. techniques. The results indicate that LLDPE-g-PS is an effective compatibilizer for LLDPE/SBS blends. It was found that LLDPE-g-PS chains connect two immiscible components, LLDPE and SBS, through solubilization of chemically identical segments of LLDPE-g-PS into the amorphous region of LLDPE acid PS block domain of SBS, respectively. It was also found that LLDPE-g-PS chains connect the crystalline region of LLDPE by isomorphism, with serious effects on the supermolecular structure of LLDPE. The effect of LLDPE-g-PS on the supermolecular structure of LLDPE in the LLDPE/SBS blends obviously depends on the composition of the blends, but has little dependence on the PS grafting yields of LLDPE-g-PS. (C) 1998 Elsevier Science Ltd. All rights reserved.

Gas separation with organo-soluble high performance aromatic polyimide films

An organo-soluble polyimide based on 4,4'-(1,4-phenylenedioxy)diphthalic anhydride and 2,2'-dimethyl-4,4'-methylenedianiline was synthesized by two-step polycondensation accompanied by chemical imidization. Polyimide films were prepared by spray casting onto glass substrates. The study focused on the separation of carbon dioxide (CO2) from natural gas and the enrichment of methane (CH4) from butane (C4H18). The permeability and permselectivity coefficients of these gases were determined.

Synthesis and investigation of monoesters of polymaleic acids with azo-group

A series of amphiphilic polymers, monoesters of polymaleic acid containing ate-side groups (PMAN-A(n)Me) was synthesized by the reaction of alcohol(A,Me) with polymaleic anhydride (PMAN) for Langmuir-Blodgett assembly. The effects of the length of flexible spacer in the side chain on the pi-A isotherms and LB films were investigated. The UV-Vis and infrared linear dichroism spectra showed that the ate-side groups were highly oriented in PMAN-A(6)Me LB film deposited on silica or CaF2 substrate.

Morphologies and mechanical properties of epoxy resins toughened by hydroxyl-terminated butadiene-acrylonitrile copolymer

The morphologies and mechanical properties of epoxy resins toughened by hydroxyl-terminated butadiene-acrylonitrile copolymer (HTBN) and cured with hexahydrophthalic anhydride were studied, The results show that the level of HTBN in epoxy resin, content of acrylonitrile in HTBN and curing temperature influence the morphology and then influence the mechanical properties of cured epoxy resin.

Cure processing modeling and cure cycle simulation of epoxy-terminated poly(phenylene ether ketone) .1. DSC characterization of curing reaction

The curing reaction process of epoxy-terminated poly(phenylene ether ketone) (E-PEK) with 4,4'-diaminodiphenyl sulfone (DDS) and hexahydrophthalic acid anhydride (Nadic) as curing agents was investigated using isothermal differential scanning calorimetry (IDSC) and nonisothermal differential scanning calorimetry (DDSC) techniques. It was found that the curing reactions of E-PEK/DDS and E-PEK/Nadic are nth-order reactions but not autoaccelerating. The experimental results revealed that the curing reaction kinetics parameters measured from IDSC and DDSC are not equivalent. This means that, in the curing reaction kinetics model for our E-PEK system, both isothermal and nonisothermal reaction kinetics parameters are needed to describe isothermal and nonisothermal curing processes, The isothermal and nonisothermal curing processes were successfully simulated using this model. A new extrapolation method was suggested. On the basis of this method the maximum extent of the curing reaction (A(ult)) that is able to reach a certain temperature can be predicted. The A(ult) for the E-PEK system estimated by the new method agrees well with the results obtained from another procedure reported in the literature. (C) 1997 John Wiley & Sons, Inc.

