Temperature dependence of processes during initial stages of oxidation of poly(acrylonitrile-co-acrylic acid) films

Poly(acrylonitrile-co-acrylic acid) films containing 1.8 percent acrylic acid as comonomer units in the copolymer were oxidized in air isothermally at different temperatures for periods of 1 and 5 hours. The physico-chemical properties such as thermogravimetry, differential scanning calorimetry, infrared spectral absorption and intrinsic viscosity were analysed for the oxidized films. The intrinsic viscosity shows that the molecules of the polymer crosslink at temperature as low as 100°C. TGA spectrum shows two regions of steep weight losses in the range of temperatures studied, one is at 275–300°C and the other at 395–485°C. The first region is the formation of ladder polymer with the elimination of NH₃, HCN and CO. The second region is due to the formation of aromatic structures with the elimination of HCN, NH₃, water vapour and higher hydrocarbons. DSC spectral analysis shows an endothermic effect up to 205°C and exothermic processes from 205–300°C with a peak at 276°C. The exothermic processes continue up to 360°C. The exothermic effect is reduced for the films oxidized at 242 and 275°C. A marked endothermic effect is noticed at 120°C for the films oxidized at 242 and 275°C. This shows that the cyclization accompanying with exothermic effect sufficiently advanced during isothermal treatment leaving less room for rapid cyclization occurring upon further heating. IR spectral data show the negative environment with a shoulder at 2210 cm^?1 which is associated with uptake of oxygen during oxidation. Distinct peaks at 810 and 1550–1700 cm^?1 are noticed for the oxidized films oxidized at 275°C which are due to the presence of conjugated double bonds of the type C ? N? C ? N. This type of conjugation is assumed in the ladder polymer.     

Thermal decomposition of poly(oxytetramethylene) glycol

Studies of thermal decomposition on poly(oxytetramethylene) glycol have been conducted by pyrolysis gas chromatography–mass spectrometry, infrared spectroscopy, and thermogravimetric anaylysis (TGA). The major volatile decomposition products are suggested to be a series of molecules made up by the repetition of oxytetramethylene with formyl and/or methyl ends. Absorption peaks, associated with formyl appear in infrared spectrum of a sample preheated at 523°K lower than the onset temperature obtained from the TGA curve. The isothermal TGA curves fit well to the Shimha rate equation for the random decomposition of polymers. The proper activation energies obtained from the thermally controlled and the isothermal TGA data are approximately 60–70 kJ mol⁻¹ and lower than those for other polymers in ordinary thermal decomposition. These data suggest that the major reaction in the thermal decomposition of poly(oxytetramethylene) glycol is an ether cleavage. Two pathways, a radical scission accompanied by β‐hydrogen transfer and a nonradical reaction through a four‐membered ring transition state, are proposed and discussed for the ether cleavage. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1538–1544, 2000     

Synthesis,polymerization, and copolymerization of aliphatic vinyl azide

The synthesis and characterization of a fully aliphatic polymeric azide by polymerization of its vinyl monomer 1,3‐diazidoisopropyl methacrylate (DAIPM) is reported. DAIPM was prepared by azidation of epichlorohydrin followed by coupling with methacrylic acid. Homopolymer and copolymers with methyl methacrylate were prepared and characterized by IR, GPC, TGA, DTA, and elemental analyses. These polymers are freely soluble in organic solvents like dichloromethane, tetrahydrofuran, dimethyl formamide, acetone, and so forth and do not crosslink on storing. The polymers show decreased thermal stability with an increase in azide content and undergo exothermic decomposition on heating. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1852–1857, 2003     

