Thermal degradation of poly(alkyl acrylates). II. Primary esters: Ethyl,n-propyl,n-butyl,and 2-ethylhexyl

Quantitative analyses of the products of thermal degradation of poly(ethyl acrylate), poly(n-propyl acrylate), poly(n-butyl acrylate) and poly(2-ethylhexyl acrylate) have been made, principally by the combined application of GLC and mass and infrared spectroscopy. Data are recorded in mass balance tables. The major gaseous products are carbon dioxide and the olefin corresponding to the ester group. The minor gaseous products include the corresponding alkane, the alkane/olefin ratio being of the order of 10^?2–10^?3, and traces of carbon monoxide and hydrogen. The alcohol corresponding to the alkyl group is the major liquid product but there are also traces of monomer and the corresponding methacrylate. Alcohol production exhibits autocatalytic properties. The chain fragment fractions of the products are colored yellow and have average chain lengths of 3.2, 3.3, 3.6, and 5.6 for the ethyl, n-propyl, n-butyl and 2-ethylhexyl esters, respectively. The infrared spectra are similar to those of the parent polymers but with well defined differences. Insolubility develops in the ethyl, n-propyl, and n-butyl esters, but the residual material from poly(2-ethylhexyl acrylate) remains soluble even at very advanced stages of degradation. All of these products and reaction characteristics are accounted for in terms of radical reactions with a unique initiation step.     

Preparation and characterization of pavement materials with phase-change temperature modulation

A kind of pavement crack repairing material with temperature regulation property was successfully prepared through one-step method, in which the paraffin was incorporated into the polyurethane/epoxy resin-interpenetrating polymer networks. Differential scanning calorimeter results indicated that the phase-change latent heat of sample A was 14.4 kJ kg^?1, and the phase transition temperature was ??0.3 °C. FTIR and thermogravimetry measurements verified that the paraffin was successfully incorporated into the interpenetrating polymer network without leakage and reacted with the carrier, which exhibited high thermal stability above 300 °C. After 1 year of road test, there was no breakage for the repairing pavement with paraffin–polyurethane/epoxy resin-interpenetrating polymer networks, and there was almost no change for the accumulated attenuation of phase-change latent heat. Therefore, the materials of paraffin–polyurethane/epoxy resin-interpenetrating polymer networks have good chemical stability and thermal stability.

     

Nanocomposite phase change materials based on NaCl–CaCl2 and mesoporous silica

The synthesis of phase change materials based on NaCl–CaCl₂ molten salt mixture and mesoporous silica was investigated. The influence of mesoporous silica porosity and salt concentration on the thermal energy storage properties of the resulting materials is discussed. The nanocomposite samples were characterized by X-ray diffraction, differential scanning calorimetry, infrared spectroscopy, thermogravimetry, scanning electron microscopy and X-ray photoelectron spectroscopy. The mesoporous silica was found to act as a reactive matrix for the molten salts. Composite samples with up 95% wt. salt can be obtained and used as shape-stabilized phase change materials. The materials have heat of fusion values of up to 60.8 J g^?1 and specific heat capacity between 1.0 and 1.1 J g^?1 K^?1. The samples exhibit thermal stability up to 700 °C and can be used for high-temperature thermal energy storage through both latent and sensible heat storage mechanisms.

     

Cyclopentyl decanoate and butyl cyclopentanecarboxylate conversions into ketones over solid catalyst

Summary Cyclopentyl n-decanoate and n-butyl cyclopentanecarboxylate were converted into ketones over heterogeneous catalyst. The transformations proceeded as parallel ones: through b-ketoesters with simultaneous thermal decomposition (retro-Tishchenko reaction) and secondary condensation of the resultant aldehydes. The path from esters to ketones from acidic ester sides is shorter than the one from alcohol ester sides. The mutual proportions of ketones depend also on the control parameters.     

Kinetics and mechanism of oxidation of some aliphatic esters by sodium N-bromo-p-toluenesulfonamide

The kinetics of oxidation of methyl, ethyl, n-propyl, isopropyl, and n-butyl acetates to acetic acid and the corresponding aldehyde by the title oxidant in aqueous HCl medium at 40°C has been studied. The reaction shows first-order with respect to [oxidant] and fractional orders in [H⁺] and [ester]. An isokinetic relationship was observed with β = 374 K indicating enthalpy as the rate controlling factor. Attempts have been made to arrive at a linear free energy relationship through the Taft treatment. Electron releasing groups in the ester moiety increase the rate with ρ* = ?9.88. A two-pathway mechanism, consistent with the observed kinetic data, has been proposed. © 1993 John Wiley & Sons, Inc.     

