Photooxidative and pyrolytic degradation of methyl methacrylate-alkyl acrylate copolymers

Different compositions of poly(methyl methacrylate-co-methyl acrylate) (PMMAMA), poly(methyl methacrylate-co-ethyl acrylate) (PMMAEA) and poly(methyl methacrylate-co-butyl acrylate) (PMMABA) copolymers were synthesized and characterized. The photocatalytic oxidative degradation of all these copolymers were studied in presence of two different catalysts namely Degussa P-25 and combustion synthesized titania using azobis-iso-butyronitrile and benzoyl peroxide as oxidizers. Gel permeation hromatography (GPC) was used to determine the molecular weight distribution of the samples as a function of time. The GPC chromatogram indicated that the photocatalytic oxidative degradation of all these copolymers proceeds by both random and chain end scission.Continuous distribution kinetics was used to develop a model for photocatalytic oxidative degradation considering both random and specific end scission. The degradation rate coefficients were determined by fitting the experimental data with the model. The degradation rate coefficients of the copolymers decreased with increase in the percentage of alkyl acrylate in the copolymer. This indicates that the photocatalytic oxidative stability of the copolymers increased with increasing percentage of alkyl acrylate. From the degradation rate coefficients, it was observed that the photocatalytic oxidative stability follows the order PMMABA > PMMAEA > PMMAMA. The thermal degradation of the copolymers was studied by using thermogravimetric analysis (TGA). The normalized weight loss and differential fractional weight loss profiles indicated that the thermal stability of the copolymer increases with an increase in the percentage of alkyl acrylate and the thermal stability of poly(methyl methacrylate-co-alkyl acrylate)s follows the order PMMAMA > PMMAEA > PMMABA. The observed contrast in the order of photostability and thermal stability of the copolymers was attributed to different mechanisms involved for the scission of polymer chain and formation of different products in both the processes.

Ultrasonic degradation of poly(methyl methacrylate-co-alkyl acrylate) copolymers

The copolymers, poly(methyl methacrylate-co-methyl acrylate) (PMMAMA), poly(methyl methacrylate-co-ethyl acrylate) (PMMAEA) and poly(methyl methacrylate-co-butyl acrylate) (PMMABA), of different compositions were synthesized and characterized. The effect of alkyl acrylate content, alkyl group substituents and solvents on the ultrasonic degradation of these copolymers was studied. A model based on continuous distribution kinetics was used to study the kinetics of degradation. The rate coefficients were obtained by fitting the experimental data with the model. The linear dependence of the rate coefficients on the logarithm of the vapor pressure of the solvent indicated that vapor pressure is the crucial parameter that controls the degradation process. The rate of degradation increases with an increase in the alkyl acrylate content. At any particular copolymer composition, the rate of degradation follows the order: PMMAMA > PMMAEA > PMMABA. It was observed that the degradation rate coefficient varies linearly with the mole percentage of the alkyl acrylate in the copolymer.

Photocatalytic degradation of methyl methacrylate copolymers

The photolytic and photocatalytic degradation of the copolymers poly(methyl methacrylate-co-butyl methacrylate) (MMA–BMA), poly(methyl methacrylate-co-ethyl acrylate) (MMA–EA) and poly(methyl methacrylate-co-methacrylic acid) (MMA–MAA) have been carried out in solution in the presence of solution combustion synthesized TiO2 (CS TiO2) and commercial Degussa P-25 TiO2 (DP 25). The degradation rates of the copolymers were compared with the respective homopolymers. The copolymers and the homopolymers degraded randomly along the chain. The degradation rate was determined using continuous distribution kinetics. For all the polymers, CS TiO2 exhibited superior photo-activity compared to the uncatalysed and DP 25 systems, owing to its high surface hydroxyl content and high specific surface area. The time evolution of the hydroxyl and hydroperoxide stretching vibration in the Fourier transform-infrared (FT-IR) spectra of the copolymers indicated that the degradation rate follows the order MMA–MAA > MMA–EA > MMA–BMA. The same order is observed for the rate coefficients of photocatalytic degradation. The photodegradation rate coefficients were compared with the activation energy of pyrolytic degradation. In degradation by pyrolysis, it was observed that MMA–BMA was the least stable followed by MMA–EA and MMA–MAA. The observed contrast in the order of thermal stability compared to the photo-stability of these copolymers was attributed to the two different mechanisms governing the scission of the polymer and the evolution of the products.

