Thermal Oxidation Of Poly Research Articles

Thermal oxidation of poly(dicyclopentadiene) - Effect of phenolic and hindered amine stabilizers

The thermal oxidation of stabilized polydicyclopentadiene was deeply studied here for the first time. Three kinds of antioxidants (phenolic antioxidant BHT, monomeric hindered amine in alkoxylated form Tinuvin 123 and oligomeric hindered amine Chimassorb 2020) were compared at the same concentrations. Tinuvin 123 was observed to me more efficient than Chimassorb 2020 because of the “activated” nature of alkoxyamine in Tinuvin 123. Results were simulated using a completed version of previously established kinetic model for thin PDCPD films in order to be able to make reliable lifetime prediction of stabilized PDCDP.

Oxidative polymerization of diphenylamine-2-carboxylic acid: Synthesis, structure, and properties of polymers

Polymers of diphenylamine-2-carboxylic acid are synthesized for the first time via chemical oxidative polymerization. The effects of the concentration of reagents, their ratio, and the temperature and time of reaction on the yield and chemical structure of poly(diphenylamine-2-carboxylic acid) are studied by IR and UV spectroscopy. It is shown that the growth of polymer chains proceeds through the C-C addition in the para position of phenyl rings relative to nitrogen. During the thermal oxidation of poly(diphenylamine-2-carboxylic acid), COOH groups and dopant molecules are successively eliminated; with a further increase in temperature, the polymer behaves as polydiphenylamine. The main processes of thermooxidative degradation of poly(diphenylamine-2-carboxylic acid) begin at 570°C. This value is 120°C higher than the corresponding parameter in the case of polydiphenylamine.

Thermal oxidation of poly(1-trimethylsilylprop-1-yne) studied by IR spectroscopy

Thermal oxidation of poly(1-trimethylsilylprop-1-yne) was studied by IR spectroscopy in the 20—245 °C temperature interval. In the 20—160 °C temperature range, the reaction proceeds predominantly at the C—Me group as revealed by the decrease in the intensity of the bands of the methyl group bound to the C atom and the appearance of the bands of the hydroperoxide and methylene groups. The decomposition of hydroperoxides produces aldehydes and ethers. At 160—200 °C, oxidation occurs via two routes: at the C—Me and C=C groups, while the Me3Si group remains unchanged. At 230—240 °C, the rate of the reaction occurring at the C=C bond is higher than the rates of the processes involving the MeC and Me3Si groups. The relative content of the structural units was calculated for the samples oxidized at different temperatures. Plausible mechanisms of thermal oxidation of poly(1-trimethylsilylprop-1-yne) were considered on the basis of the data obtained.

Thermal oxidation of poly(ethylene oxide–propylene oxide–ethylene oxide) triblock copolymer: focus on low molecular weight degradation products

The oxidative thermal degradation of poloxamer 407, a poly(ethylene oxide–propylene oxide–ethylene oxide) triblock copolymer, at 50 and 80 °C in air was studied by solid phase microextraction/gas chromatography–mass spectrometry (SPME/GC–MS). At 80 °C, we found that degradation was initiated on the PPO block of the copolymer by three mechanisms involving hydroperoxyl formation and depropagation. 1,2-propanediol,1-acetate; 1,2-propanediol,2-formate; 1,2-propanediol,1-acetate,2-formate and 2-propanone,1-hydroxy were the first degradation products produced. Random chain scissions and a sharp decrease in the molecular weight of the material followed the initiation period. Formic acid and acetic acid, formed upon degradation, participated in esterification reactions leading to the formation of the formate and acetate forms of 1,2-propanediol and ethanediol. Though degradation at 50 °C was much slower, the oxidative mechanisms leading to low molecular weight formates and acetates were the same as those observed at 80 °C.

Thermal oxidation of poly(bisphenol A carbonate) investigated by SEC/MALDI

Thermal oxidation products of poly(bisphenol A carbonate) (PC) generated by heating at 300 and 350 °C, respectively, under atmospheric air, were detected by an hyphenated SEC/MALDI technique. The SEC curves of the thermal oxidised samples showed extensive degradation as a function of heating time, up to the formation of very low mass oligomers. Oxidised PC samples were subjected to SEC fractionation by collecting several fractions which were analysed “ off-line” by MALDI-TOF. The MALDI spectra of the SEC fractions of the thermal oxidised PC samples showed the presence of polymer chains containing acetophenone, phenyl substituted acetone, phenols, benzyl-alcohol and biphenyl terminal groups. The mechanisms accounting for the formation of thermal oxidation products of PC involve the operation of several simultaneous reactions: (i) hydrolysis of carbonate groups of PC to form free Bisphenol A end groups; (ii) oxidation of the isopropenyl groups of PC; (iii) oxidative coupling of phenols end groups to form biphenyl groups. The presence of biphenyl units among the thermal oxidation products confirmed the occurrence of cross-linking processes, which is responsible for the formation of the insoluble gel fraction.

