Kinetics of formalization of poly(vinyl acetate)

Kinetic information on the formation of poly(vinyl formal) by the reaction of poly(vinyl acetate) and formaldehyde in presence of aqueous acid has been derived from the spectroscopic analysis of polymer samples after different periods of reaction. The hydroxyl content of poly(vinyl formal) is found to be nearly independent of reaction time and only slightly affected by temperature while the fall of acetate content and the increase in formal content are most rapid in the initial period and are largely influenced by temperature. The rate expression formulated on the assumption that the formalization reaction is of first order with respect to both poly(vinyl acetate) and formaldehyde explains the observed variation of polymer composition with reaction time. The activation energy for the reaction is found to be 17.3 kcal/mol.     

Grafting onto polyester fibers. II. Kinetics of grafting of acrylic acid,acrylonitrile, and vinyl acetate onto polyester fibers

The kinetics of grafting of acrylonitrile, acrylic acid, and vinyl acetate onto polyester fiber by catalytic initiation and radiation were studied. The energy of activation determined for acrylic acid grafting by the catalytic method was 10.7 kcal/mole and that for vinyl acetate grafting by the radiation method, 11.7 kcal/mole. In the case of acrylonitrile grafting by the catalytic method, the rate of grafting decreased with increase in temperature of grafting, showing the differential behavior of the precipitating type of polymer from that of homogeneous polymerization.     

Thermal degradation of polyvinylchloride in phenolic solvents II

The thermal degradation of polyvinylchloride in 2-allyl phenol, 2-allyl-6-methylphenol and 2-methoxy-4-allyl phenol (eugenol) has been investigated in an atmosphere of nitrogen in the temperature range 188–218°C. The reaction is very slow in eugenol. The activation energy was lower in eugenol (40 kcal/mole) than in 2-allyl phenol (47kcal/mole). The reaction is autocatalytic. The rate of dehydrochlorination in ethylbenzoate or methylsalicylate is suppressed by addition of small quantities of eugenol. The results have been explained on the bases of a free radical mechanism for the dehydrochlorination reaction.     

Kinetic study of the thermal degradation of poly(aryl ether ketone)s containing 2,7‐naphthalene moieties

The degradation of poly(aryl ether ketone) containing 2,7‐naphthalene moieties was subjected to dynamic and isothermal thermogravimetry in nitrogen and air. The dynamic experiments showed that the initial degradation temperature, temperature for 5% weight loss, and temperature corresponding to the maximum degradation rate of poly(aryl ether ketone) containing 2,7‐naphthalene moieties were a little higher than those of poly(ether ether ketone) and almost independent of the 2,7‐naphthalene moiety content. The thermal stability of poly(aryl ether ketone) containing 2,7‐naphthalene moieties in air was substantially less than that in nitrogen, and the degradation mechanism was more complex. The results obtained under the isothermal conditions were in agreement with the corresponding results obtained in nitrogen and air under the dynamic conditions. In the dynamic experiments, the apparent activation energies for the degradation processes were 240 and 218 kJ/mol in nitrogen and air for the second reaction stage as the heating rate was higher than 5°C/min. In the isothermal experiments, the apparent activation energies for the degradation processes were 222 and 190 kJ/mol in nitrogen and air, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermal stability of a novel poly(ether ether Ketone Ketone) (PK99)

The degradation of PK99 was studied by heating the polymer in both isothermal and dynamic conditions under nitrogen flow and in a static air atmosphere. In both environments this polymer's thermal stability exceeded that of PEEK. The dynamic experiments showed that in both nitrogen and air atmospheres the polymer degraded in two stages with formation of the same residue, which was quite stable under nitrogen, while almost completely burned in air. Good agreement was observed with the isothermal experiments. Apparent activation energy values were evaluated. The double linear relationships obtained by the Kissinger equation suggested a complex degradation process.     

Mechanism of degradation of poly(vinyl butyral) using thermogravimetry/fourier transform infrared spectrometry

A TG/FTIR system was used to identify the products of thermal oxidative degradation of PVB, and also to elucidate the mechanism of degradation. This technique is useful in the kinetic analysis of fast reactions such as polymer degradation, unlike the use of a TG/GC/FTIR system, in which long retention times are needed to separate the products. A computer resolution method based on a pattern recognition technique is proposed to resolve the dynamic mixture IR spectra of the degradation products. A four-component synthetic mixture was used to evaluate the performance of the resolution algorithm and was found to be accurate within ±5%. The method was then applied to PVB degradation. The dynamic information of PVB thermal oxidative degradation obtained by resolving the mixture IR spectra was used to elucidate the reaction mechanism and to determine the kinetic parameters. Results showed that PVB degradation in air took place at a temperature 50K lower and the overall activation energy dropped from 338 kJ/mole (in nitrogen) to 200 kJ/mole (in air) compared with the degradation in a nitrogen atmosphere.     

