Thermooxidative degradation of methyl methacrylate‐graft‐natural rubber

The thermooxidative degradation of methyl methacrylate‐graft‐natural rubber (MG) at different heating rates (B) has been studied with thermogravimetric analysis in an air environment. The results indicate that the thermooxidative degradation of MG in air is a one‐step reaction. The degradation temperatures increase with B. The initial degradation temperature (T_o) is 0.697B + 350.7; the temperature at the maximum degradation rate, that is, the peak temperature on a differential thermogravimetry curve (T_p), is 0.755B + 368.8; and the final degradation temperature (T_f) is 1.016B + 497.4. The degradation rates at T_p and T_f are not affected by B, and their average values are 46.7 and 99.7%, respectively. The maximum thermooxidative degradation reaction rate, that is, the peak height on a differential thermogravimetry curve (R_p), increases with B. The relationship between B and R_p is R_p = 2.12B + 7.28. The thermooxidative degradation kinetic parameters are calculated with the Doyle model. The reaction energy (E) and frequency factor (A) change with an increasing reaction degree, and the variational trends of the two kinetic parameters are similar. The values of E and A increase remarkably during the initial stage of the reaction, then keep relevantly steady, and finally reach a peak during the last stage. The velocity constants of the thermooxidative degradation vary with the reaction degree and increase with the reaction temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1227–1232, 2003     

Thermogravimetric analysis of methyl methacrylate‐graft‐natural rubber

The thermal degradations of methyl methacrylate‐graft‐natural rubber (MG) at different heating rates (B) in nitrogen were studied by thermogravimetric analysis. The results indicate that the thermal degradation of MG in nitrogen is a one‐step reaction. The degradation temperatures increase along with the increment of heating rates. The temperature of initial degradation (T₀) is 0.448B + 362.4°C, the temperature at maximum degradation rate, that is, the peak temperature on a differential thermogravimetric curve (T_p) is 0.545B + 380.7°C, and the temperature of final degradation (T_f) is 0.476B + 409.4°C. The degradation rate at T_p is not affected by B, and its average value is 48.9%; the degradation rate at T_f is not affected by B either, and its average value is 99.3%. The reaction order (n) is 2.1 and is not affected by B. The reaction activation energy (E) and the frequency factor (A) increase along with B, and the apparent reaction activation energy (E₀) is 254.6 kJ/mol. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2952–2955, 2002     

Thermal analyses of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)

Thermal analyses of poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(HB–HV)], and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) [P(HB–HHx)] were made with thermogravimetry and differential scanning calorimetry (DSC). In the thermal degradation of PHB, the onset of weight loss occurred at the temperature (°C) given by T_o = 0.75B + 311, where B represents the heating rate (°C/min). The temperature at which the weight-loss rate was at a maximum was T_p = 0.91B + 320, and the temperature at which degradation was completed was T_f = 1.00B + 325. In the thermal degradation of P(HB–HV) (70:30), T_o = 0.96B + 308, T_p = 0.99B + 320, and T_f = 1.09B + 325. In the thermal degradation of P(HB–HHx) (85:15), T_o = 1.11B + 305, T_p = 1.10B + 319, and T_f = 1.16B + 325. The derivative thermogravimetry curves of PHB, P(HB–HV), and P(HB–HHx) confirmed only one weight-loss step change. The incorporation of 30 mol % 3-hydroxyvalerate (HV) and 15 mol % 3-hydroxyhexanoate (HHx) components into the polyester increased the various thermal temperatures T_o, T_p, and T_f relative to those of PHB by 3–12°C (measured at B = 40°C/min). DSC measurements showed that the incorporation of HV and HHx decreased the melting temperature relative to that of PHB by 70°C. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 90–98, 2001     

