A kinetic study of liquid-phase catalytic oxidation of styrene to benzaldehyde with Wilkinson complex

Liquid-phase homogeneous catalytic oxidation of styrene with Wilkinson complex by molecular oxygen in toluene medium gave selectively benzaldehyde and formaldehyde as the primary products. Higher temperatures and styrene conversions eventually led to acid formation due to co-oxidation of aldehyde.A reaction induction period and an initiation period, typical of free-radical reactions, characterized the oxidation process. The effects of temperature and catalyst and styrene concentrations on the conversion of styrene to benzaldehyde and acid formation have been studied. The optimum reaction parameters have been determined as a styrene-to-solvent mole ratio of 0.5, a catalyst-to-styrene mole ratio of 5.0 X lo4, and a reaction temperature of 75 "C. A reaction scheme based upon free-radical mechanism yielded a pseudo-first-order model which agreed well with the observed kinetic data in the absence of co-oxidation of aldehyde. A second-order model was found to fit the experimental data better in the case of aldehyde conversion to acid.

A low-cost lead-acid battery with high specific-energy

Lightweight grids for lead-acid battery grids have been prepared from acrylonitrile. butadiene styrene (ABS) copolymer followed by coating with lead. Subsequently, the grids have been electrochemically coated with a conductive and corrosion-resistant layer of polyaniline. These grids are about 75% lighter than those employed in conventional lead-acid batteries. Commercial-grade 6V/3.5 Ah (C-20-rate) lead-acid batteries have been assembled and characterized employing positive and negative plates constituting these grids. The specific energy of such a lead-acid battery is about 50 Wh/kg. The batteries can withstand fast charge-discharge duty cycles.

Super-plasticized natural rubber latex modified concretes

Polymeric admixtures to concrete ingredients modify the properties of the processed concrete. Ductility is one such property modification. This investigation deals with the development of a method of incorporating natural rubber latex into concrete ingredients with only marginal effects on the compressive strength of base plain concrete. This retention of the strength has been effected by reducing the water/cement ratio with the aid of a superplasticizer. The quantity of natural rubber latex is expressed as the dry rubber content by percentage of volume of concrete. The compressive and tensile strengths, as well as post peak ductile behaviour have been the basis for comparison with those of unmodified concrete.

Corona Aging Studies on Silicone Rubber Nanocomposites

In EHV and UHV power transmission lines, corona could occur even on well designed transmission line hardware and insulators especially under wet conditions. Corona if allowed to occur continuously can significantly damage the polymeric insulators used in such lines in the long run. This paper presents the experimental results of corona aging studies conducted on unfilled silicone rubber as well as filled silicone rubber nanocomposites. Corona aging studies were conducted on silicone rubber samples with filler concentrations of 0, 1, 2 and 3 % by wt of nanosilica for 25 h and 50 h. Needle-plane electrode geometry has been used to create the corona on the samples. Different characterization techniques such as Scanning Electron Microscopy, Energy Dispersive X-ray analysis, Hydrophobicity, Fourier Transform Infrared Spectroscopy, and Optical Profilometry have been used to assess the relative performance of the samples with respect to corona aging. Results indicate that at 3 wt %, the performance of the nanocomposite is much better than the unfilled silicon rubber which can be attributed to the modifications in the material caused by the size factor of the filler.

Miscibility of poly(phenyl acrylate) with acrylonitrile/styrene copolymers

The Blase transition and phase behavior of blends of poly(pheny1 acrylate) with poly(acrylonitri1eco-styrene) was studied by differential scanning calorimetry. It was found that poly(pheny1 acrylate) is miscible with poly(acrylonitri1e-co-styrenes) within a specific range of copolymer composition. The segmental interaction parameters were estimated and found to be positive for all three pairs. The miscibility in thissystem appears to be the consequence of the intramolecular repulsion between styrene and acrylonitrile units.

Oxidative copolymerization: microstructure analysis of the terpolymer of styrene, methyl methacrylate, and oxygen

This paper reports the first study of the microstructure of a copolyperoxide by nuclear magnetic resonance spectroscopy. The copolyperoxides of styrene and methyl methacrylate (MMA) of various compositions have been synthesized. An analysis of the resonance signal of the backbone methylene protons gave the diad sequence probabilities which led to the calculation of the oxidative copolymerization reactivity ratios for styrene and MMA and the microstructural parameters like average chain length of the repeat unit sequences, run number, etc. The results point to the tendency of the SO1 and MO:! units to alternate in the chain. Compared to poly(styrene peroxide), the aromatic C1 seems to be stereosensitive in the terpolymers.