Utilizing an ionic liquid for synthesizing a soft matter polymer ``gel'' electrolyte for high rate capability lithium-ion batteries

A cross-linked polymer ``gel'' electrolyte obtained from free radical polymerization of a vinyl monomer (acrylonitrile; AN) in a room temperature ionic liquid electrolyte (N,N-methyl butyl pyrrolidinium-bis (trifluoromethanesulphonyl)imide-lithium bis(trifluoromethanesulphonyl) imide;LiTFSI-[Py(1,4)-TFSI]) for application in high rate capability rechargeable lithium-ion batteries is discussed here. This is a novel alternative compared to the often employed approach of using a molecular liquid as the medium for performing the polymerization reaction. The polymer ``gel'' electrolytes (AN:Py(1,4)-TFSI = 0.16-0.18, w/w) showed remarkable compliable mechanical strength and higher thermal stability compared to LiTFSI-[Py(1,4)-TFSI]. Despite two orders increase in magnitude of viscosity of polymer ``gels'', the room temperature ionic conductivity of the ``gels'' (1.1 x 10(-3)-1.7 x 10(-3) Omega(-1) cm(-1)) were nearly identical to that of the ionic liquid (1.8 x 10(-3) Omega(-1) cm(-1)). The present ``gel'' electrolytes did not exhibit any ageing effects on ionic conductivity similar to the conventional polymer gel electrolytes (e.g. high molecular weight polymer + salt + high dielectric constant molecular solvent). The disorder (ionic liquid) to a relative order (cross-linked polymer electrolyte) transformation does not at all influence the concentration of conducting species. The polymer framework is still able to provide efficient pathways for fast ion transport. Unlike the ionic liquid which is impossible to assemble without a conventional separator in a cell, the polymer ``gel'' electrolyte could be conveniently assembled without a separator in a Li vertical bar lithium iron phosphate (LiFePO(4)) cell. Compared to the ionic liquid, the ``gel'' electrolyte showed exceptional cyclability and rate capability (current density: 35-760 mA g(-1) with LiFePO(4) electronically wired with carbon (amorphous or multiwalled nanotube [MWCNT]).

Thermal and Sonochemical Degradation Kinetics of Poly(n-butyl methacrylate-co-alkyl acrylates): Variation of Chain Strength and Stability with Copolymer Composition

The thermal degradation of poly(n-butyl methacrylate-co-alkyl acrylate) was compared with ultrasonic degradation. For this purpose, different compositions of poly (n-butyl methacrylate-co-methyl acrylate) (PBMAMA) and a particular composition of poly(n-butyl methacrylate-co-ethyl acrylate) (PBMAEA) and poly(n-butyl methacrylate-co-butyl acrylate) (PBMABA) were synthesized and characterized. The thermal degradation of polymers shows that the poly(alkyl acrylates) degrade in a single stage by random chain scission and poly(n-butyl methacrylate) degrades in two stages. The number of stages of thermal degradation of copolymers was same as the majority component of the copolymer. The activation energy corresponding to random chain scission increased and then decreased with an increase of n-butyl methacrylate fraction in copolymer. The effect of methyl acrylate content, alkyl acrylate substituent, and solvents on the ultrasonic degradation of these copolymers was investigated. A continuous distribution kinetics model was used to determine the degradation rate coefficients. The degradation rate coefficient of PBMAMA varied nonlinearly with n-butyl methacrylate content. The degradation of poly (n-butyl methacrylate-co-alkyl acrylate) followed the order: PBMAMA < PBMAEA < PBMABA. The variation in the degradation rate constant with composition of the copolymer was discussed in relation to the competing effects of the stretching of the polymer in solution and the electron displacement in the main chain. (C) 2012 Society of Plastics Engineers

1-butyl-3-methylimidazolium 3,5-dinitro-1,2,4-triazolate: a novel ionic liquid containing a rigid, planar energetic anion

The novel ionic liquid, 1-butyl-3-methylimidazolium 3,5-dinitro-1,2,4-triazolate has been synthesized and exhibits an unexpectedly low melting point (35 degreesC) considering the size and shape of the rigid, planar anion; analogous tetraalkylammonium salts (methyl, ethyl and n-butyl) have also been prepared and the tetraethylammonium example was characterized by single crystal X-ray diffraction.