Kinetic analysis of high-resolution TGA variable heating rate data

Isothermal and constant heating rate thermogravimetric analysis (TGA) experiments have been performed for examining decomposition of polymers and composites. In practice, low heating rates are necessary to obtain good resolution under nonisothermal conditions thus increasing the time required for experiments. A novel TGA mode, high-resolution TGA (Hi-Res^TM TGA), provides a means to remarkably increase the resolution while often decreasing the time required for experiments. In this variable heating rate mode of Hi-Res^TMTGA, the heating rate is continuously and dynamically varied to maximize resolution. Thus, traditional methods cannot be directly utilized to determine kinetic parameters. Accordingly, in this work, variable heating rate experiments were run on ethylene-vinylacetate (EVA) copolymer, poly(ether ether ketone) (PEEK), and carbon-fiber-reinforced bismaleimide (BMI), whose kinetics have been quantitatively described with traditional isothermal and nonisothermal experiments. Comparison of the different techniques led to the development of a simplified method by which the activation energy, preexponential factor, and reaction order can be extracted from variable heating rate TGA experiments. The technique, based on the principle that maximum weight loss rate is observed at minimum heating rate, gave kinetic results that were in excellent agreement with values that have been determined by traditional isothermal and dynamic experiments. © 1993 John Wiley & Sons, Inc.     

Thermal degradation studies of several pyrrone films

The thermal degradation of several polyimidazopyrrolone (pyrrone) films was studied in air and in vacuum over the range of 100–1000°C. by thermogravimetric analysis (TGA), with the use of both isothermal heating and programmed heating rates of 2, 3, 5, and 7.5°C./min. At pressures of 10^?6 torr or less, maximum weight losses average 30% at 800°C. Rates of volatilization and activation energies were derived to provide comparison between these ladder-type polymers. Mass spectrometric analysis of the pyrolysis gases evolved under vacuum conditions showed that CO, CO₂, and H₂O were the primary volatile products and that they were formed throughout the period of weight loss. Approximate correlation between changes in weight and changes in the total pressure for the vacuum tests indicates that mass spectrometric results could provide quantitative as well as qualitative data. The importance of sample history prior to heating and of sample geometry in developing meaningful and reproducible TGA results is aptly demonstrated. The ability of these materials to absorb readily 5–7 wt.-% of water under ambient conditions and the effect of this property upon weight loss measurements are shown.     

Properties of CP: Coefficient of Thermal Expansion,Decomposition Kinetics,Reaction to Spark,Friction and Impact

The properties of pentaamine (5‐cyano‐2H‐tetrazolato‐N2) cobalt (III) perchlorate (CP), which was first synthesized in 1968, continues to be of interest for predicting behavior in handling, shipping, aging, and thermal cook‐off situations. We report coefficient of thermal expansion (CTE) values over four specific temperature ranges, decomposition kinetics using linear and isothermal heating, and the reaction to three different types of stimuli: impact, spark, and friction. The CTE was measured using a Thermal Mechanical Analyzer (TMA) for samples that were uniaxially compressed at 68.95 MPa and analyzed over a dynamic temperature range of −20 °C to 70 °C. Differential scanning calorimetry, DSC, was used to monitor CP decomposition at linear heating rates of 1–7 °C min⁻¹ in perforated pans and of 0.1–1.0 °C min⁻¹ in sealed pans. The kinetic triplet was calculated using the LLNL code Kinetics05, and predictions for 210 °C and 240 °C are compared to isothermal thermogravimetric analysis (TGA) experiments. Values are also reported for spark, friction, and impact sensitivity.     

Influence of heating rate on the pyrolysis of oil shale

The decomposition of oil shale from the Kvarntorp deposit in Sweden has been investigated using isothermal and non-isothermal methods. It was found that the heating rate during the initial non-isothermal period in the isothermal experiments had a considerable effect on the rate of devolatilization. At heating rates in the order of 10⁵°C/s the total weight loss exceeded the weight loss predicted from the volatile matter according to a proximate analysis.The effect of particle and sample size on the rate of decomposition (weight loss) was studied and found to have a significant influence at heating rates of the order of 10⁵°C/s while no effect was detected at heating rates around 200 °C/s (isothermal) or below 50°C/min (non-isothermal). The decomposition at low heating rates was completed at temperatures below 600°C and about 50 percent of the devolatilization could be described by first order kinetics with an apparent activation energy of 130 KJ/mole.At heating rates of 200°C/s (isothermal) the decomposition could also be described by simple first order kinetics but with an activation energy of 67 KJ/mole, thus indicating a different rate-determining mechanism.     