Miscibility of Poly(aromatic acrylate)s and Methacrylates with Styrene/Acrylonitrile copolymers

Miscibilities of some poly[aromatic (meth)acrylatels namely, poly(pheny1 acrylate) (PPA), poly(pheny1 methacrylate) (PPMA), poly(benzy1 acrylate) (PBA), and poly(benzy1 methacrylate) (PBMAY polystyrene blends, have been studied through the so-called copolymer effect by incorporating acrylonitrile units in PS chains. In these systems, miscibility occurs on account of the strong repulsion between the acrylonitrile and styrene units in the copolymer. PBA and PBMA were blended with different styreneacrylonitrile (SAN) copolymers. A miscibility window has been identified for the latter system, and from these limits, the binary interaction energy density parameters (B,j.’sw) ere calculated. Using these values, the miscibilities in other homopolymer-copolymer and copolymer-copolymer systems containing benzyl methacrylate, acrylonitrile, and styrene monomer units have been predicted and subsequently verified experimentally. The miscibility window limits in poly[aromatic (meth)acrylate]s/SAN copolymer blends have been compared. PBA does not exhibit a miscibility window with SAN copolymers, which has been explained by the weak intramolecular hydrogen bonding in PBA. The miscibility window in the PBW SAN copolymer system, as observed by DSC, shows a considerable narrowing in nonradiative energy transfer (NRET) measurements, as this technique is more sensitive.

Miscibility of poly(aromatic acrylate)s and methacrylates with styrene/acrylonitrile copolymers

Miscibilities of some poly[aromatic (meth)crylate]s namely, poly(phenyl acrylate) (PPA, poly(phenyl methacrylate) (PPMA), poly(benzyl acrylate) (PBA), and poly(benzyl methacrylate) (PBMA)/polystyrene blends, have been studied through the so-called copolymer effect by incorporating acrylonitrile units in PS chains. In these systems, miscibility occurs on account of the strong repulsion between the acrylonitrile and styrene units in the copolymer. PBA and PBMA were blended with different styrene-acrylonitrile (SAN) copolymers. A miscibility window has been identified for the latter system, and from these limits, the binary interaction energy density parameters (Bij's) were calculated. Using these values, the miscibilities in other homopolymer-copolymer and copolymer-copolymer systems containing benzyl methacrylate, acrylonitrile, and styrene monomer units have been predicted and subsequently verified experimentally. The miscibility window limits in poly[aromatic (meth)acrylate]s/SAN copolymer blends have been compared. PBA does not exhibit a miscibility window with SAN copolymers, which has been explained by the weak intramolecular hydrogen bonding in PBA. The miscibility window in the PBMA/SAN copolymer system, as observed by DSC, shows a considerable narrowing in nonradiative energy transfer (NRET) measurements, as this technique is more sensitive.

Long-term Accelerated Weathering of Outdoor Silicone Rubber Insulators

Multistress aging/weathering of outdoor composite polymeric insulators has been a topic of interest for power transmission research community in the last few decades. This paper deals with the long-term accelerated weathering of full-scale distribution class silicone rubber composite insulators. To evaluate the long-term synergistic effect of electric stress, temperature and UV radiation on insulators, they were subjected to accelerated weathering in a specially designed multistress-aging chamber for 30,000 h. All the insulators were subjected to the same level of electrical and thermal stresses but different UV radiation levels. Chemical, physical and electrical changes due to degradation have been assessed using various techniques. It was found that there was a monotonous reduction of the content of low molecular weight (LMW) molecules with the duration of the weathering. Further, due to oxidation and weathering there is an appreciable increase in surface roughness and atomic percentage of oxygen. There is no change in the leakage current of new and aged insulators under both wet and dry conditions at the end of the aging. The results also indicate that there is no influence of UV radiation on the silicone rubber for the durations and conditions under which the studies were made.