The preparation of inorganic/organic hybrid nanomaterials containing silsesquioxane and its reinforcement for an epoxy resin network

A series of new inorganic/organic hybrid nanomaterials were prepared through the reaction of cage octa(γ-aminopropylsilsesquioxane) with n-butyl glycidyl ether. The structures and properties of these hybrid materials were characterized by Fourier transform infrared spectroscopy, ²⁹Si nuclear magnetic resonance (NMR), ¹H-NMR, and mass spectrometry spectra. The hybrid materials were used for improving mechanical and thermal properties of epoxy resin E-51. The results showed that appropriate amount of addition of the hybrids could enhance the fracture elongation ratio and impact strength. The tensile strength decreased with the addition of the hybrids. The thermal properties such as glass transition temperature, antioxidant index, decomposition temperature, and Vicat softening temperature were obviously improved. Scanning electron microscope observation displayed a rough structure inside the cured epoxy resin by the addition of the hybrids. Kinetic study indicated that the curing process was continuous with average activation energy of 48.06 kJ/mol which was based on Kissinger and Flynn–Wall–Ozawa models.     

Enantioseparation of Three β-Agonists Using Di-n-butyl d-Tartrate-Boric Acid Complex as Chiral Selector by Means of MEEKC

In this study, a self-prepared complex chiral selector, di-n-butyl d-tartrate-boric acid complex, by the reaction of di-n-butyl d-tartrate with boric acid in a running buffer was used as a chiral selector for the enantioseparation of three β-agonists including clenbuterol, cycloclenbuterol and tulobuterol by means of microemulsion electrokinetic chromatography (MEEKC). Three β-agonists were successfully enantioseparated using the chiral system, indicating that the di-n-butyl d-tartrate-boric acid complex was a useful chiral selector. The effects of di-n-butyl d-tartrate and sodium tetraborate concentration, surfactant concentration, cosurfactant, phosphate, buffer pH and composition, as well as applied voltage were extensively investigated to achieve a good enantioseparation. The di-n-butyl d-tartrate and sodium tetraborate concentration in the running buffer had great influence on the chiral resolution (R _s). Three β-agonists which could not be separated with only di-n-butyl d-tartrate, obtained good chiral separation using the complex chiral selector; among them, two pairs including clenbuterol and cycloclenbuterol could be baseline resolved in 7 min under optimized experimental conditions of 0.8% (w/v) di-n-butyl d-tartrate, 40 mM sodium tetraborate, 3.0% (w/v) Tween-20 and 60 mM sodium dihydrogen phosphate with 25 kV as running voltage. The results indicated that the method could be used for the enantioseparation of three β-agonists.

     

Preparation and characterization of form-stable tetradecanol–palmitic acid expanded perlite composites containing carbon fiber for thermal energy storage

In this study, tetradecanol–palmitic acid/expanded perlite composites containing carbon fiber (TD-PA/EP-CF CPCMs) were prepared by a vacuum impregnation method. Binary eutectic mixtures of PA and TD were utilized as thermal energy storage material in the composites, where EP behaved as supporting material. X-ray diffraction demonstrated that crystal structures of PA, TD, EP, and CF remained unchanged, confirming no chemical interactions among raw materials besides physical combinations. The microstructures indicated that TD-PA was sufficiently absorbed into EP porous structure, forming no leakage even in molten state. Differential scanning calorimetry estimated the melting temperature of TD-PA/EP-CF CPCM to 33.6 °C, with high phase change latent heat (PCLH) of 138.3 kJ kg⁻¹. Also, the freezing temperature was estimated at 29.7 °C, with PCLH of 137.5 kJ kg⁻¹. The thermal cycling measurements showed that PCM composite had adequate stability even after 200 melting/freezing cycles. Moreover, the thermal conductivity enhanced from 0.48 to 1.081 W m⁻¹ K⁻¹ in the presence of CF. Overall, the proposed CPCMs look promising materials for future applications due to their appropriate phase change temperature, elevated PCLH, and better thermal stability.