Application of ionic liquids as plasticizers for poly(methyl methacrylate)

The room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate, [C(4)mim][PF6] was found to be an efficient plasticizer for poly( methyl methacrylate), prepared by in situ radical polymerization in the ionic liquid medium; the polymers have physical characteristics comparable with those containing traditional plasticizers and retain greater thermal stability.

Efficient, halide free synthesis of new, low cost ionic liquids: 1,3-dialkylimidazolium salts containing methyl- and ethyl-sulfate anions

New low-cost ionic liquids containing methyl- and ethyl-sulfate anions can be easily and efficiently prepared under ambient conditions by the reaction of 1-alkylimidazoles with dimethyl sulfate and diethyl sulfate. The preparation and characterization of a series of 1,3-dialkylimidazolium alkyl sulfate and 1,2,3-trialkylimidazolium alkyl sulfate salts are reported. 1,3-Dialkylimidazolium salts containing at least one non-methyl N-alkyl substituent are liquids at, or below room, temperature. Three salts were crystalline at room temperature, the single crystal X-ray structure of 1,3-dimethylimidazolium methyl sulfate was determined and shows the formation of discrete ribbons comprising of two anion-cation hydrogen-bonded chains linked via intra-chain hydrogen-bonding, but little, or no inter-ribbon hydrogen-bonding. The salts are stable, water soluble, inherently 'chloride-free', display an electrochemical window of greater than 4 V, and can be used as alternatives to the corresponding halide salts in metathesis reactions to prepare other ionic liquids including 1-butyl-3-methylimidazolium hexafluorophosphate.

Nitrile-Functionalized Pyridinium, Pyrrolidinium, and Piperidinium Ionic Liquids

Two series of 1-alkylpyridinium and N-alkyl-N-methylpiperidinium ionic liquids fiinctionalized with a nitrile group at the end of the alkyl chain have been synthesized. Structural modifications include a change of the alkyl spacer length between the nitrile group and the heterocycle of the cationic core, as well as adding methyl or ethyl substituents on different positions of the pyridinium ring. The anions are the bromide and the bis(trifluoromethylsulfonyl)imide ion. All the bis(trifluoromethylsulfonyl)imide salts as well as the bromide salts with a long alkyl spacer were obtained as viscous liquids at room temperature, but some turned out to be supercooled liquids. In addition, pyrrolidinium and piperidinium ionic liquids with two nitrile functions attached to the heterocyclic core have been prepared. The crystal structures of seven pyridinium bis(trifluoromethylsulfonyl)imide salts are reported. Quantum chemical calculations have been performed on model cations and ion pairs with the bis(trifluoromethylsulfonyl)imide anion. A continuum model has been used to take solvation effects into account. These calculations show that the natural partial charge on the nitrogen atom of the nitrile group becomes more negative when the length of the alkyl spacer between the nitrile functional group and the heterocyclic core of the cation is increased. Methyl or methoxy substituents on the pyridinium ring slightly increase the negative charge on the nitrile nitrogen atom due to their electron-donating abilities. The position of the substituent (ortho, meta, or para) has only a very minor effect on the charge of the nitrogen atom. The N-15 NMR spectra of the bis(trifluoromethylsulfonyl)imide ionic liquids were recorded with the nitrogen-15 nucleus at its natural abundance. The chemical shift of the N-15 nucleus of the nitrile nitrogen atom could be correlated with the calculated negative partial charge on the nitrogen atom.

A study of the thermal decomposition of allyl t-butyl peroxide and 3-hydroperoxy-1-propene (allyl hydroperoxide) in toluene /|nby Krishnankutty Nair V. G. -- 260 St. Catharines [Ont. : s. n.],