A novel (main chain) (side chain) polymeric peroxide: Synthesis and initiating characteristics of poly(alpha-(tert-butylperoxymethyl)styrene peroxide)

A novel (main chain)-(side chain) vinyl polyperoxide, poly(alpha-(tert-butylperoxymethyl)styrene peroxide) (MCSCPP), an alternating copolymer of alpha-(tert-butylperoxymethyl)styrene (TPMS) and oxygen, has been synthesized by the oxidative polymerization of TPMS. The MCSCPP was characterized by H-1 NMR, C-13 NMR, IR, DSC, EI-MS, and GC-MS studies. The overall activation energy (E(a)) for the degradation of MCSCPP was found to be 27 kcal/mol. Formaldehyde and alpha-(tert-butylperoxy)acetophenone (TPAP) were identified as the primary degradation products of MCSCPP; TPAP was found to undergo further degradation. The side chain peroxy groups were found to be thermally more stable than those in the main chain. Polymerization of styrene in the presence of MCSCPP as initiator, at 80 degrees C, follows classical kinetics. The presence of peroxy segments in the polystyrene chain was confirmed by both H-1 NMR and thermal decomposition studies. Interestingly, unlike other vinyl polyperoxides, the MCSCPP initiator shows an increase in molecular weight with conversion.

Chemical Degradation of Poly(styrene disulfide) and Poly(styrene tetrasulfide) by Triphenylphosphine

The chemical degradation of polysulfide polymers, viz., poly(styrene disulfide), PSD, and poly(styrene tetrasulfide), PST, has been achieved using triphenylphosphine, TPP. The reaction was monitored using P-31 NMR spectroscopy. The solubility analysis of the reaction residues reveals that while PSD degrades completely, PST on the other hand, undergoes complete degradation only when the concentration of TPP is increased. Moreover, the reaction of PST with TPP occurs at room temperature whereas PSD requires a higher temperature. The reaction products were analyzed using the direct pyrolysis mass spectrometric (DP-MS) technique, and their formation has been explained through an ionic mechanism.

Microstructure of copolyperoxides of alpha-methylstyrene with styrene and methyl methacrylate

This paper reports a study on the microstructure of two series of copolyperoxides of alpha-methylstyrene, with styrene and with methylmethacrylate. The copolyperoxides were synthesized by the free radical-initiated oxidative copolymerization of the vinyl monomer pairs. The copolyperoxide compositions obtained from the H-1 and C-13 NMR spectra led to the determination of the reactivity ratios. The product of the reactivity ratios indicates that alpha-methylstyrene forms a block copolyperoxide with styrene and a random copolyperoxide with methylmethacrylate. Microstructural parameters like average sequence length, run number, etc. have been determined for the latter copolyperoxide from analysis of its C-13 NMR spectrum. The aromatic quaternary and carbonyl carbons were found to be sensitive to triad sequences. The end groups of the copolyperoxides have been identified by H-1 NMR as well as FTIR spectroscopic techniques. The thermal degradation of the copolyperoxides has been studied by differential scanning calorimetry, which confirms the alternating peroxide units in the copolyperoxide chain.

Synthesis and characterization of tetrapolymers of styrene, methyl methacrylate, alpha-methylstyrene, and oxygen

This paper presents the first report on a terpolyperoxide (TPPE) synthesized by the oxidative terpolymerization of styrene, methyl methacrylate, and a-methylstyrene. TPPEs of different compositions were synthesized by varying the vinyl monomers feed, and they were then characterized by spectroscopic and thermal studies. The conventional terpolymer equation has been used to predict the composition of TPPEs. The H-1 NMR chemical shift values of TPPEs were found to vary with the composition. The shape of the backbone methylene protons (4.00-4.50 ppm) was found to be sensitive to the sequence distribution of vinyl monomers in the polymer chain. Formaldehyde, benzaldehyde, acetophenone, and methyl pyruvate were identified as the primary degradation products. The overall thermal stability and the average enthalpy of degradation (Delta H-d), as obtained by thermogravimetric analysis and differential scanning calorimetry, respectively, do not vary much with the composition of TPPEs.

Synthesis of epoxy-terminated polymers by radical polymerization using alpha-(t-butylperoxymethyl)styrene as chain transfer agent

Epoxy-terminated polystyrene has been synthesized by radical polymerization using alpha-(t-butylperoxymethyl) styrene (TPMS) as the chain transfer agent. The chain transfer constants were found to be 0.66 and 0.80 at 60 and 70 degrees C, respectively. The presence of epoxy end groups was confirmed by functional group modification of epoxide to aldehyde by treatment with BF3.Et(2)O. Thermal stability of TPMS was followed by differential scanning calorimetry and iodimetry. Thermal decomposition of TPMS in toluene follows first order kinetics with an activation energy of 23 kcal/mol. (C) 1996 John Wiley & Sons, Inc.