Cure processing modeling and cure cycle simulation of epoxy-terminated poly(phenylene ether ketone) .2. Chemorheological modeling

Chemorheology and corresponding models for an epoxy-terminated poly(phenylene ether ketone) (E-PEK) and 4,4'-diaminodiphenyl sulfone (DDS) system were investigated using a differential scanning calorimeter (DSC) and a cone-and-plate rheometer. For this system, the reported four-parameter chemorheological model and modified WLF chemorheological model can only be used in an isothermal or nonisothermal process, respectively. In order to predict the resin viscosity variation during a stepwise temperature cure cycle actually used, a new model based on the combination of the four-parameter model and the modified WLF model was developed. The combined model can predict the resin viscosity variation during a stepwise temperature cure cycle more accurately than the above two models. In order to simplify the establishment of this model, a new five-parameter chemorheological model was then developed. The parameters in this five-parameter model can be determined through very few rheology and DSC experiments. This model is practicable to describe the resin viscosity variation for isothermal, nonisothermal, or stepwise temperature cure cycles accurately. The five-parameter chemorheological model has also successfully been used in the E-PEK systems with two other curing agents, i.e., the diamine curing agent with the addition of a boron trifluride monoethylamine (BF3-MEA) accelerator and an anhydride curing agent (hexahydrophthalic acid anhydride). (C) 1997 John Wiley & Sons, Inc.

Melt functionalization of ethylene-propylene copolymer: Structural investigation

An ethylene-propylene copolymer (EPM) has been functionalized with acrylic acid (AA) by means of a radical-initiated melt process. Different degrees of grafting have been obtained by varying the overall composition of the reaction mixture. The influence of the grafting degree on the structure has been investigated by differential scanning calorimetry (DSC), Fourier-transform infrared analysis (FTIR), and wide-angle x-ray scattering (WAXS) techniques. The results of the structural investigations suggest that the grafting preferentially occurs onto the ethylene sequences of EPM. After acrylic acid was grafted onto EPM, the grafted AA acted as nucleation agent; it caused an increase of crystallization temperature of propylene sequences of EPM-g-AA.

H-1 nmr study on the ring opening selectivity of aromatic dianhydrides towards methanol

Several isomeric aromatic diester-diacids may appear as a result of the opening selectivity of anhydride groups towards the alcohol. H-1 n.m.r. was thus used to characterize the isomeric structure and to quantify the isomer composition. It was found that the isomer ratios quantitatively correlate with electron affinity of bridged dianhydrides and is independent of the alcohol structure used. Furthermore, the H-1 n.m.r chemical shift of bridged diester-diacids was found to be a very sensitive probe of chemical nature of bridged groups and can be used as indices of the opening selectivity. (C) 1997 Elsevier Science Ltd.

Study on the structure and miscibility of PBPI-E/PTI-E blends

The crystallization, miscibility and structure of polyimide PBPI-E/PTI-E blends were studied by DSC, DMA, NMR and fluorescence techniques, where PBPI-E is a biphenyldianhydride-based polyimide, and PTI-E is a polyimide from 4,4'-thiodiphthalic anhydride and 4,4'-oxydianiline. The results obtained show that PBPI-E/PTI-E blends are miscible at a molecular level for all the compositions studied. However, the glass transition temperature of the blends is well below the value predicted by the Fox equation, and the blends are not stable at high temperature, i.e. phase separation will occur when the blends are annealed about T-g. Moreover, the melting point T-m, differential enthalpy Delta H and spin-lattice relaxation time T-l(c) of the blends increase with the annealing time. (C) 1997 Elsevier Science Ltd. All rights reserved.

Synthesis and characterization of novel polyimides from alicyclic dianhydride

New alicyclic Polyimides (PIs) were prepared from asymmetric alicyclic dianhydride, 5-(2,5-dioxotetrahydrofuryl)-3-methyl-cyclohexane-1,2-dicarboxylic anhydride (DOCDA) and the corresponding aromatic diamines such as p-phenylenediamine, m-phenylenediamine and oxydianiline etc. by the polycondensation in N-methyl-2-pyrrolidone (NMP) followed by chemical imidization as well as one step polyimidization in m-cresol in the presence of isoquinoline as a catalyst. The resulting PIs with glass transition temperatures ranging from 220 to 328 degrees C had the inherent viscosities within the range of 0.25 similar to 1.42 dL/g. These polymers were readily soluble in aprotic polar solvents such as NMP, dimethylacetamide (DMAc), dimethylesulfoxide (DMSO), etc. Furthermore, some of the polymers showed good solubility properties to common organic solvents like tetrahydrofurane and chlorform. Also, all of these polyimide films were tough, almost colourless, and transparent.