The influence of oxygen on the chemical reactions during stabilization of pan as carbon fiber precursor

DTA measurements were used for studies of the kinetics of the cyclization and oxidation of PAN during the thermal treatment in air and nitrogen. The cyclization is a first order reaction with an activation energy of about 30 kcal/mole in nitrogen and about 34 kcal/mole in air. For copolymer PAN (5% methylacrylate) lower activation energies were found. Oxygen promotes the initiation of the cyclization but does not catalyze the cyclization reaction itself. The sequence of cyclization and oxidation reactions is discussed in detail.     

Hydraulic permeation of liquids through swollen polymeric networks. I. Poly(vinyl alcohol)–water

Poly(vinyl alcohol) membranes were prepared by crosslinking with terephthalaldehyde. Hydraulic permeation of water through this network structure was measured as a function of pressure for temperatures ranging from 18° to 35.8°C. The data were analyzed via a previously developed solution–diffusion theory for hydraulic permeation to give mutual diffusion coefficients. The activation energy for diffusion was found to be 6.5 kcal/mole which compared to the value of 4.3 kcal/mole for viscous flow of water indicates an influence of polymer–liquid interaction on the energetics of the diffusion process.     

Pyrolysis kinetics of highly crosslinked polymethylsiloxane by TGA

The pyrolysis kinetics of highly crosslinked polymethylsiloxane (PMS) was investigated by thermogravimetric analysis (TGA) under both isothermal and elevated temperature conditions with several environmental gases, such as oxygen, nitrogen, air, and helium. A non-chain-scission mechanism composed of initiation, propagation, and termination was proposed to interpret the thermal degradation of highly crosslinked PMS. The mechanism was verified by the experimental results under isothermal conditions. The activation energy of initiation, E_i, was about 20–30 kcal/mol and the activation energy of propagation, E_p, was about 4–6 kcal/mol. These activation energies were found to be different for different gases. The activation energy of initiation for PMS in an aggressive atmosphere, such as oxygen, was lower than that in an inert atmosphere, such as nitrogen. But the activation energy of propagation for PMS was higher in an active environment than in an inert one. There were no direct conclusions about the thermal degradation of highly crosslinked PMS at elevated temperature. Based on thermogravimetric experiments, it is suggested that a pyrolysis process be conducted with a rate of temperature increase less than 10°C/min for preparing the silicon base inorganic membrane.     

Estimation of butadiene in vulcanized BR and SBR by thermographic analysis

A method for the determination of butadiene in vulcanized polybutadiene (BR) and styrene–butadiene rubber (SBR) has been proposed. The method is based on determining the area under the exothermic peak (around 380°C) of the differential scanning calorimetry thermograph in nitrogen. The exotherm area was found to be linearly related to the butadiene content of the polymers and was unaffected by vulcanization or by loading with carbon black. This approach supplements and extends the existing methods of BR determination, which depend upon the estimation of styrene content. The existing evidence indicates that the exothermic reaction is due to cyclization of BR. The energy of activation calculated from the Arrhenius plot is 32–35 kcal/mole; it does not change with vulcanization, loading, or nature of the polymer.     

A thermal analysis study of bisphenol-A-polycarbonate–dimethylsiloxane block copolymers

The thermogravimetric analysis (TGA) of three block copolymers of poly(dimethylsiloxane)–Bisphenol-A-polycarbonate was measured in nitrogen and air from just above room temperature to 1000 K. Measurements were made on a Perkin-Elmer TGS-2 system equipped with a System 4 microprocessor controller. Weight loss curves were obtained for heating rates ranging from 1.5 (or lower) to 80°C/min. Results were analyzed according to the method of Flynn and Wall. Two degradation reactions were observed in air and in nitrogen, respectively. In air, the activation energy was found to be 28–35 kcal/mol. In the inert atmosphere, activation energies were 44±3 kcal/mol and 11–27 kcal/mol, respectively. No straightforward relationship was found between the thermal stability of the copolymers and their composition. The morphology of char residues formed at 80°C/min heating rate to 1000 K have been examined in relation to the Si content. The degree of char formation at different heating rates has been established in nitrogen and in air, respectively.     