     

Measurement of reaction cross-sections for 64Ni(n, γ) 65Ni at E n = 0.025 eV and 58Ni(n, p) 58Co at E n = 3.7 MeV

The reaction cross-sections for ⁶⁴Ni(n, γ) ⁶⁵Ni at E _n  = 0.025 eV and ⁵⁸Ni (n, p) ⁵⁸Co at E _n  = 3.7 MeV have been experimentally determined using activation and off-line γ-ray spectrometric technique. The thermal neutron flux used is from the thermal Column of the reactor APSARA at BARC, Mumbai, whereas the neutron energy of 3.7 MeV is from the ⁷Li(p, n) reaction at Pelletron facility, TIFR, Mumbai. The ⁶⁴Ni(n, γ) ⁶⁵Ni and ⁵⁸Ni(n, p) ⁵⁸Co reactions cross-sections from present work are compared with the available literature data and found to be in good agreement. The ⁵⁸Ni(n, p) ⁵⁸Co reaction as a function of neutron energy is also calculated theoretically using TALYS computer code version 1.2 and found to be higher than the experimental data.     

Study on the thermal stability of 2-hexyne, 1-pentyne,ethyl isocyanide,and <Emphasis Type="Italic">n</Emphasis>-butyl isocyanide as sulfur-free gas odorants

In Japan, tert-butyl mercaptan (TBM) is mainly employed as an odorant of LPG. However, the sulfur component in TBM gives the adverse effect for environment and human body and/or has a negative impact on reforming catalyst of fuel cell and other types of cogeneration systems. In this way, the development of sulfur-free odorant is expected. This study focuses on the thermal stability and combustibility of 2-hexyne, 1-pentyne, n-butyl isocyanide (BIC), and ethyl isocyanide (EIC) that is expected as the candidate odorants. As the result of DSC measurement, the comparison of T _DSC indicated that 2-hexyne and 1-pentyne are more thermally stable than BIC and EIC. However, in 2-hexyne and 1-pentyne, the slight exothermic peaks were observed at lower temperature region before those main exothermic peaks. In 2-hexyne, copper or aluminum increased the heat amount of that slight exothermic peak observed before main peak. In 1-pentyne with zinc, T _DSC was approximately decreased to 279 °C from 337 °C of 1-pentyne alone. As the results of ARC measurement, in the presence of oxygen, the exothermic heat of 2-hexyne and 1-pentyne was observed at approximately 50–100 °C. This heat release may be corresponding to the slight heat release observed by DSC, and it thought to be results from the reaction with atmospheric oxygen. In this way, for the practical application of 2-hexyne and 1-pentyne as odorants, it is important to suppress the invasion of oxygen in the cylinder to low as much as possible in respect of the storage of the candidate odorant. As a result of thermal equilibrium calculation, even if either candidate odorant is added at about 100 ppm, there is little influence on propane combustibility from the adiabatic flame temperature, species of combustion gas and their yields.     

Studies on some radical transfer reactions by entrapping the radicals as polymer end groups. I. Reaction of hydroxyl radicals with amines

The reaction of OH radicals with a number of amines has been studied by entrapping the resultant radicals as polymer end groups which have been detected and estimated by the sensitive dye partition technique. Expressions have been developed relating the average amounts of end groups per polymer molecule to the rate constant of the radical transfer reaction, the rate constants determined for reaction with n-butyl, n-hexyl, and n-octyl amine being 1.00 × 10¹⁰, 1.31 × 10¹⁰, and 1.46 × 10¹⁰ mol^?1 L s^?1, respectively, at 25°C. The order of reactivity for amines of different classes has been found to be as primary < secondary > tertiary, the rate constants for reaction with n-butyl, dibutyl, and tributyl amine being 1.00 × 10¹⁰, 1.81 × 10¹⁰, and 1.67 × 10¹⁰ mol^?1 L s^?1, respectively, at 25°C. The change in the reactivity of the amine with chain length and amine class has been explained by activation and deactivation of the CH₂ group from which H abstraction by OH radicals occurs, respectively, by the alkyl group and by the protonated amino nitrogen under the acidic condition of the medium. Between pH 1.00 and 2.17, the rate of the reaction with n-butyl amine remains practically unchanged, but from pH 2.20 to 2.72 the rate constant increases with increasing pH, indicating that deprotonation of the positively charged nitrogen starts at about pH 2.20. The method is simple and accurate and can be applied to detect and estimate very reactive radicals.     