Kinetics and product studies of the decompositions of allyl-t-butyl peroxide and 3-hydroperoxy- l-propene (allyl hydroperoxide ) in tolune were investigated. Decompositions of allyl-t-butyl peroxide in toluene at 130-1600 followed first order kinetics with an activation energy of 32.8 K.cals/mol and a log A factor of 13.65. The rates of decomposition were lowered in presence of the radical trap~methyl styrene. By the radical trap method, the induced decomposition at 1300 is shown to be 12.5%. From the yield of 4-phenyl-l,2- epoxy butane the major path of induced decomposition is shown to be via an addition mechanism. On the other hand, di-t-butYl peroxyoxalate induced decomposition of this peroxide at 600 proceeded by an abstraction mechanism. Induced decomposition of peroxides and hydroperoxides containing the allyl system is proposed to occur mainly through an addition mechanism at these higher temperatures. Allyl hydroperoxide in toluene at 165-1850 decomposes following 3/2 order kinetics with an Ea of 30.2 K.cals per mole and log A of 10.6. Enormous production of radicals through chain branching may explain these relatively low values of E and log A. The complexity of the reaction is indicated a by the formation of various products of the decomposition. A study of the radical attack of the hydro peroxide at lower temperatures is suggested as a further work to throw more light on the nature of decomposition of this hydroperoxide.

Effects of sample solvent composition and injection volume on chromatographic peak profiles of methyl w- benzimidazolecarbamate and 3-butyl1-2,4-dioxo[1,2-a]-s- triazinobenzimidazole in RP-HPLC

The effects of sample solvent composition and the injection volume, on the chromatographic peak profiles of two carbamate derivatives, methyl 2-benzimidazolecarbamate (MBC) and 3-butyl-2,4-dioxo[1,2-a]-s-triazinobenzimidazole (STB), were studied using reverse phase high performance liquid chromatograph. The study examined the effects of acetonitrile percentage in the sample solvent from 5 to 50%, effects of methanol percentage from 5 to 50%, effects of pH increase from 4.42 to 9.10, and effect of increasing buffer concentration from ° to 0.12M. The effects were studied at constant and increasing injection mass and at four injection volumes of 10, 50, 100 and 200 uL. The study demonstrated that the amount and the type of the organic solvents, the pH, and the buffer strength of the sample solution can have a pronounced effect on the peak heights, peak widths, and retention times of compounds analysed. MBC, which is capable of intramolecular hydrogen bonding and has no tendency to ionize, showed a predictable increase .in band broadening and a decrease in retention times at higher eluting strengths of the sample solvent. STB, which has a tendency to ionize or to strongly interact with the sample solvent, was influenced in various ways by the changes in ths sample solvent composition. The sample solvent effects became more pronounced as the injection volume increased and as the percentage of organic solvent in the sample solution became greater. The peak height increases for STB at increasing buffer concentrations became much more pronounced at higher analyte concentrations. It was shown that the widely accepted procedure of dissolving samples in the mobile phase does not yield the most efficient chromatograms. For that reason samples should be dissolved in the solutions with higher aqueous content than that of the mobile phase whenever possible. The results strongly recommend that all the samples and standards, regardless whether the standards are external or internal, be analysed at a constant sample composition and a constant injection volume.

The kinetics and mechanism of the thermal decomposition of bis diphenyl methyl and related peroxides in liquid phase /|nby C. Thankachan. -- 260 St. Catharines, Ont. : [s. n.],

Rates and products have been determined for the thermal decomposition of bis diphenyl methyl peroxide and diphenyl methyl tert* butyl peroxide at 110@~145@C* The decomposition was uniformly unimolecular with activation energies for the bis diphenyl methyl peroxide in tetrachloroethylene* toluene and nitrobenzene 26,6* 28*3f and 27 Kcals/mole respectively. Diphenyl methyl tert* butyl peroxide showed an activation energy of 38*6 Kcals/mole* About 80-90% of the products in the case of diphenyl methyl peroxide could be explained by the concerted process, this coupled with the negative entropies of activation obtained is a conclusive evidence for the reaction adopting a major concerted path* All the products in the case of diphenyl methyl peroxide could be explained by known reactions of alkoxy radicals* About 80-85% of tert butanol and benzophenone formed suggested far greater cage disproportionation than diffusing apart* Rates of bis triphenyl methyl peroxide have been determined in tetrachloroethylene at 100-120@C* The activation energy was found to be 31 Kcals/mole*

Asymmetric synthesis of (1R,2S,3R)-3-methylcispentacin and (1S,2S,3R)-3-methyltranspentacin by kinetic resolution of tert-butyl (+/-)-3-methylcyclopentene-1-carboxylate

