Spectrophotometric determination of flucythrinate (synthetic pyrethroid) using phenylhydrazines

Three spectrophotometric methods are described for determining flucythrinate, based on formation of coloured compounds when one of the hydrolysed products of flucythrinate is condensed with 2,4-dinitrophenylhydrazine (2,4-DNPH), 4-nitrophenylhydrazine (4-NPH) or 2,4,6-trinitrophenylhydrazine (2,4,6-TNPH) in the presence of methanolic potassium hydroxide. These coloured compounds absorb strongly at 465 nm (2,4-DNPH), 540 nm (4-NPH) and 485 nm (2,4,6-TNPH). The methods are applicable over the range 0.1-8.0 mug/ml for 2,4-DNPH, 0.5-6.5 mug/ml for 4-NPH and 0.1-6 mug/ml for 2,4,6-TNPH. The methods are rapid, sensitive and selective and can be used for microdetermination of flucythrinate in a commercial formulation, water, grains and crop samples.     

Determination of phenol in landfill leachate by using microchip capillary electrophoresis with end-channel amperometric detection

Phenol, 2,4-dichlorophenol (2,4-DCP), and 2,4,6-trichlorophenol (2,4,6-TCP) were baseline separated by using a homemade microchip CE with an end-channel amperometric detector where a 50 microm Pt microdisk working electrode (WE) and a Pt cathode were integrated onto the microchip itself. Separation parameters such as injection time and voltage, pH of the buffer, online pretreatment condition for WE, reproducibility, and detection potential were investigated. Under the selected separation conditions, the linear ranges for phenol, 2,4-DCP, and 2,4,6-TCP were 2-200, 4-400, and 4-400 microM, respectively. The LODs were 0.4, 0.5, and 0.7 microM for phenol, 2,4-DCP, and 2,4,6-TCP, respectively (S/N = 3). The standard addition method was successfully applied to the analysis of landfill leachate samples and the concentration of phenol in the landfill leachate samples was measured to be 0.32 and 0.21 mM, respectively. The recoveries were in the range of 85-103% and corresponding RSDs were less than 5.5%.     

Structure of chlorinated poly(vinyl chloride). XII. Configuration and reactivity of low-molecular-weight models of poly(vinyl chloride) in the course of chlorination

The chlorination of poly(vinyl chloride) (PVC) was investigated by means of low-molecular-weight models of PVC—a dimer and trimer of PVC, viz., 2,4-dichloropentane (2,4-DCP) and 2,4,6-trichloroheptane (2,4,67-TCH). Chlorinations of stereoisomeric mixtures of 2,4-DCP and 2,4,6-TCH have revealed that the d,1 form of 2,4-DCP (syndio-2,4-DCP) is more reactive in the chlorination than the meso form of 2,4-DCP (iso-2,4-DCP), while in the case of the chlorination of 2,4,6-TCH the reactivity of stereoisomers decreases in the order iso-> hetero->syndio-2,4,6-TCH; consequently, analogous structures of stereoisomers of 2,4-DCP and 2,4,6-TCH react in a reverse order and not in the same one. The qualitative order of reactivities of stereoisomers may be correlated formally with the magnitude of their dipole moments. The reactivity of stereoisomers of 2,4-DCP and 2,4,6-TCH decreases with increasing dipole moment.     

Preparation and reactions of 1,3-diphosphacyclobutane-2,4-diyls that feature an amino substituent and/or a carbonyl group

The preparation and properties of a 1-amino-1,3-diphosphacyclobutane-2,4-diyl and a 1-benzoyl-1,3-diphosphacyclobutane-2,4-diyl, which can be regarded as functionalized cyclic biradical derivatives, were investigated. Hydrolysis of 1-diisopropylamino-3-methyl-2,4-bis(2,4,6-tri-tert-butylphenyl)-1,3-diphosphacyclobutane-2,4-diyl (7), which is formed by reaction of Mes*C[triple chemical bond]P (4; Mes*=2,4,6-tBu(3)C(6)H(2)) with lithium diisopropylamide and iodomethane, resulted in ring-opening of the 1,3-diphosphacyclobutane-2,4-diyl skeleton, as well as de-aromatization of one of the Mes* rings. 3-Oxo-1,3-diphosphapropene 8 and 7-phosphabicyclo[4.2.0]octa-1(8),2,4-triene 9 were the resultant products, and these were subsequently characterized. Isomerization and oxidation of 7 occurred in the presence of TEMPO (2,2,6,6-tetramethyl-1-piperidinoxy) to give the first example of a cyclic dimethylenephosphorane derivative, namely 3-oxo-1,3-diphospha-1,4-diene 10. 1-Benzoyl-3-tert-butyl-2,4-bis(2,4,6-tri-tert-butylphenyl)-1,3-diphosphacyclobutane-2,4-diyl (12) was isolated and characterized from the reaction of 4 with tert-butyllithium and benzoyl chloride. Compound 12 was subsequently heated and underwent rearrangement of the benzoyl group and ring-expansion to afford 1-oxo-1H-[1,3]diphosphole 13. Reaction of 4 with lithium diisopropylamide and benzoyl chloride afforded the 2H-[1,2,4]oxadiphosphinine 15, which was probably formed through the 1,3-diphosphacyclobutane-2,4-diyl intermediate 14. Thermolysis of 15 afforded 1-oxo-1H-[1,3]diphosphole 16 in an Arbuzov-type rearrangement.     