Study on the thermal degradation of epoxidized natural rubber

The thermal degradation and thermooxidative degradation of epoxidized natural rubber (ENR) were studied by thermogravimetry (TG). In the thermal degradation of ENR, the initial temperature of weight loss T₀ = 1.20B + 348, the temperature of maximum weight loss rate T_p = 1.07B + 392, and the final temperature of weight loss T_f = 0.77B + 445. The C_p, which corresponds to the degradation rate at temperature T_p, increases along with the heating rate B and its mean value is 43%, but C_f, which corresponds to the degradation rate at temperature T_f, is not affected by the heating rate, and its average value is close to 100%. As in the thermooxidative degradation, T₀ = 1.84B + 246, T_p = 0.30B + 378, and T_f = 2.27B + 584. The value of C_p increases along with the heating rate B and its mean value is 36%, but C_f is not affected by the heating rate and the average value approximately equals 100%. The thermal degradation in nitrogen could be a one-step reaction, whereas the thermooxidative degradation has a multiple-step reaction. The reactive environment has a great effect on the thermal degradation of ENR and the difference of the mechanisms of the two reaction systems is obvious. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:2207–2211, 1998     

Thermogravimetric analysis of poly(3‐hydroxybutyrate) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)

The thermal degradation of poly(3‐hydroxybutyrate) (PHB) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) [P(HB‐HV)] was studied using thermogravimetry (TG). In the thermal degradation of PHB, the temperature at the onset of weight loss (T_o) was derived by T_o = 0.97B + 259, where B represents the heating rate (°C/min). The temperature at which the weight loss rate was maximum (T_p) was T_p = 1.07B + 273, and the final temperature (T_f) at which degradation was completed was T_f = 1.10B + 280. The percentage of the weight loss at temperature T_p (C_p) was 69 ± 1% whereas the percentage of the weight loss at temperature T_f (C_f) was 96 ± 1%. In the thermal degradation of P(HB‐HV) (7:3), T_o = 0.98B + 262, T_p = 1.00B + 278, and T_f = 1.12B + 285. The values of C_p and C_f were 62 ± 7 and 93 ± 1%, respectively. The derivative thermogravimetric (DTG) curves of PHB confirmed only one weight loss step change because the polymer mainly consisted of the HB monomer only. The DTG curves of P(HB‐HV), however, suggested multiple weight loss step changes; this was probably due to the different evaporation rates of the two monomers. The incorporation of 10 and 30 mol % of the HV component into the polyester increased the various thermal temperatures (T_o, T_p, andT_f) by 7–12°C (measured at B = 20°C/min). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2237–2244, 2001     

Effect of cupric ion on thermal degradation of chitosan

The thermal degradation of chitosan and chitosan–cupric ion compounds in nitrogen was studied by thermogravimetry analysis and differential thermal analysis (DTA) in the temperature range 30–600°C. The effect of cupric ion on the thermal degradation behaviors of chitosan was discussed. Fourier transform-infrared (FTIR) and X-ray diffractogram (XRD) analysis were utilized to determine the micro-structure of chitosan–cupric ion compounds. The results show that FTIR absorbance bands of  N H,  C N ,  C O C etc. groups of chitosan are shifted, and XRD peaks of chitosan located at 11.3, 17.8, and 22.8° are gradually absent with increasing weight fraction of cupric ion mixed in chitosan, which show that there are coordinating bonds between chitosan and cupric ion. The results of thermal analysis indicate that the thermal degradation of chitosan and chitosan–cupric ion compounds in nitrogen is a two-stage reaction. The first stage is the deacetylation of the main chain and the cleavage of glycosidic linkages of chitosan, and the second stage is the thermal destruction of pyranose ring of chitosan and the decomposition of residual carbon, in which both are exothermic. The effect of cupric ion on the thermal degradation of chitosan is significant. In the thermal degradation of chitosan–cupric ion compounds, the temperature of initial weight loss (T_st), the temperature of maximal weight loss rate (T_max), that is, the peak temperature on the DTG curve, and the peak temperature (T_p) on the DTA curve decrease, and the reaction activation energy (E_a) varies with increasing weight fraction of cupric ion. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of atmosphere on the thermal decomposition of chlorinated natural rubber from latex