Synthesis and characterization of cubane polyamides

Cubylamines and cubylmethylamines are of interest as antiviral agents. Reliable syntheses of some polyamides with cubane as the backbone of a polymer chain are described. Two monomers of cubane, cubane‐1,4‐dicarboxylic acid (CDA) and 1,4‐diaminocubane (DAC), are used. Polymerizations of DAC, 1,6‐hexamethylene diamine and 1,4‐diaminobenzene with cubane‐1,4‐dicarbonyl chloride, adipoyl chloride and terephthaloyl chloride to obtain polyamides are discussed. The polymers were characterized by FTIR, ¹H NMR and ¹³C NMR spectroscopies. Characterization of the prepared polyamides by TGA and DSC show a highly exothermic peak above 200 °C. Hydrolysis of polyamides containing DAC were carried out in dialysis bags containing an aqueous buffer solution (pH 8) at 37 °C. Detection of the hydrolysis product by UV spectroscopy showed that DAC was released by the hydrolysis of the amide bonds in the polymer chain. © 2000 Society of Chemical Industry     

Heat-resistant thermosetting polyimide matrix resins containing keto,ether, hexafluoroisopropylidene linkages and maleimido- and nadimido- end capped groups

Various heat-resistant thermosetting polyimides containing hexafluoroisopropylidene and keto and ether groups suitable for fiber-reinforced composites development have been synthesised by thermal polymerization of maleimido and nadimido end capped polymer precursors. Thermal polymerization involving addition reactions was performed at 225°C for 1.5 h and post-curing at 290°C for 0.5 h. Tough polymers XVIII to XXIII were obtained. The thermal polymerization was monitored using infrared spectroscopy. The polymer precursors were characterized by IR, ¹H-NMR, and elemental analysis. The synthesized polymers were evaluated for thermal stability using dynamic thermogravimetric analysis (TGA). All the polymers showed thermal decomposition temperatures in the range of 430–435°C in nitrogen and in air. The char yield of the polymers was in the range of 60–67% in nitrogen at 800°C. This study indicated that thermally synthesized polymers from hexafluoroisopropylidene, keto, and ether containing polymides are potential candidates for the development of advanced materials for aerospace and high-tech applications. © 1993 John Wiley & Sons, Inc.     

Thermal analysis of poly(1,3,4-oxadiazole-2,5 diyl-1,2-ethenediyl) and poly(1,4-phenylene-1,3,4-oxadiazole-2,5 diyl-1,2 ethendiyl)

Poly(1,3,4-oxadiazole-2,5-diyl-1,2-ethendiyl) and poly(1,4-phenylene-1,3,4-oxadiazole-2,5 diyl-1,2-ethenediyl) have been prepared by condensation polymerization using fuming sulfuric acid and different quantities of terephthalic acid (T), fumaric acid (F), and hydrazine sulfate (HS). Homopolymers of F and T and various copolymers of F:T have been prepared. The polymer structure was investigated by IR and visible-range spectra and elemental analysis. The existence of poly(1,3,4-oxadiazole-diylphenylene) and poly(hydrazoterephthaloyl) structures was revealed by these studies. These polymers were thermally stable, and most of them did not show a weight loss below 350°C. The relative thermal stabilities of the various polymers have been evaluated by “integral procedural decomposition temperature” and activation energy measurements.     