New perthiophosphonic acid anhydrides and the direct indication of the dimer-monomer equilibrium. NMR and X-Ray Studies

New perthiophosphonic acid anhydrides (R-PS₂)_n with R = 2,4,6-tri-iso-propylphenyl and 2,4-di-tert-butyl-6-methylphenyl have been prepared. For the latter case, the isolation of the monomer (n = 1), the 2,4-di-tertbutyl-6-methylphenyl-dithioxophosphorane, and both dimers (n = 2), cis- and trans-2,4-bis(2,4-di-tertbutyl-6-methylphenyl)-2, 4-dithioxo-1, 3, 2, 4-dithiadiphosphetane, has been determined. The new cis and trans dithiadiphosphetanes and dithioxophosphoranes as well as the known compounds (2,4,6-trimethylphenyl-PS₂)₂ and 2,4,6-tri-tert-butylphenyl-PS₂ are characterized by solution and high resolution solid-state ³¹P and ¹³C NMR spectroscopy. The existence of a dimer-monomer equilibrium is directly proved by 2D exchange ³¹P NMR spectroscopy. It is shown that the reaction of the monomer with methanol is faster than the reaction of the dimer with methanol.     

Adsorption of phenols from contaminated water through titania-silica mixed imidazolium based ionic liquid: Equilibrium,kinetic and thermodynamic modeling studies

The present study describes the synthesis and characterization of titania-silica mixed imidazolium based ionic liquid (Ti-Si-IL) as well as evaluation of its adsorption behavior towards the 2,4-dinitrophenol (2,4-DNP) and 2,4,6-trichlorophenol (2,4,6-TCP). Synthesized Ti-Si-IL adsorbent was characterized by Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), BET surface area Brunauer-Emmett-Teller (BET), thermogravimetric analysis (TGA) and elemental analysis (CHN). The adsorption of 2,4-DNP and 2,4,6-TCP on Ti-Si-IL was investigated systematically by evaluating the effects of adsorbent dosage, initial pH, contact time and temperature. Satisfactory adsorption 95% and 65% for 2,4-DNP and 2,4,6-TCP was observed at pH 4 and 6, respectively. The kinetic results for 2,4-DNP and 2,4,6-TCP on Ti-Si-IL indicated that the kinetic data follows pseudo-second-order model (R² = 0.9985 and 0.9750, respectively). Adsorption isotherms were fitted well by the Langmuir model for 2,4-DNP (q_m = 44.64 mg g^?1 at 318 K) and Freundlich model for 2,4,6-TCP (K_F = 0.63 mg g^?1 at 318 K). The +ΔH° and -ΔG° values demonstrated that the adsorption of 2,4-DNP was endothermic and spontaneous in nature. While the -ΔH° and +ΔG° values for 2,4,6-TCP adsorption demonstrated exothermic and comparatively nonspontaneous. During the removal process, the role of different functional groups, cyclic structure was monitored and found that the ionic property as well as π-π interactions of host molecules played important role in the extent of adsorption.     