Conjugate addition of lithium dibenzylamide to tert-butyl (+/-)-3-methylcyclopentene-1-carboxylate occurs with high levels of stereocontrol, with preferential addition of lithium dibenzylamide to the face of the cyclic alpha,beta-unsaturated acceptor anti- to the 3-methyl substituent. High levels of enantiorecognition are observed between tert-butyl (+/-)-3-methylcyclopentene-1-carboxylate and an excess of lithium (+/-)-N-benzyl-N-alpha-methylbenzylamide (10 eq.) (E > 140) in their mutual kinetic resolution, while the kinetic resolution of tert-butyl (+/-)-3-methylcyclopentene-1-carboxylate with lithium (S)-N-benzyl-N-alpha-methylbenzylamide proceeds to give, at 51% conversion, tert-butyl (1R, 2S, 3R,alphaS)-3-methyl-2-N-benzyl-N-alpha-methylbenzylaminocyclopentane-1-c arboxylate consistent with E > 130, and in 39% yield and 99 +/- 0.5% de after purification. Subsequent deprotection by hydrogenolysis and ester hydrolysis gives (1R, 2S, 3R)-3-methylcispentacin in > 98% de and 98 +/- 1% ee. Selective epimerisation of tert-butyl (1R, 2S, 3R, alphaS)-3-methyl-2-N- benzyl-N-alpha-methylbenzylaminocyclopentane-1-carboxylate by treatment with (KOBu)-Bu-t in (BuOH)-Bu-t gives tert-butyl (1S, 2S, 3R, alphaS)-3-methyl-2-N-benzyl-N-alpha-methylbenzylaminocyclopentane-1-carb oxylate in quantitative yield and in > 98% de, with subsequent deprotection by hydrogenolysis and ester hydrolysis giving (1S, 2S, 3R)-3-methyltranspentacin hydrochloride in > 98% de and 97 +/- 1% ee.

Synthesis, crystal structures and magnetic properties of a phenoxo-bridged dinuclear Cu(II) complex and a dicyanamide bridged novel molecular rectangle based on it

The phenoxo-bridged dinuclear Cu-II complex [Cu2L2-(NCNCN)(2)] (1) and the dicyanamide-bridged molecular rectangle [Cu4L4{mu(1,5)-(NCNCN)(2)}]center dot(ClO4)(2)(H2O)(2) (2) were synthesized using the tridentate reduced Schiff-base ligand HL {2-[(2-dimethylamino-ethylamino) methyl] phenol}. The complexes were characterized by X-ray structural analyses and variable-temperature magnetic susceptibility measurements. Complex 2 was formed through the joining of the phenoxo-bridged dinuclear Cu2O2 cores of 1 via the mu(1,5)-bridging mode of dicyanamide. The structural properties of the Cu2O2 cores in two complexes are significantly different. The geometry of the copper ions is distorted trigonal bipyramid in 1 but is nearly square-pyramidal in 2. These differences have a marked effect on the magnetic properties of two compounds. Although both are antiferromagnetically coupled, the coupling constants (J = -185.2 and -500.9 cm(-1) for 1 and 2, respectively) differ considerably.

A MORTALITY STUDY OF BUTYL-CHLOROBUTYL RUBBER WORKERS

Worker populations are potentially exposed to multiple chemical substances simultaneously during the performance of routine tasks. The acute health effects from exposure to toxic concentrations of these substances are usually well-described. However, very little is known about the long-term health effects of chronic low dose exposure to all except a few chemical substances. A mortality study was performed on a population of workers employed at a butyl rubber manufacturing plant in Baton Rouge, Louisiana for the period 1943-1978, with special emphasis on potential exposure to methyl chloride.^ The study population was enumerated using company records. The mortality experience among the population was evaluated by comparing the number of observed deaths (total and cause-specific) to the expected number of deaths, based on the U.S. general age, race, sex specific rates. An internal comparison population was assembled to address the issue of lack of comparability when the U.S. rates are used to calculate expected deaths in an employed population.^ There were 18% fewer total observed deaths compared to the expected when the U.S. death rates were used to obtain the expected. Deaths from specific causes were also less than expected except when numbers of observed and expected deaths were small. Similar results were obtained when the population was characterized by intensity and duration of potential exposure to methyl chloride. When the internal comparison population was utilized to evaluate overall mortality of the study population, the relative risk was about 1.2.^ The study results were discussed and conclusions drawn in light of certain limitations of the methodology and study population size. ^