The kinetics of the thermal decompositions of chlorinated natural rubber (CNR) from latex under both air and nitrogen atmospheres were studied with thermogravimetric analysis (TGA). The thermooxidative decomposition of CNR had two weight-loss step changes in the TGA curves, which occurred at the two distinct temperature ranges of about 160–390 and 390–850°C, respectively. The gaseous products of the first step change were mainly HCl with a little CO₂, and the apparent reaction order (n) was 1.1. The reaction activation energy (E) increased linearly with the increment of heating rate (B), and the apparent activation energy (E₀), calculated by extrapolation back to zero B, was 101.7 kJ/mol. Bs ranging from 5 to 30°C/min were used. The initial temperature of weight loss (T₀) was 1.31B + 252°C, where B is in degrees Celsius per minute. The final temperature of weight loss (T_f) was 0.93B + 310°C, and the temperature of maximum weight-loss rate (T_p) was 1.03B + 287°C. The decomposition weight-loss percentage at T_p (C_p) and that at T_f (C_f) were not affected by B, and the average values were 38 and 60%, respectively. The second weight-loss step change was an oxidative decomposition of the molecular main chain. The value of n was 1.1. E increased linearly with the increment of B, and E₀ was 125.0 kJ/mol. C_f after the second step approached 100%, which indicated complete decomposition. The thermal decomposition of CNR in a N₂ atmosphere had only one weight-loss step change with an n of 1.1. E increased linearly with the increment of B, and E₀ was 98.6 kJ/mol. T₀ was 1.25B + 251°C, T_f was 0.91B + 315°C, and T_p was 1.09B + 286°C. C_p and C_f were not affected by B, and the average values were 37 and 68%, respectively. The weight percentage of more stable, nonthermal decomposed residue was about 30%. The thermal decompositions of CNR in both atmospheres were similar, mainly by dehydrochlorination, at the low temperature range (160–390°C) but were different at the high temperature range (390–850°C). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2590–2598, 2001     

Thermal degradation of poly(3‐hydroxybutyrate) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) as studied by TG,TG–FTIR,and Py–GC/MS

The thermal degradation kinetics of poly(3‐hydroxybutyrate) (PHB) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) [poly(HB–HV)] under nitrogen was studied by thermogravimetry (TG). The results show that the thermal degradation temperatures (T_o, T_p, and T_f) increased with an increasing heating rate (B). Poly(HB–HV) was thermally more stable than PHB because its thermal degradation temperatures, T_o(0), T_p(0), and T_f(0)—determined by extrapolation to B = 0°C/min—increased by 13°C–15°C over those of PHB. The thermal degradation mechanism of PHB and poly(HB–HV) under nitrogen were investigated with TG–FTIR and Py–GC/MS. The results show that the degradation products of PHB are mainly propene, 2‐butenoic acid, propenyl‐2‐butenoate and butyric‐2‐butenoate; whereas, those of poly(HB–HV) are mainly propene, 2‐butenoic acid, 2‐pentenoic acid, propenyl‐2‐butenoate, propenyl‐2‐pentenoate, butyric‐2‐butenoate, pentanoic‐2‐pentenoate, and CO₂. The degradation is probably initiated from the chain scission of the ester linkage. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1530–1536, 2003     

Chitosan and N‐carboxymethylchitosan: I. The role of N‐carboxymethylation of chitosan in the thermal stability and dynamic mechanical properties of its films

Chitosan (degree of deacetylation of 90.2%) and N‐carboxymethylchitosan (N‐CMCh) (degree of substitution of 18.5%) were analyzed using thermogravimetric analysis in order to determine their thermal stability. Also, their films were evaluated using scanning electron microscopy (SEM) and mechanical and dynamic mechanical analysis (DMA). Both polymers showed a thermal degradation peak at T_m ～ 250 °C, with T_onset and weight loss of 175 °C and 62% and 190 °C and 35% for chitosan and N‐CMCh, respectively. N‐CMCh showed a second thermal degradation peak at T_m = 600 °C, with an additional weight loss of 25%. Kinetic thermal analysis showed a slower process of degradation at 100 °C for N‐CMCh compared with chitosan, and an activation energy 13 times higher for the former, confirming the higher stability of N‐CMCh. Analysis of chitosan and N‐CMCh films showed that the latter support a high tension, with lower elasticity, and, as revealed by DMA, N‐CMCh has a more compact film structure, with a crossing arrangement of N‐CMCh fibers, as compared with the chitosan films which were determined from SEM analysis to have fibers in one direction only. Copyright © 2006 Society of Chemical Industry     

Effect of preparation methods on thermal properties of poly(acrylic acid)/silica composites