Dispersive liquid–liquid microextraction of five chlorophenols in water samples followed by determination using capillary electrophoresis

Dispersive liquid–liquid microextraction (DLLME) coupled with CE was developed for simultaneous determination of five types of chlorophenols (CPs), namely 2‐chlorophenol (2‐CP), 4‐chlorophenol (4‐CP), 2,4‐dichlorophenol (2,4‐DCP), 2,6‐dichlorophenol (2,6‐DCP), and 2,4,6‐trichlorophenol (2,4,6‐TCP) in water samples. Several parameters affecting DLLME and CE conditions were systematically investigated. Under the optimized DLLME‐CE conditions, the five CPs were separated completely within 7.5 min and good enrichment factors were obtained of 40, 193, 102, 15, and 107 for 4‐CP, 2,4,6‐TCP, 2,4‐DCP, 2‐CP, and 2,6‐DCP, respectively. Good linearity was attained in the range of 1–200 μg/L for 2,4,6‐TCP, 2,4‐DCP, 2−300 μg/L for 4‐CP and 2‐CP, and 1−300 μg/L for 2,6‐DCP, with correlation coefficients (r) over 0.99. The LOD (S/N = 3) and the LOQ (S/N = 10) were 0.31−0.75 μg/L and 1.01−2.43 μg/L, respectively. Recoveries ranging from 60.85 to 112.36% were obtained with tap, lake, and river water spiked at three concentration levels and the RSDs (for n = 3) were 1.31–11.38%. With the characteristics of simplicity, cost‐saving, and environmental friendliness, the developed DLLME‐CE method proved to be potentially applicable for the rapid, sensitive, and simultaneous determination of trace CPs in complicated water samples.     

In situ encapsulation of laccase in nanofibers by electrospinning for development of enzyme biosensors for chlorophenol monitoring

A biosensor based on Trametes versicolor laccase (Lac) was developed for the determination of phenolic compounds. The biosensor was prepared by in situ electrospinning of a mixture of polyvinyl alcohol (PVA), Lac, PEO-PPO-PEO (F108) and gold nanoparticles (Au NPs), where F108 was used as an enzyme stabilizing additive and Au NPs was used to enhance the conductivity of the biosensor. Laser confocal scanning microscopy and electrochemical impedance spectroscopy proved that the enzyme was successfully encapsulated into the electrospun nanofibers. Under the optimal conditions, the lowest detection limit was found to be 0.04 μM (S/N = 3) for 2,4-DCP and the highest detection limit was found to be 12.10 μM for 4-CP. The sensitivity of the biosensor obtained in the linear range for chlorophenols followed the sequence 2,4-dichlorophenol (2,4-DCP) > 2,4,6-trichlorophenol (2,4,6-TCP) > 4-chlorophenol (4-CP). The sensing performance for chlorophenols was attributed to the suitable electrochemical interface of PVA/F108/Au NPs/Lac, resulting from biocompatibility, a high surface area-to-volume ratio (10.42 m(2) g(-1)) and superior mechanical properties of the electrospun nanofibers. The biosensor exhibited good repeatabilities of 7.6%, 2.8% and 9.0% (R.S.D.) and reproducibilities of 14.9%, 10.4% and 13.7% (R.S.D.) for 4-CP, 2,4-DCP and 2,4,6-TCP, respectively. Lac retained 65.8% of its initial activity after a 30-day storage period.     

Regiochemically flexible substitutions of di-, tri-, and tetrahalopyridines: the trialkylsilyl trick

[reactions: see text] 2,4-Difluoropyridine, 2,4-dichloropyridine, 2,4,6-trifluoropyridine, 2,4,6-trichloropyridine and 2,3,4,6-tetrafluoropyridine react with standard nucleophiles exclusively at the 4-position under halogen displacement. However, the regioselectivity can be completely reversed if a trialkylsilyl group is introduced in the 5-position of the 2,4-dihalopyridines or in the 3-position of the 2,4,6-trihalopyridines or 2,3,4,6-tetrahalopyridine. Then only the halogen most remote from the bulky silyl unit (at the 2-position in the case of the 2,4-halopyridines, at the 6-position with the other substrates) gets involved in the exchange process. After removal of the silyl protective group the nucleophile is invariably found to occupy the nitrogen-neighboring position.     

Microbial synthesis and characterization of polyhydroxyalkanoates with fluorinated phenoxy side groups from Pseudomonas putida