Chemiluminescence from thermal oxidation of poly (2,6-dimethyl-1,4-phenylene oxide)

Chemiluminescence (CL) accompanying the oxidation of poly(2,6dimethyl-1,4-phenylene oxide) in oxygen and decomposition of the products of its pre-oxidation in nitrogen was examined from the viewpoint of the relation to the rate of oxidation. Light emission typically decays in both oxidizing and inert atmosphere from an initial maximum value to some steady value. The initial decay is rather fast. It has been shown that the intensity of the initial CL depends not only on the concentration of oxygen in the surrounding atmosphere but also on the degree of pre-oxidation and on the conditions of exposure of the sample to visible light. The mechanism of the polymer oxidation taking into account the terminal phenoxyl groups, formation of hydroperoxides and the decomposition of charge transfer complexes between oxygen and oxygen in hydroxyl or ether groups is discussed.

Thermal oxidation kinetics for a poly(bismaleimide)

AbstractThe thermal oxidation of poly(bismaleimide) of the F655‐2 type, supplied by Hexcel‐Genin, was studied by isothermal gravimetry at 180, 210, and 240°C and various oxygen pressures ranging from 0 to 1.2 bar. Comparison of various sample thicknesses and visible microscopy observations on bulk aged samples shows that the whole oxidized layer has a depth of about 75 μm at 240°C, 138 μm at 210°C, and 229 μm at 180°C. An attempt was made to build a kinetic model to predict this depth. It is based on a differential equation in which O2 diffusion and its consumption rate, r(C), are coupled, C being the O2 concentration. Its resolution needs two sets of experiments: the first one to determine the O2 diffusivity and solubility in the polymer, and the second one to determine r(C). The mathematical form of r(C) is derived from a mechanistic scheme of radical chain oxidation in which initiation is mainly due to POOH decomposition. This expression contains two kinetic parameters, α and β, the values of which are determined from the experimental curves of mass loss rate against O2 pressure (in the stationary state). The theoretical predictions, at each temperature under consideration, are in excellent agreement with experimental results. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3418–3430, 2001

On the autoaccelerated character of the branched oxidation of polyolefins

AbstractPhotochemical or thermal (at moderate temperatures) oxidation of hydrocarbon polymers is characterised by the existence of a pseudo‐induction period, during which oxidation is autoaccelerated, and a steady state. This latter corresponds to the equilibrium between hydroperoxide (POOH) decomposition and formation processes. All the kinetic schemes of thermal ageing, based on the assumption that POOH decomposition is the only source of radicals (whatever its order), have a common feature : the steady‐state rate is independent of the rate constant of POOH decomposition, as experimentally observed in samples containing variable concentrations of catalytic residues.Experimental data indicate that the duration of the pseudo induction period is proportional to the reciprocal of the POOH decomposition rate constant and independent of any other rate constant. This is an exclusive property of kinetic schemes in which POOH decomposition is unimolecular (whereas termination is bimolecular). The corresponding set of differential equations has been first resolved from the hypothesis of existence of a stationary state for radical concentration. Although this hypothesis is questionable, the corresponding analytical expression appears as a good approximative solution for the general case (no hypothesis of stationary regime). This expression displays interesting predictive properties. Some eventual kinetic implications of spatial heterogeneity of oxidation are examined. Certain variables, for instance the second derivative of the kinetic curve of carbonyl growth (or oxygen absorption), or simply the kinetic curve of mass variation, vary in a non‐monotonous way with exposure time. Consideration of timescale associated to these variations can lead to a quantitative approach of the homogeneity. Schematically, if the characteristic time of non‐monotonous variations is of the order of magnitude of the reciprocal of the rate constant of POOH decomposition or lower, the oxidation can be considered almost homogeneous. In the example under study : experimental data on thermal oxidation of poly(propylene) indicate that these systems are not too far from homogeneous ones.

The thermal oxidation of poly(propylene oxide) and its complexes with LiBr and LiI

The thermal volatilisation of pure poly(propylene oxide) (PPO) is greatly accelerated by oxygen. The process of thermal oxidation is dominated by the initial formation of hydroperoxides, which appear to form at the secondary (in preference to the tertiary) carbon atoms in the polymer backbone. The volatile products of degradation, which include acetaldehyde, acetone and methanol (but not unsaturated hydrocarbons, in contrast to purely thermal decomposition), can be accounted for by decomposition of the hydroperoxides. In the presence of alkali metal salts the conversion of PPO to volatile products during thermal oxidation is strongly retarded. A similar effect was observed previously with poly(ethylene oxide). Stabilisation by the salt can be attributed to a combination of effects: (i) retardation of hydroperoxide formation due to strengthening of C-H bonds adjacent to complexed metal cations, and (ii) chemical decomposition of hydroperoxides by the salt.