Pervaporation performance of crosslinked polydimethylsiloxane membranes for deep desulfurization of FCC gasoline: I. Effect of different sulfur species

Crosslinked PDMS/PEI composite membranes were prepared, in which asymmetric PEI membrane prepared with phase inversion method was acted as the microporous supporting layer in the flat-plate composite membrane. The different function composition of the PDMS/PEI composite membranes were characterized by reflection FTIR. The surface and section of PDMS/PEI composite membranes were investigated by scanning electron microscope (SEM). The infinite dilute activity and diffusion coefficients of thiophene, 2-methyl thiophene, 2,5-dimethyl thiophene, n-butyl mercaptan, n-butyl sulfide in crosslinked PDMS were measured in the temperature range of 80–100 °C by inverse gas chromatography. The solubility parameters of thiophene, 2-methyl thiophene, 2,5-dimethyl thiophene, n-butyl mercaptan, n-butyl sulfide were calculated by the group contribution method and the selectivity of PDMS composite membrane for different organic sulfur compounds was investigated. The composite membranes prepared in this work were employed in pervaporation separation of n-heptane and different sulfur forms mixtures. The theoretical results showed good agreement with the experimental results, and the order of partial permeate flux and selectivity for different organic sulfur compounds was: thiophene > 2-methylthiophene > 2,5-dimethylthiophene > n-butyl mercaptan > n-butyl sulfide, which should be significant for practical application.     

Synthesis of 2-Substituted and 2,3-Disubstituted Quinazolin-4-ones Containing a Sterically Hindered Phenol Residue

A series of 2-substituted and 2,3-disubstituted quinazolin-4-ones containing a 3,5-di(tert-butyl)-4-hydroxyphenyl group has been synthesized. They were prepared by the condensation of carboxylic acid imino ester hydrochlorides containing the indicated fragment with ethyl anthranilate and also by the reaction of azomethines, N-acylhydrazones, or the 4-phenylthiosemicarbazone of 3,5-di(tert-butyl)-4-hydroxybenzaldehyde with 2-methyl-4H-2,1-benzoxazin-4-one.     

Cationic polymerization of vinyl monomers initiated by 10-methylphenothiazine cation radicals

A small quantity of 10-methylphenothiazine cation radical (MPT^.+), electrochemically prepared and stocked in acetonitrile solution, initiated cationic polymerizations of n-butyl, t-butyl, and 2-methoxyethyl vinyl ethers and p-methoxystyrene, while no initiation occurred for phenyl vinyl ether, styrene, methyl methacrylate, and phenyl glycidyl ether. ¹H-NMR studies of oligomers and low molecular weight compounds isolated from the reaction mixture for the polymerization of t-butyl vinyl ether in the presence of a small amount of D₂O indicated that electron transfer from the monomer to MPT^.+ was involved in the initiation step. ¹H- and ¹³C-NMR and MO calculation implied that monomers with higher electron densities on the vinyl groups and with lower ionization potentials were more susceptible to the initiation of MPT^.+. © 1994 John Wiley & Sons, Inc.     

Synthesis and polymerization of vinyl esters and vinyl ethers having bulky substituents

In order to clarify the effect of bulky substituents on the stereoregulation of vinyl monomers, vinyl-1-adamantanecarboxylate and vinyl 1-adamantyl ether were synthesized and polymerized by radical and cationic mechanisms, respectively. As open-chain models of the adamantyl group, vinyl trialkylacetate (alkyl = ethyl, n-propyl, and n-butyl) and vinyl tri-n-propylcarbinyl ether were also synthesized and polymerized. The adamantly group in the vinyl ester favored syndiotactic propagation in a manner similar to the trimethylcarbinyl group. Higher homologs of tri-n-alkylcarbinyl group showed higher syndiotacticity but this effect was saturated in higher members of the series. The effect of the adamantyl group in vinyl ether was similar to that of the tert-butyl group, leading to high isotacticity on cationic polymerizations in nonpolar solvents and to atactic polymers in polar solvents, but the tri-n-propylcarbinyl group was found unique in leading to what was assumed to be a heterotactic polymer. Polymers with the adamantyl group showed much higher softening points than polymers of the corresponding open-chain groups.     

Thermal stability and lifetime of [AMIM]Cl-PFSA composite membranes

1-Allyl-3-methylimidazolium chloride [AMIM]Cl hybrid perfluorosulfonic acid (PFSA) composite electrolyte membrane was prepared and characterized by TG and FTIR technique. The conductivity was measured using AC impedance method. The results showed that when raised from 20 to 90 °C, the conductivity of composite membrane was increased from 4.50 × 10⁻⁶ to 1.34 × 10⁻⁵ S cm⁻¹, before and after the modification of triethylamine, the thermal stability of composite membrane was not changed, but the TEA-PFSA with [AMIM]Cl reactivity was a little difference. However, the heat resistance of composite membrane was significantly enhanced compared with that of PFSA membrane, the peak temperature of composite membrane almost disappeared in first stage, and offset to the high-temperature zone. When heated at 350 °C, the decomposition rate of PFSA, 10%[AMIM]Cl-PFSA and 10%[AMIM]Cl-TEA-PFSA membrane was 13.71, 3.67 and 1.26%, respectively. If the decomposition process follows isothermal first-order reaction and the conversion rate α is 10%, the activation energy E _α of the composite membrane is 97.4 kJ mol⁻¹. Besides, the isothermal lifetime of composite membrane was also measured.