Microbial poly(3-hydroxyalkanoates) (PHAs) with fluorinated phenoxy side groups were produced by Pseudomonas putida when fluorophenoxyalkanoic acids were used as carbon sources. 11-(2-Fluorophenoxy)undecanoic acid (2FPUDA), 11-(3-fluorophenoxy)undecanoic acid (3FPUDA), 11-(4-fluorophenoxy)undecanoic acid (4FPUDA), 11-(2,4-difluorophenoxy)undecanoic acid (2,4DFPUDA), 11-(2,4,6-trifluorophenoxy)undecanoic acid (2,4,6TFPUDA), and 11-(2,3,4,5,6-pentaflurophenoxy)undecanoic acid (2,3,4,5,6PFPUDA) were used as carbon sources in the present study. When cells were grown with 2,4DFPUDA, the production of homo poly(3-hydroxy-5-(2,4-difluorophenoxy)pentanoate) was confirmed by NMR and GC/MS analyses. Fluorine atoms inserted into the side chain of the PHA dramatically affected its physical properties. In marked contrast to medium chain length (MCL) PHA, this fluorinated PHA was opaque, cream colored, and possessed greater crystallinity and a higher melting point (∼100 °C) than did the other MCL PHAs. Surface contact angle evaluation revealed that the PHA with two fluorine atoms possessed water-shedding properties. The number of substituted fluorine atoms in the carbon source affected cell growth and difluorine-substituted phenoxyalkanoic acids reduced cell growth, and polymer production compared to non-substituted phenoxyalkanoic acids. No polymeric materials were obtained using either 2,4,6TFPUDA or 2,3,4,5,6PFPUDA.     

Rerouting nucleophilic substitution from the 4-position to the 2- or 6-position of 2,4-dihalopyridines and 2,4,6-trihalopyridines: the solution to a long-standing problem

2,4-Difluoro-, 2,4,6-trifluoro-, and 2,3,4,6-tetrafluoropyridine undergo nucleophilic substitution preferentially if not exclusively at the 4-position. However, after the introduction of a trialkylsilyl group at C-3 or C-5, the halogen at the 6-(2-)position is displaced selectively. This synthetically valuable regiocontrol can also be realized with other halopyridines such as 2,4-dichloro- and 2,4,6-trichloropyridine.     

Field‐amplified sample injection combined with capillary electrophoresis for the simultaneous determination of five chlorophenols in water samples

A sensitive method of CZE‐ultraviolet (UV) detection based on the on‐line preconcentration strategy of field‐amplified sample injection (FASI) was developed for the simultaneous determination of five kinds of chlorophenols (CPs) namely 4‐chlorophenol (4‐CP), 2‐chlorophenol (2‐CP), 2,4‐dichlorophenol (2,4‐DCP), 2,4,6‐trichlorophenol (2,4,6‐TCP), and 2,6‐dichlorophenol (2,6‐DCP) in water samples. Several parameters affecting CZE and FASI conditions were systematically investigated. Under the optimal conditions, sensitivity enhancement factors for 4‐CP, 2‐CP, 2,4‐DCP, 2,4,6‐TCP, and 2,6‐DCP were 9, 27, 35, 43, and 43 folds, respectively, compared with the direct CZE, and the baseline separation was achieved within 5 min. Then, the developed FASI‐CZE‐UV method was applied to tap and lake water samples for the five CPs determination. The LODs (S/N = 3) were 0.0018–0.019 µg/mL and 0.0089–0.029 µg/mL in tap water and lake water, respectively. The values of LOQs in tap water (0.006–0.0074 µg/mL) were much lower than the maximum permissible concentrations of 2,4,6‐TCP, 2,4‐DCP, and 2‐CP in drinking water stipulated by World Health Organization (WHO) namely 0.3, 0.04, and 0.01 µg/mL, respectively, and thereby the method was suitable to detect the CPs according to WHO guidelines. Furthermore, the method attained high recoveries in the range of 83.0–119.0% at three spiking levels of five CPs in the two types of water samples, with relative standard deviations of 0.37–8.58%. The developed method was proved to be a simple, sensitive, highly automated, and efficient alternative to CPs determination in real water samples.     

在饮水中典型溶解性有机氮酪氨酸氯化生成氯仿的机理分析

饮用水氯化消毒可以有效杀灭细菌, 但同时会产生危害人体健康的消毒副产物(DBP). DBP生成机理研究是有效控制DBP的前提. 溶解性有机氮(DON)是DBP的重要前体物, 选取典型DON-丙氨酸(Ala)、苯丙氨酸(Phe)和酪氨酸(Tyr)作为氯仿(CF)等DBP的前体物, 研究三种氨基酸(AA)的耗氯量和CF产率; 同时考察了Tyr氯化中间产物2,4,6-TCP的氯化特性和CF产率; 采用GC/MS扫描和前线轨道理论验证, 探讨了CF的主要生成路径. 研究发现, 在同等氯化反应条件下, 由于侧链基团的不同, Tyr的耗氯量以及CF产率都明显高于Ala和Phe, 从而说明Tyr确实是一种重要的CF前体物质. CF的主要生成路径为Tyr→ 4-MCP → 2,4-DCP → 2,4,6-TCP → CF. 氯胺消毒工艺可有效控制CF的生成, 并能减少2,4,6-TCP的产生, 但不能确保饮用水的生物安全性. 氯化消毒之前将Tyr等重要前体物去除可能是控制CF等DBP更加有效的措施.     