Photochemical and thermal oxidation of poly(2,6-dimethyl-1,4-phenylene oxide)

Poly(2,6-dimethyl-1,4-phenylene oxide) (PPE) films were exposed to monochromatic radiation (254 nm, 365 nm) and to polychromatic radiation (λ300 nm, outdoor exposure) in the presence of atmospheric oxygen. Thermooxidation of PPE samples was carried out in the temperature range 100 °C–170 °C. Products formed in irradiated and thermooxidized films were identified by coupling FTIR spectroscopy to chemical derivatization reactions, physical treatments and gas phase analysis. The nature and the distribution of oxidation products are shown to be different in the two conditions of degradation.

Pyrolysis and thermal oxidation of doped and undoped poly(( o-(trimethylsilyl)phenyl(acetylene)

The pyrolysis and thermal oxidation of poly(( o-(trimethylsilyl)phenyl)-acetylene) (poly(TMSPA)) and poly(TMSPA)-organic electron acceptor complexes have been studied. Below 270°C there is no significant interaction between the polymer and O 2. Above 270°C, the weight loss in the presence of O 2 follows a two-step process. Organic electron acceptors interact with poly(TMSPA) in varying degrees, with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) showing the strongest charge transfer interaction. The DDQ dopant retards decomposition and promotes char formation during pyrolysis.

Thermal stability of poly(oxypropylene-ether) polyol

The thermal decomposition and thermal oxidation of poly(oxypropylene-ether) polyol (POPP) have been studied. Thermal oxidation-decomposition in air has been found to be a major factor affecting the thermal stability of POPP. The inhibiting ability of antioxidants of different structures on the thermal oxidation of POPP has been investigated by means of thermal analysis. Experimental results show that phenothiazine, 2,2'-methylene bis(4-methyl-6-tert-butyl phenol) (2246), propyl gallate and pyrogallol are more effective antioxidants. Antioxidant systems consisting of 2246 and triphenyl phosphite. 2.6-di-tert-butyl-4-methyl phenol (264) and phenothiazine, or 2246 and phenothiazine, exhibit better synergistic effects.

Thermal oxidation of poly(ethylene‐co‐carbon monoxide) and polyethylene

AbstractThermal oxidations at 101°C of ethylene‐carbon monoxide (E/CO) copolymer and low‐density polyethylene (DYNK) were studied over the range of 0–30 mL oxygen absorbed per gram of polymer. Relative changes in reaction rates, chemical composition, and molecular weights of the polymers were observed using oxygen uptake, infrared spectroscopy, and gel permeation chromatography. At comparable oxidation rates, differences in concentrations of most functional groups appeared to be small, except for the IR peak attributed to non‐hydrogen‐bonded hydroperoxide which was absent in the spectrum of E/CO copolymer. The extent of scission at comparable oxygen absorption was greater in E/CO than DYNK, since ketonic carbonyl groups were oxidized faster than methylene groups.

Environmental and thermal oxidation of poly(vinyl chloride) and impact‐modified poly(vinyl chloride). I

Environmental and thermal oxidation of poly(vinyl chloride) and impact‐modified poly(vinyl chloride). I

Phosphorescence of thermally oxidised poly(butadiene) and model enones: temperature dependence

The temperature dependence of phosphorescence of model enone compounds in poly (methyl methacrylate) matrix and glassy methylcyclohexane/isopentane solution and of enones formed from thermal oxidation of poly (butadiene) has been studied over the temperature range 77–220°K. The single discontinuity in the plot for the model enone-glassy solvent is due to the freezing of a (solvent perturbed) barrier to rotation in the enone, and an analogous transition is also observed in the model enone poly (methyl methacrylate) samples and in thermally oxidised poly (butadiene). In the polymer matrices, a second transition corresponding to the γ-transition in poly (methyl methacrylate) and the glass transition temperature T g in poly (butadiene) are also revealed in the Arrhenius plots. The results demonstrate that care must be taken in ascribing such discontinuities solely to polymer properties since intrinsic properties of the luminescence probe itself may exhibit similar features.

Thermal oxidation of poly(1-pentene): 1. Indentification of products and mechanisms

Isotactic poly(1-pentene) was degraded in the presence of pure oxygen at 115°C. The functional groups present in the non-volatile products were identified using infra-red spectroscopy. The volatile products formed were identified by means of a relatively new technique which combines thermal and mass chromatography. In this study, fourteen volatile products were detected and identified and their relative abundance estimated. The results obtained could readily be reproduced. Various oxidation mechanisms for these products are postulated.