Depolymerization of waste polybutylene terephthalate in hot compressed water in a fused silica capillary reactor and an autoclave reactor: Monomer phase behavior,stability, and mechanism

Depolymerization is a potentially viable means of recycling waste polymers, converting them back into monomers or other useful compounds. Terephthalic acid (TPA) and 1,4‐butanediol (1,4‐BD) are the depolymerization monomer products of polybutylene terephthalate. Their yields from depolymerization in hot compressed water (HCW) were previously found to be lower than reported theoretical values. Thus, the phase behavior, stability, and mechanism of monomers in HCW were investigated in a fused silica capillary reactor (FSCR) and a stainless steel autoclave reactor. Phase change observations showed that TPA was completely dissolved in water at 300°C, was relatively stable at 320 to 350°C, and that its recovery significantly decreased at temperatures above 350°C. The decomposition of TPA increased with increasing heating time. However, the recovery of 1,4‐BD decreased rapidly with increasing temperature or heating time. A mechanism for the stability of TPA and 1,4‐BD is proposed based on their depolymerization products. The products were quantified by Fourier transform‐infrared spectroscopy, high‐performance liquid chromatography, and gas chromatography coupled with mass spectrometry. The wall effect of the stainless steel autoclave promoted the decomposition of TPA and 1,4‐BD in HCW. POLYM. ENG. SCI., 57:544–549, 2017. © 2016 Society of Plastics Engineers     

Antioxidant Activity of Amaranth Protein Hydrolysate Against Thermal Oxidation of Vegetable Oils

The antioxidant capacity of amaranth protein hydrolysate (AH) during the thermally induced oxidation of two different vegetable oils, sunflower oil (SO) and canola oil (CO), was assessed by differential scanning calorimetry by means of isothermal and non‐isothermal assays. Interactions between AH and tocopherols were also analyzed. In both oils, AH (10 % w/w) produced an increase in the induction period in isothermal assays, presenting a synergistic effect with tocopherols. In the case of non‐isothermal assays, thermograms of oils with AH showed a significant diminution in the second exothermic peak, suggesting an inhibition of the decomposition of primary to secondary oxidation products. In addition, AH produced an increase in the oxidation rate constant (k) value at low temperatures being more evident in the case of canola oil. However, this effect decreased as a function of the temperature increase, which suggests that AH would have a pro‐oxidant effect at low temperatures but a heat stabilizing effect at high temperatures (above 210 °C for SO and 190 °C for CO).     

Synthesis and decomposition performance of a polymeric foaming agent containing a sulfonyl hydrazide moiety

A new monomer, methacryloyloxybis(benzenesulfonyl hydrazide) (MAOBSH) containing a foamable sulfonyl hydrazide functional group after decomposition by heating, was synthesized from 4,4′‐oxybis(benzenesulfonyl hydrazide) (OBSH) with methacryloyl chloride, and used to obtain poly(MAOBSH) as a polymeric foaming agent (PFA) in dry tetrahydrofuran at 70 °C using azobisisobutyronitrile as an initiator. The structures of the synthesized MAOBSH and poly(MAOBSH) were identified using Fourier transform infrared and ¹ H NMR spectroscopies. The decomposition temperature of poly(MAOBSH) was determined to be 245 °C and this temperature was decreased to around 160 °C by adding an activator such as surface‐treated urea to the polymer. The exothermic temperature and heat determined by the decomposition of the polymer were 256 °C and 287 J g^?1. The amount of gas evolution for poly(MAOBSH) measured at the decomposition temperature was 74 mL g^?1. Furthermore, polymers incorporating the PFA showed better skin and finer cell structure as well as better mechanical properties such as elongation and compression set than polymers with added OBSH due to the better compatibility of the developed PFA with polymers. © 2012 Society of Chemical Industry     

Thermal and mechanical properties of the precursor polymers: Comparison of their properties with poly(amic acid)