Synthesis of phosphorus ylides bearing a P-H bond from a kinetically stabilized 1,3,6-triphosphafulvene

In mixing 2,4,6-tris(2,4,6-tri-tert-butylphenyl)-1,3,6-triphosphafulvene with alkyllithium compounds and acetic acid, both of nucleophilic alkylation and electrophilic protonation occurred at the exo sp2-phosphorus atoms to afford [2,4-bis(2,4,6-tri-tert-butylphenyl)-1,3-diphosphacyclopentadienylidene](alkyl)(2,4,6-tri-tert-butylphenyl)phosphoranes which are phosphorus ylides that bear a P-H bond. A phosphorus ylide bearing both P-H and P-F bonds was obtained by reaction of 2,4,6-tris(2,4,6-tri-tert-butylphenyl)-1,3,6-triphosphafulvene with hydrogen tetrafluoroborate, and the structure was determined by X-ray crystallography. Both P=C double bond and P(+)-C(-) zwitterionic character was indicated by the metric parameters. The isolated phosphorus ylide bearing a P-H bond, [2,4-bis(2,4,6-tri-tert-butylphenyl)-1,3-diphosphacyclopentadienylidene](2,4,6-tri-tert-butylphenyl)phosphorane, showed no isomerization by H-migration to the corresponding phosphinodiphospholes, probably due to the pi-accepting ability of the unsaturated PC bonds and aromaticity of the C3P2 ring. The ylide structure and aromaticity of 2,4-diphosphacyclopenta-2,4-dienylidenephosphorane was characterized by theoretical calculations. In addition, the regioselective protonation of the lithiated phosphinodiphospholes generated from the 1,3,6-triphosphafulvene is discussed.     

The x-ray structure determinations and semiempirical PM3 calculations of two chloro(piperidyl)cyclotri(phosphazenes)

Single crystals of 2,4,6,6-tetrachloro-2,4-bis(piperid-yl)cyclotri(phosphazene) ( 1a ) and of 2,4,6-trichloro-2,4,6-tris(piperidyl)cyclotri(phosphazene) ( 2a ) were grown from petroleum ether solution. The structures of both compounds were determined by single-crystal X-ray diffraction analyses. Compound 1a crystallizes in the monoclinic space group P 2₁/n with Z = 4 and unit cell dimensions a = 9.3994(4), b = 19.204(3), c = 11.5664(4) Å, and β = 108.718(4)°. Compound 2a crystallizes in the triclinic space group P 1 with Z = 4 and unit cell dimensions a = 12.8289(2), b = 13.8856(2), c = 14.63810(10) Å, and α = 100.7621(5), β = 91.0094(2), γ = 113.9757(6)°. The experimentally obtained structural parameters for the covalent molecules 1a and 2a compare well with those calculated at the semiempirical PM3 level of theory. These results give credence to the PM3 calculated structures of 2,4,6,6-tetraazido-2,4-bis(piperidyl)cy-clotri(phosphazene) ( 1b ) and 2,4,6-triazido-2,4,6-tris(piperidyl)cyclotri(phosphazene) ( 2b ) for which presently there are no experimental data available.

1 Non-SI units employed: 1 kcal≈︁4.184 kJ, 1 Å = 10⁻¹⁰ m (since these units are still used in computational chemistry, we employed them throughout this article).

© 1997 John Wiley & Sons, Inc. Heteroatom Chem 8: 267–271, 1997.     

Cetylpyridinium Chloride as a Regulator in Paper Separation of 2,4‐Dichlorophenol and 2,4,6‐Trichlorophenol in Water

2,4‐Dichlorophenol (2,4‐DCP) and 2,4,6‐trichlorophenol (2,4,6‐TCP) by the use of cetylpyridinium chloride (CPCl) as a regulator was studied for their separation by the paper capillary permeation adsorption (PCPA) separation technique. The effect of pH, the type of PCPA treatment, the concentration of cetylpyridinium chloride, and various inorganic salts on the separatability has been investigated. A nearly 100% separatability was obtained at pH values 5–11 and 5–11, respectively, for 2,4‐dichlorophenol and 2,4,6‐trichlorophenol when cetylpyridinium chloride was present. It was confirmed that 2,4‐dichlorophenol and 2,4,6‐trichlorophenol are separated by adsorption on the fiber surface as ion pairs at the pH. Addition of inorganic salts decreases the separatability.     