Synthesis of poly(vinyl butyral)s in homogeneous phase and their thermal properties

The condensation reaction of butyraldehyde (BA) with poly(vinyl alcohol) (PVA) to give poly(vinyl butyral) (PVB) was studied in detail using N‐methyl‐2‐pyrrolidone (NMP) as solvent for PVA and PVBs. PVBs having various degrees of acetalization were obtained. The acetalization reaction under a variety of conditions gave at best a polymer with 97% acetalization. The extent of modification and the structure of the polymer, i.e., the ratio of acetal units from meso and racemic dyads of PVA, were determined by ¹H‐NMR. The acetalization degree was reflected in the solubility of PVB; all products were soluble in NMP. PVBs were characterized by IR spectroscopy and ¹H and ¹³C‐NMR. The glass transition temperatures of PVBs, determined by DSC, increased as vinyl alcohol units increased and displayed a positive departure from linearity. Thermal degradation of PVBs was studied using differential thermal analysis (DTA) and thermogravimetry (TGA) under dynamic conditions in nitrogen. The content of hydroxyl groups had an effect on the thermal stability of PVBs; the thermal stability of PVBs decreased as vinyl alcohol units increased. The apparent activation energy of the decomposition was determined by the Kissinger and Flynn–Wall methods, which agree well. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5007–5017, 2006     

High‐resolution thermogravimetry of poly(4‐methyl‐1‐pentene)

Thermal degradation and kinetics of poly(4‐methyl‐1‐pentene) were investigated by nonisothermal high‐resolution thermogravimetry at a variable heating rate. Thermal degradation temperatures are higher, but the maximum degradation rates are lower in nitrogen than in air. The degradation process in nitrogen is quite different from that in air. The average activation energy and frequency factor of the first stage of thermal degradation for the poly(4‐methyl‐1‐pentene) are 2.4 and 2.8 times greater in air than those in nitrogen, respectively. Poly(4‐methyl‐1‐pentene) exhibits almost the same decomposition order of 2.0 and char yield of 14.3–14.5 wt % above 500°C in nitrogen and air. The isothermal lifetime was estimated based on the kinetic parameters of nonisothermal degradation and compared with the isothermal lifetime observed experimentally. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2201–2207, 1999     

The thermal decomposition of poly(vinylidene chloride) in the solid state

The rate of decomposition of PVDC is sensitive to differences in the method of preparation of the polymer. Polymers prepared by mass polymerization of very pure monomer were most stable. Emulsion polymerized PVDC degraded the fastest. The activation energy for the latter was 34.4 kcal/mole. Over the range of 130°–190°C, the rate of decomposition increases with reaction time to ～10% HCl evolved. Beyond this point, the reaction follows first-order kinetics. The first-order rate is independent of molecular weight. Lamellar crystals of PVDC degrade at a higher rate than “as polymerized” powders. This may be due in part to annealing of the crystals in the degradation temperature range; but it also results from a sensitization of the polymer to thermal degradation from exposure to the polar solvents used for recrystallization. A mechanism is proposed to account for these observations.     

Oxidation Kinetics of Participate Silicon Monoxide

The air oxidation of particulate silicon monoxide to cristobalite was studied in the range 820° to 1040°C. This SiO neither disproportionates nor volatilizes in this range. An activation energy of 23.8 ± 2.0 kcal/mole for the diffusion of oxygen was obtained from a measure of the differential rate of reaction at various temperatures for various fixed percents of conversion up to 24%. The reciprocal time needed to reach a fixed percent of conversion up to 30%, at various temperatures, gave an activation energy of 24.2 ± 1.5 kcal/mole. It is concluded that the diffusional activation energy is 24.0 ± 2.0 kcal/mole.     

Thermal degradation of polyvinyl chloride in phenolic solvents I

The thermal degradation of polyvinyl chloride in phenolic solvents has been investigated in an atmosphere of nitrogen in the temperature range 137–206°C. The solvents used were phenol, o-cresol, methyl, ethyl, amyl, and phenyl salicylates. The reaction was fast in phenol and slow in amyl salicylate. The rate of dehydrochlorination decreased with increasing size of the alkyl side chain in salicylates. The activation energy was low in amyl salicylate (26 kcal/mole) and high in o-cresol (29 kcal/mole), and for other solvents it was in between these two values. The results have been explained as being due to the variation in the reactivity of phenolic hydrogen and to steric factors of the various substituents.     