The DSC thermograms of P-PHA show a large endothermic peak at 450–550°C. As the annealing temperature increases from 250°C to 400°C, the endothermic peaks become smaller and then disappear for samples annealed above 450°C. As observed for P-PHA, the endothermic enthalpy of PHA and PAA became smaller with an increasing annealing temperature. The cyclization onset temperature (T₁) of the three precursors increases linearly with an increasing annealing temperature at a constant annealing time (30 min). Otherwise, the initial decomposition onset temperature (T₂) was shown to be constant. T₂ of P-PHA, PHA, and PAA were observed in the temperature ranges of 601–603°C, 576–577°C, and 532–534°C, respectively. These TGA results confirm that all of the samples are thermally stable. Increasing the annealing temperature of the three precursor polymers significantly increases the tensile properties of the films. The tensile properties of all annealed precursors were much higher than those of the unannealed films. In contrast, the initial modulus of PAA is improved only slightly when compared with the other two polymers regardless of the heat treatment. The biaxial stresses in the PHA and PAA films were investigated by holographic interferometry. The stresses in the films were 6.85–7.61 MPa for PHA and 27.01–27.70 MPa for PAA.     

Characterization of sulfur-cured styrene–butadiene copolymer rubbers and their polybutadiene blends

Dissolution of sulfur-cured, carbon black-loaded copolymers and their blends with cis-1,4-polybutadiene (PBD) are brought about by boiling with o-dichlorobenzene which contains a small amount of 2,2′-dibenzamidodiphenyl disulfide. The resulting slurries are subjected to a sequence of separations which include high-speed centrifugation to remove solids, and solvent precipitation followed by filtration to isolate the precipitates. The precipitates are washed with solvent to remove soluble organic materials followed by carbon disulfide washing to dissolve the polymers. Cast films of the polymers are obtained by evaporating the carbon disulfide washings onto sodium chloride discs. The infrared spectra of the cast films of these preparations are very similar to those of their respective polymers prior to loading and curing. Calculations for relative concentrations of bound styrene and PBD microstructures permit nominal identification of the kinds of styrene–butadiene rubber and the amounts of cis-1,4-PBD used in a cured rubber formulation. Absorption bands used are near 3.35 μ for cis-1,4-PBD, 6.65μ for bound styrene, 10.35 μ for trans-1,4-PBD; and 11.0 μ for vinyl-1,2-PBD. Efforts are being made to improve the data by using a grafting infrared instrument and also to extend the calibrations to include other rubber blends.     

Vulcanization of polychloroprene rubber. I. A revised cationic mechanism for ZnO crosslinking

Data relating to the vulcanization of mercaptan‐grade polychloroprene (CR) by ZnO and MgO (alone or in combination) are examined. Compounds were vulcanized through the isothermal heating of samples at 140°C in a laboratory press and at programmed rates in a differential scanning calorimeter. The reaction was stopped at various points during the heating process. The crosslink densities were determined via swelling. Extractable ZnCl₂ and MgCl₂ were analyzed by atomic absorption spectrometry. Three different crosslinking processes were identified. The first crosslinking process involved the activation of the highly reactive tertiary allylic 1,2‐units along the polymer chain, whereas the second and third crosslinking processes were attributed to the activation toward crosslinking of 3,4‐ and 1,4‐units, respectively. The crosslinking reactions of the 1,2‐units comprised three distinct steps: isomerization (promoted by ZnO), dechlorination, and crosslinking. ZnCl₂ (which formed during compounding and upon crosslinking) promoted crosslinking, and its addition to formulations decreased but did not eliminate the induction period before crosslinking. MgO retarded the crosslinking process by limiting the formation of ZnCl₂ during mixing. The results of the CR/ZnO system are discussed, and a modified cationic mechanism for crosslinking is proposed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