The effect of formulated molecular weight on temperature resistance and mechanical properties in polyimide based composites

This experimental study examines the role of formulated molecular weight between crosslink sites on the temperature resistance and mechanical properties of composites based on a polyimide containing a diphenyl thioether unit (PTI). The composites are fabricated by in situ polymerization of monomer reactants (PMR) using three monomeric ingredients: bis(3,4-dicarboxyphenyl) sulfide dianhydride (TDPA); 4,4'-methylene dianiline (MDA); and the monomethyl ester of norbornene anhydride (NE). By changing monomeric molar ratio, three formulations are prepared, in which formulated molecular weight between crosslink sites varies from 1487 to 3446 g mol(-1). Unidirectional composite laminates from each formulation and T300 carbon fibres are compression moulded and cut into a series of test specimens. By measuring the glass transition temperature (T-g), Mode I interlaminar fracture toughness (G(IC)) and other mechanical properties at room and elevated temperatures, the influences of formulated molecular weight on the temperature resistance and mechanical properties of PTI-based composites are investigated.

The determination of ethylene-propylene copolymer-grafted-glycidyl methacrylate by the contact angle method

The contact angles theta of some liquids on ethylene-propylene copolymer-grafted-glycidyl methacrylate (EPM-g-GMA) were measured. The critical surface tensions r(c) of EPM-g-GMA were evaluated by the Zisman Plot (cos theta versus r(L)), Young-Dupre-Good-Girifalco plot (1 + cos theta versus 1/r(L)(0.5)) and log (1 + cos theta) versus log(r(L)) plot. The following results were obtained: the r(c) values varied significantly with the estimation methods. The critical surface tension r(c) decreased with the increase of the degree of grafting of EPM-g-GMA.

Crafting of glycidyl methacrylate onto ethylene-propylene copolymer: Preparation and characterization

Ethylene-propylene copolymer (EP) was functionalized with glycidyl methacrylate (GMA) by means of a radical-initiated melt grafting reaction. FTIR and ESCA were used to characterize the formation of EP-g-GMA copolymers. The content of GMA in EP-g-GMA was determined by using hydrochloric acid/xylene titration. Effects of concentrations of GMA and dicumyl peroxide on grafting rate were studied. It was found that contact angles of the water on surfaces of EP-g-GMA samples increased with increasing content of GMA in EP-g-GMA. The influence of the content of GMA on the crystallization structure of EP-g-GMA was investigated by DSC and WAXD. Compared with the plain EP, the crystallization temperature of propylene blocks of EP-g-GMA increased over 10 K, and the melting temperature and crystallinity decreased somewhat. Functionalization of EP led to the change of the crystal form of propylene blocks from the mixed form of alpha and beta into the alpha form. (C) 1996 John Wiley & Sons, Inc.

Compatibilization effect of graft copolymer on immiscible polymer blends .2. LLDPE/PS/LLDPE-g-PS systems

The compatibilizing effect of graft copolymer, linear low density polyethylene-g-polystyrene (LLDPE-g-PS), on immiscible LLDPE/PS blends has been studied by means of C-13 CP-MAS NMR and DSC techniques. The results indicate that LLDPE-g-PS is an effective compatibilizer for LLDPE/PS blends, and the compatibilizing effect of LLDPE-g-PS on LLDPE/PS blends depends on the PS grafting yield and molecular structure of the compatibilizers and also on the composition of the blends. It was found that LLDPE-g-PS chains connect two immiscible components, LLDPE and PS, through solubilization of chemically identical segments of LLDPE-g-PS into the noncrystalline region of the LLDPE and PS domain, respectively. Meanwhile, LLDPE-g-PS chains connect the crystalline region of LLDPE by isomorphism, resulting in an obvious change in the crystallization behavior of LLDPE. (C) 1996 John Wiley & Sons, Inc.