Poly(acrylic acid)-silica composites have been prepared by two different methods and thermally characterized. The glass transition temperature (T_g) of the PAA-SiO₂ system prepared by mixture method was found to be 120°C irrespective of the type and amounts of silica involved in this work. However, the T_g varied between 132°C and 113°C in the systems prepared by polymerization reaction depending upon the type of silica and percentage conversion. The composites prepared by mixture and polymerization method have been investigated by using thermogravimetry (TGA) to follow the kinetics of anhydride formation and thermal degradation reactions. The activation energy of thermal anhydride formation and thermal degradation reaction was not found to change very much with ratio of PAA-SiO₂ when the composites were prepared by simple mixing. For the composites prepared by polymerization method the activation energy of anhydride formation and thermal degradation reaction were observed to change with percentage conversion. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 891–895, 1998     

The effect of preparation methods on the thermal properties of poly(acrylic acid) / alumina composites

Poly(acrylic acid) - alumina composites have been prepared by two different methods and thermally characterized. The glass transition temperatures (T_g) of the PAA/Al₂O₃ systems prepared by mixture and polymerization method were found to be 126°C and 130°C, respectively, irrespective of the alumina amounts involved in this work. The composites prepared by mixture and polymerization method have been investigated by using thermogravimetry (TGA) to follow the kinetics of anhyride formation and thermal degradation reactions. The activation energy of thermal anhydride formation and thermal degradation reaction was not found to change very much with the ratio of PAA/Al₂O₃ when the composites were prepared by simple mixing. For the composites prepared by the polymerization method, the activation energy of anhyride formation and thermal degradation reaction were observed to change with percentage conversion.     

Thermal degradation of polymethacrylic ester containing bisphenol-S

Thermal degradation of polymethacrylic ester containing bisphenol-S, poly(BPS-M), was investigated under nitrogen and air atmosphere at various heating rates. Ozawa's method was used to calculate the kinetic parameters, activation energy, preexponential factor and reaction order. Thermodegradation of the polymer occurs in one or two stages in nitrogen and air, respectively. The temperature at the start of intense degradation (T_start) and the temperature corresponding to a 50% mass loss (T_50%) were found to be 300 and 402°C, respectively, at a heating rate of 10°C min^?1 in nitrogen. Larger sample masses have a larger temperature interval (ΔT) and a greater mass loss (ΔW). The kinetic order of degradation is unity both in nitrogen and air. The direct pyrolysis mass spectrum of the polymer shows one degradation peak. The most important degradation process under inert atmosphere is the loss of carbon dioxide, phenol and sulphur dioxide. A possible mechanism for thermal decomposition of poly(BPS-M) is proposed based on the product analyses.     

Study on hot air aging and thermooxidative degradation of peroxide prevulcanized natural rubber latex film

The air‐aging process at 120°C and the thermooxidative degradation of peroxide prevulcanized natural rubber latex (PPVL) film were studied with FTIR and thermal gravity (TG) and differential thermal gravity (DTG) analysis, respectively. The result of FTIR shows that the ? OH and ? COOH absorption of the rubber molecules at IR spectrum 3600–3200 cm^?1, the ? C?O absorption at 1708 cm^?1, and the ? C? OH absorption of alcohol at 1105 and 1060 cm^?1 increased continuously with extension of the aging time, but the ? CH₃ absorption of saturated hydrocarbon at 2966 and 2868 cm^?1, the ? CH₃ absorption at 1447 and 1378 cm^?1, and the C?C absorption at 835 cm^?1 decreased gradually. The result of TG‐DTG shows that the thermal degradation reaction of PPVL film in air atmosphere is a two‐stage reaction. The reaction order (n) of the first stage of thermooxidation reaction is 1.5; the activation energy of reaction (E) increases linearly with the increment of the heating rate, and the apparent activation energy (E₀) is 191.6 kJ mol^?1. The temperature at 5% weight loss (T_0.05), the temperature at maximum rate of weight loss (T_p), and the temperature at final weight loss (T_f) in the first stage of degradation reaction move toward the high temperature side as the heating rate quickened. The weight loss rate increases significantly with increment of heating rate; the correlation between the weight loss rate (α_p) of DTG peak and the heating rate is not obvious. The weight loss rate in the first stage (α_f1) rises as the heating rate increases. The final weight loss rate in second stage (α_f2) has no reference to heating rate; the weight loss rate of the rubber film is 99.9% at that time. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3196–3200, 2004     