Toxicity identification of gamma-ray treated phenol and chlorophenols

Ionizing radiation, such as gamma-rays and electron-beams, has been applied to modify toxicity of refractory pollutants and industrial wastewaters, however, very few studies reported the cause of toxicity changes by radiation treatment. In this work, degradation of phenol and chlorophenols (5·10⁻⁴M) by gamma-ray treatment and consequent toxicity changes were evaluated. Toxicity of 2,4-dichlorophenol (2,4-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP) was gradually decreased with increasing absorbed dose of gamma-radiation. However, in the case of phenol and monochlorophenols (2-, 3-, and 4-CPs), toxicity was dramatically increased particularly, for a dose of as low as 1 kGy. Hydroquinone, benzoquinone, catechol, chlorohydroquinone, and 4-chlorocatechol were identified to be main by-products of gamma-ray treatment. From the solid phase extraction (SPE) fractionation study, toxicity-causing by-products were found to be hydroquinone, benzoquinone, chlorohydroquinone, and/or 4-chlorocatechol.     

Photooxygenation of tetramethylallene competing (2+2) cycloaddition and ene-reactions with singlet oxygen

TPP-sensitized photooxygenation of tetramethylallene (4) in carbon tetrachloride yields acetone (5), 2,4-dimethyl-4-hydroxy-1-penten-3-one (8) and 2,4-dimethyl-1,4-pentadien-3-one (9) in a ratio of 35:20:45, besides minor amounts of resinous products and carbon dioxide. Isomerization of 4 to 2,4-dimethyl-1,3-pentadiene (6) does not occur under the reaction conditions. DABCO quenches the photooxygenation, whereas 2,4,6-tri-t-butylphenol (10) enhances the oxygen consumption rate but leaves the ratio of 5:8:9 unchanged. These results indicate that 4 is oxygenated by singlet oxygen. A mechanism is proposed according to which acetone is generated via a (2+2) cycloaddition whereas 8 and 9 are formed via an ene-reaction between 4 and singlet oxygen.     

Preparation and performance of plasticizers for poly(vinyl chloride) from products of thermal decomposition of waste polystyrene

2,4-Diphenylbutyl-2,4-diphenylbutyrate (DPBDPB) and 2,4,6-triphenylhexyl-2,4,6-triphenylhexoate (TPHTPH), plasticizers for poly(vinyl chloride), were synthesized from the products of thermal decomposition of waste polystyrene. Their heat stabilities were studied by thermogravimetric analysis and differential thermal analysis, and compared with those of typical plasticizers for PVC such as dibutyl phthalate (DBP), dihexyl phthalate (DHP) and bis(2-ethylhexyl) phthalate (DOP). DPBDPB and TPHTPH showed much higher heat resistance than DOP. PVC was plasticized with a mixed system consisting of DOP as the primary plasticizer and DPBDPB as the secondary. It became clear that DPBDPB is an excellent heat-resistant plasticizer which does not affect the compatibility of PVC with DOP.     

Styrylpyridine-based epoxy resins: Synthesis and characterization

Polymers containing rigid aromatic structures in the chain backbone usually gave high thermal stability and good flammability resistance. Three glycidyl ethers of epoxy resins were prepared from 2,4-di(p-hydroxystyryl)pyridine (2,4-DGESP), 2,6-di-(p-hydroxystyryl)pyridine (2,6-DGESP), and 2,4,6-tri-(p-hydroxystyryl)pryidine (2,4,6-TGESP) to study the relationships of structure to polymer degradation. To prepare a highly crosslinked material, trimethoxyboroxine (TMB) was used as the curing agent. The relative char yields of the three different resins, as measured by TGA, were 2,4-DGESP ≈ 2,6-DGESP > 2,4,6-TGESP. The char yield of the cured 2,6-DGESP varied with different amounts of the TMB curing agent, and was higher than the uncured 2,6-DGESP. The oxygen index increased as a function of thermal curing time for the 2,6-DGESP epoxy resin. An intermolecular Diels–Alder reaction with 2,6-DGESP is proposed as a primary reaction during thermal curing.