New poly(bisbenzoylamine imide) series: Synthesis and characterization

Three new series of poly(bisbenzoylamine imide)s, incorporating different aromatic diamines, have been synthesized. The polymers, obtained by the two-step procedure, have been characterized by DSC, TGA, X-ray, FTIR, and ¹H-NMR methods. Thermal analysis showed glass transition temperatures in the range of 200°–250°C and decomposition at 430°–495°C. Most DSC runs displayed an exothermic event above T_g that was due to cold crystallization of the polymer molecules. A melting point was not observed. The new polymers, even before annealing, showed sharp X-ray diffraction patterns, evidence of semicrystallinity. The polymers, soluble in polar solvents, were analyzed by NMR in solution. Typical chemical shifts for the bisbenzoylamine protons were reported; FTIR spectra showed the characteristic imide peaks. Due to a near overlap of the carbonyl vibration of the imide group with the bisbenzoylamine carbonyl, the latter vibration was detected in only one series. © 1993 John Wiley & Sons, Inc.     

Investigation of the thermal stability of nitroxide capped polystyrene by TGA and Py-GC/MS

The thermal stability of nitroxide capped polystyrene is examined by TGA and pyrolysis-GC/MS. As opposed to technical polystyrene, these polymers (M_n > 30000 g mol^–1) show a characteristic decomposition step at 230–250°C. The volatile product of this step is mainly styrene, which results from retropolymerization. For some PS-N adducts terminator fragments can be identified. Prolonged isothermal treatment of PS-N adducts at their step temperature yields polystyrene without nitroxides. The loss of molecular weight is in the range of technical PS by the same treatment, but the polymers keep a narrow molecular weight distribution.     

The influence of extent of polymerization on the thermal behavior of an epoxy-based polyether resin

A number of studies have been reported in the literature on the polymerization and thermal decomposition of epoxide resins. Lee¹ and Anderson² have both studied the thermal decomposition of epoxy resins, and they concluded that the characteristic exothermic peak (which can occur anywhere between 300° and 400°C) is caused at least partially by some reaction of the epoxide group. We have been investigating the thermal decomposition of an aromatic polyether resin which is produced by curing the diglycidyl ether of bisphenol A (Epon 825) with the catalytic agent trimethoxyboroxine (Fig. 1). DTA studies of the polyether in an inert atmosphere of N₂ showed exothermic peaks at approximately 390°, 430°, and 470°C, with the major exotherm being the one at 430°C. Our investigation has shown the important role played by low molecular weight epoxides in these exothermic reactions.     

Blends of bisphenol A‐based cyanate ester and bismaleimide: Cure and thermal characteristics

A dicyanate ester, namely, 2,2‐bis‐(4‐cyanatophenyl)propane, and a bismaleimide, namely, 2,2‐bis[4‐(4‐maleimido phenoxy)phenyl]propane, possessing closely resembling backbone structures, were cured together to derive bismaleimide–triazine network polymers of varying compositions. The blend manifested a eutectic melting behavior at a 1 : 1 composition with a eutectic melting point of 15°C. The cure characterization of the blends was done by DSC and dynamic mechanical analyses (DMA). The near simultaneous cure of the blend could be transformed to a clear sequential one by catalyzing the dicyanate cure to lower temperature using dibutyl tin dilaurate. The two‐stage, independent cure of the components of the blend evidenced in DSC was confirmed by DMA. The cure profile of the bismaleimide component predicted from the kinetic data derived from nonisothermal DSC was found to be in league with the isothermal DMA behavior. Both techniques led to optimization of the cure schedule of the blends. The cured polymers were characterized by FTIR and TGA. The cured blends underwent decomposition in two stages, each corresponding to the polycyanurate and polybismaleimide. Enhancing the bismaleimide component did not alter the initial decomposition temperature, but led to reduced rate of thermal degradation at higher temperature. Interlinking of the two networks and enhancing crosslink density through coreaction of the blend with 4‐cyantophenylmaleimide unaffected the initial decomposition properties but was conducive for increasing the char residue significantly. Computation of activation parameters for the thermal decomposition of the polymers confirmed that the first step in the degradation of the blends is caused by the polycyanurate component. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3365–3375, 1999