Organic–inorganic hybrid boron‐containing phenol–formaldehyde resin/SiO2 nanocomposites

The organic–inorganic hybrid boron‐containing phenol–formaldehyde (BPFR) resin/SiO₂ nanocomposites was synthesized in‐situ from boric acid, phenol, and tetramethoxysilane. The structure of BPFR modified and the distributions of silicon element were studied by Fourier‐transform infrared spectroscopy, energy dispersive X‐ray spectrometry, and transmission electron microscope, respectively. The glass transition temperature (T_g) was determined by torsional braid analysis. The results show that silicon element distribution is homogeneous, and the size of nanosilica is about 40–60 nm. The thermal stability and kinetics parameters of thermal degradation were determined by thermogravimetry analysis (TGA). TGA results show that the resin modified has higher heat resistance property when the additive quantity of SiO₂ was 3 wt%. The temperature of 5% weight loss is 487.7°C, which is 12.4°C higher than that of common BPFR. The residual ratio of 3 wt% SiO₂/BPFR was 62.3% at the temperature of 900°C, which is 11.2% higher than that of common BPFR. The mechanics loss peak T_p of 3% SiO₂/BPFR is 33°C higher than common BPFR. Fiberglass‐reinforced BPFR modified by 3 wt% SiO₂ has better mechanical and dielectric properties than that of common BPFR. POLYM. COMPOS., 2008. © 2007 Society of Plastics Engineers     

A study on thermal behavior of a poly(VDF‐CTFE) copolymers binder for high energy materials

This article describes a study on thermal behavior of poly(vinylidene fluoride‐chlorotrifluoroetheylene) [poly(VDF‐CTFE)] copolymers as polymeric binders of specific interest for high energy materials (HEMs) composites by thermal analytical techniques. The non‐isothermal thermogravimetry (TG) for poly (VDF‐CTFE) copolymers was recorded in air and N₂ atmospheres. The results of TG thermograms show that poly(VDF‐CTFE) copolymers get degrade at lower temperature when in air than in N₂ atmosphere. In the derivative curve, there was single maximum degradation peak (T_max) indicating one‐stage degradation of poly(VDF‐CTFE) copolymers for all the samples. The other thermal properties such as glass transition temperature (T_g) and degradation temperature (T_d) for poly(VDF‐CTFE) copolymers were measured by employing differential scanning calorimeter (DSC) technique. The kinetic parameters related to thermal degradation of poly(VDF‐CTFE) copolymers were investigated through non‐isothermal Kissinger kinetic method using DSC method. The activation energies for thermal degradation of poly(VDF‐CTFE) copolymers were found in a range of 218–278 kJ/mol. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

High-temperature degradation of reinforced phenolic insulator

The thermal degradation of graphite and glass-reinforced phenolic insulators have been studied at high temperature by using thermogravimetry analysis (TGA) and Differential Scanning Calorimetry (DSC) analysis. TGA was carried out in a stream of pure nitrogen over temperature range ambient to 900°C and DSC analysis to 500°C. A heating rate of 10°C/min was used for the determination of degradation temperature and heating rates of 5, 10, 20, 30, and 50°C/min were used for the estimation of degradation temperature (T_max) of the insulator at high temperature service and calculation of activation. Activation energy of phenolic resin was calculated as 356 kJ mol⁻¹ using the Ozawa method. T_max was determined as 661°C for 20% conversion. The specific heat capacity of graphite phenolic was found as 970 J kg⁻¹ K⁻¹ at 100°C. The half-life of the phenolic resin was determined to be approximately 116.2 s at 3500°C. The thermal analysis has been conducted using transient heat conduction and the in-depth temperature distribution was evaluated along the rocket nozzle. The better insulator thickness, including the safety factor for graphite and E-glass-reinforced phenolics, were calculated as 3 and 2 mm, respectively. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1877–1883, 1998     