Thermogravimetric analysis of blends of low‐density polyethylene and poly(dimethyl siloxane) rubber: The effects of compatibilizers

The thermal stability of vulcanizates of low‐density polyethylene (LDPE), poly(dimethyl siloxane) (PDMS) rubber, and their blends was studied by nonisothermal thermogravimetry. Four ethylene copolymers [ethylene methyl acrylate (EMA), ethylene vinyl acetate, ethylene acrylic acid, and a zinc‐salt‐based ionomer (Lotek 4200)] were used as compatibilizers for the blend systems. The thermograms and derivatograms of the blends showed that thermal degradation took place in two stages, whereas those for the base polymers showed single‐stage degradation. Kinetic studies of the blends and pure components showed that the degradation followed first‐order reaction kinetics. The activation energy at 10% degradation was determined with the Freeman–Carroll method and was at a maximum (42.34 kcal/mol) for the 25:75 LDPE/PDMS rubber blend. The half‐life at 200°C was evaluated by the Flynn–Wall method and was at a maximum (812.5 days) for the same blend. Out of four compatibilizers, EMA showed the maximum activation energy (34.25 kcal/mol) for degradation and a maximum half‐life (695.3 days), indicating that EMA was the best compatibilizer for the blend system. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 635–642, 2003     

Epoxy resins. I. The stability of the epoxy–trimethoxyboroxine system

The useful life of a material depends on its environmental exposure. The diglycidyl ether of bisphenol A (DGEBA) cured with trimethoxyboroxine (TMB) was evaluated under various aging conditions. For isothermal aging, the main factor controlling weight loss appeared to be related to the diffusion of the degradation products (E_act = 22.1 kcal/mole). Chemical decomposition kinetic parameters were obtained using vacuum thermogravimetric analysis (TGA) on powder samples. The thermal decomposition activation energy and the reaction order of cured DGEBA were 37.5 kcal/mole and 1.05, respectively. The hydrolytic aging of this material was also kinetically analyzed, and it was concluded that the weight change was controlled by both water diffusion into the sample and diffusion of hydrolysis products from the sample. During hydrolytic aging below the glass transition temperature, the specimens gained weight up to 0.05 g based on 1-g unaged cured resin and then leveled off. At higher temperatures, the specimens initially gained weight and then began to lose weight, reaching a constant weight gain. The activation energies for water diffusion into the cured resin are 19.5 kcal/mole at temperatures above T_g and 21.5 kcal/mole at temperatures below T_g. The main hydrolysis product was boric acid from reaction of the boroxine ring with water. The time-temperature superposition principle was used for the weight loss study on isothermal and isothermal hydrolytic aging. The scale factor in this approach was found to be the ratio of the diffusion coefficient at the temperature of interest to that at a reference temperature.     

A dynamic mechanical study of the curing reaction of two epoxy resins

The curing behavior of two commercially formulated epoxy resins composed of the tetrafunctional amine dicyandiamide and with differing epoxy components, 4,4′-bisglycidylphenyl-2,2′-propane and the tetraglycidyl ether of methylene dianiline, is characterized by dynamic spring analysis. This supported viscoelastic technique is well suited to the determination of the onset of gelation under isothermal conditions but the method is not useful for monitoring later stages of reaction when the resins become more rigid. The activation energy for the curing of the two resins is about 87 kJ/mole (20.7 kcal/mole). Rate constants for the first order curing reaction are given. Additional studies of films cured below the ultimate T_g show that two relaxations can be observed upon heating. The first relaxation occurs near the original isothermal cure temperature with a low activation energy, about 250 kJ/mole, whereas the second relaxation occurs near the ultimate T_g, under the conditions used here, with an activation energy of 500–650 kJ/mole. It is believed that these activation energies provide a unique method of characterizing the molecular mobility of epoxy resins at various states of cure.     

Kinetics of the reaction between urea and formaldehyde in the presence of sulfuric acid

The kinetics of the reaction between urea and formaldehyde were studied in the presence of various amounts of sulfuric acid (5–45% by weight) at different temperatures (5°, 15°, and 25°C). The reaction was shown to follow first-order kinetics. The activation energy for the reaction varies from 12.51 kcal/mole to 14.59 kcal/mole in the range of sulfuric acid concentration studied.