     

Poly(alkyl α-bromoacrylate)s. III. Tacticity analysis from 19 mHz 13C-NMR spectroscopy

Polymer tacticity was determined by 19 mHz ¹³C-NMR spectroscopy for isotactic, atactic, and syndiotactic samples of six poly(alkyl α-bromoacrylate)s. Included in this series were the methyl, ethyl, n-propyl, i-propyl, n-butyl, and n-pentyl esters. Complete assignments for the 10 pentad peaks of the carbonyl carbon resonance were achieved for all but the i-propyl ester while a complete analysis of tetrad tacticity from the backbone methylene carbon resonance was possible for all but the methyl ester. The tetrad values calculated from the experimentally determined pentad contents were found to agree with the experimental tetrad values. As a result of insufficient peak separation of the quaternary carbon resonance, complete pentad assignments were possible in only a few instances. The polymerization reaction mechanisms were discussed in terms of the propagation statistics calculated from the experimentally determined tetrads and pentads. Both the atactic and syndiotactic polymers that were synthesized by free radical techniques displayed Bernoullian or random statistics while the stereochemical statistics of the isotactic polymers synthesized by a modified Grignard complex were more consistent with nonrandom or first-order Markovian statistics.     

Functionalization of substituted 2(1H)-pyridones. V. The synthesis of 1,2-dihydro-2-oxo-3,5-pyridinedicarboxylic acid derivatives through a novel dianion route

A new pyridone dianion was prepared by halogen-metal exchange from 5-bromo-1,2-dihydro-2-oxo-3-pyrid-inecarboxylic acid, t-butyl ester and two equivalents of n-butyllithium. This 1,5-dianion readily reacted at C₅ with electrophiles. Quenching with carbon dioxide gave the previously unreported 1,2-dihydro-2-oxo-3,5-pyridine dicarboxylic acid, 3-t-butyl ester. The 5-carboxyl groups were selectively converted to the ethyl ester and the ethyl amide through the 5-imidazolide. The 3-t-butyl ester was easily removed from all derivatives with acid hydrolysis.     

Aminolysis of n-butyl methacrylate–styrene copolymer with Di- and trifunctional amines

Aminolysis of a random copolymer of styrene and n-butyl methacrylate (2.54:1.00 mole ratio) with 6-aminohexanol has been studied. Kinetics were determined by covalently dyeing the functional polymer and spectrally measuring dye content. In the presence of 1,4-diaza[2,2,2]bicyclooctane (DABCO), an activation energy of 22.2 ± 1.0 kcal/mole was calculated from the temperature dependence of the overall rate of reaction. The rate is independent of solvent polarity. The rate at 189°C is 2.1-fold slower than that of poly(n-butyl methacrylate). The phenyl group of the styryl moiety inhibits the reaction, apparently via a steric effect. This aminolysis technique affords noncrosslinked (similar M?_n and M?_w) functional polymers. By a similar process an aminediol and an alcohol which contained a secondary and a primary amino group also yielded noncrosslinked functionalized polymers.     

In situ study of the interaction between <Emphasis Type="Italic">tert</Emphasis>-butyl chloride and aluminum activated with liquid In-Ga eutectic

The interaction between tert-butyl chloride and activated aluminum was studied by attenuated total reflectance Fourier transform infrared spectroscopy near room temperature (18–25°C). A long induction period of ∼240–260 min was observed. The ionic aluminum chloride complexes [Al _n Cl_3n+1]⁻ (n = 1, 2) and the molecular species AlCl₃ were identified at the activated aluminum/tert-butyl chloride interface during the reaction. The formation of the ion in the AlCl₄⁻ ion in the liquid medium and the presence of the same ion and a molecular AlCl₃-tert-butyl chloride complex in the resinous products of the reaction were confirmed by ²⁷Al NMR spectroscopy. The reaction products were analyzed qualitatively by GC/MS. The reactivities of activated aluminum and anhydrous aluminum chloride toward tert-butyl chloride under the same conditions were compared. A distinctive feature of the interaction activated aluminum and tert-butyl chloride is the dominant formation of the AlCl₄⁻ ion. By contrast, the interaction between aluminum chloride and tert-butyl chloride yields the polynuclear ion Al₂Cl₇⁻ and, likely, Al₃Cl₁₀⁻.