Thermal degradation of cellulose and cellulose esters

Cellulose, cellulose diacetate (CDA), cellulose triacetate (CTA), cellulose nitrate (CN), and cellulose phosphate (CP) were subjected to dynamic thermogravimetry in nitrogen and air. The thermostability of the cellulose and its esters was estimated, taking into account the values of initial thermal degradation temperature T_d, the temperature at the maximum degradation rate T_dm, and char yield at 400°C. The results show that these polymers may be arranged in the following order of increasing thermostability: CN < CP < regenerated cellulose < filter cotton < CDA < CTA. The activation energy (E), order (n), and frequency factor (Z) of their degradation reactions were obtained following the Friedman, Chang, Coats–Redfern, Freeman–Carroll, and Kissinger methods. The dependence of T_d, T_dm, E, n, Ln Z, and char yield at 400°C on molecular weight and test atmosphere is also discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:293–304, 1998     

Characterization of PVC cable insulation materials and products obtained after removal of additives

Organic solvents cyclohexane, dichloromethane, hexane, and tetrahydrofuran were tested to separate the dioctylphthalate (DOP) as plasticizer from the poly(vinyl chloride) (PVC)‐based materials. It was found that the efficiency of ultrasound‐enhanced hexane extraction of the DOP from PVC is 70% and the efficiency of the separation of the DOP and other compounds from the PVC by dissolution in THF followed by subsequent precipitation was 98–99%. Differential scanning calorimetry (DSC) and thermogravimetry (TG) were used to characterize the thermal behavior of PVC materials before and after extraction of plasticizers. It was found that during heating in the range 20–800°C the total mass loss measured for the nontreated, extracted, and precipitated PVC samples was 71.6, 66.6, and 97%, respectively. In the temperature range 200–340°C, the release of DOP, HCl, and CO₂ was observed by simultaneous thermogravimetry (TG)/FTIR. The effect of plasticizers on thermal behavior of PVC‐based insulation material was characterized by DSC in the range ?40–140°C. It was found that, concerning the PVC cable insulation material before treatment, the value of the glass transition temperature (T_g) was 1.4°C, whereas for the PVC sample extracted by hexane, the value of T_g was 39.5°C and for the PVC dissolved in THF and subsequently precipitated, the value of T_g was 80.4°C. Moreover, the PVC samples after extraction of plasticizers, fillers, and other agents were tested to characterize their thermal degradation. The TG and FTIR results of chemically nontreated, extracted, and precipitated samples were compared. The release of DOP, HCl, CO₂, and benzene was studied during thermal degradation of the samples by FTIR. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 788–795, 2006     

Dielectric relaxations in poly [2,2-propane-bis-(4-phenyl thiocarbonate)]

The dielectric relaxation properties of poly[2,2-propane-bis-(4-phenyl thiocarbonate)] (PTC) have been studied. The existence of crystallinity, which can be eliminated by quenching, is detected. The degree of crystallinity of polymer samples was determined by differential scanning calorimetry in order to investigate the effect of this factor on the dielectric behaviour of this polymer. The thermal degradation of the samples was studied by thermogravimetry. The degradation of the polymer begins before the glass transition temperature T_g. The dielectric spectrum is complex showing several relaxation phenomena. With increasing temperature a γ relaxation can be observed at - 100°C (5 kHz). The activation energy obtained from an Arrhenius plot (lnfvs T^?1) is 6 kcal mol^?1. At 160°C the α relaxation which is associated with the glass transition temperature T_g is detected. The dielectric behaviour of this poly(thiocarbonate) is compared with the corresponding poly(carbonate).     

Thermally stimulated depolarization current studies on PC/PTBF blends

Thermally stimulated depolarization current (TSDC) studies have been carried out on blends of polycarbonate (PC) and poly(p-t-butyl phenolformaldehyde) (PTBF) using electric poling at temperatures ranging from 348°K to 383°K. The PC/PTBF blends poled at identical electric field (E_p) and temperature (T_p) exhibit a continuous distribution of polarizability (in general, in the range 300°K to 450°K) with a blend composition dependent single peak (T_M). With increasing E_p and T_p, the TSDC peak of a blend shifts toward higher temperature with increasing peak current (I_M) and charge (Q) associated with the peak. The effects of polarization field and temperature indicate that the polarization in the blend system is due to induced dipole formation. The activation energy decreases with increasing PTBF content in the blend, indicating shallow traps in PC/PTBF electret. The present blend electrets, however, comparative to its two components PC and PTBF, store more charge but decay faster. © 1994 John Wiley & Sons, Inc.