Preparation and thermal degradation kinetics of terpolymer poly(?-caprolactone-co-1,2-butylene carbonate)

Poly(?-caprolactone-co-1,2-butylene carbonate) (PBCCL) was successfully synthesized via terpolymerization of carbon dioxide, 1,2-butylene oxide(BO) and ?-caprolactone (CL). A polymer-supported bimetallic complex (PBM) was used as catalyst. The influences of various reaction conditions such as reaction content, reaction time and reaction temperature on properties of terpolymers were investigated. When CL content increased, the viscosity-average molecular weights (M_v), glass transition temperature (T_g) and decomposition temperature (T_d) of PBCCL improved relative to those of poly(1,2-butylene carbonate) (PBC). Prolonging the reaction time resulted in increase in M_v and T_g. As reaction temperature increased, the molar fractions of CL (fCL) increased obviously. When the reaction temperature went beyond 80 °C, the resulting copolymers tended to be crystalline. The thermal properties and degradation behaviors of PBCCL were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The apparent activation energy and thermal degradation model of PBCCL was estimated by means of Ozawa-Flynn-Wall method and Phadnis-Deshpande method, respectively. The results showed that T_g and T_d of the terpolymer PBCCL were much higher than those of PBC. The thermal degradation behavior of PBCCL was evidenced by one-step thermal degradation profile. The average apparent activation energy is 77.06 kJ/mol, the thermal degradation kinetics follows the power law thermal decomposition model.     

Preparation of nano poly(phenylsilsesquioxane) spheres and the influence of nano-PPSQ on the thermal stability of poly(methyl methacrylate)

The nano poly(phenylsilsesquioxane) spheres (nano-PPSQ) were prepared by the sol?Cgel method and incorporated into poly(methyl methacrylate) (PMMA) by in situ bulk polymerization of methyl methacrylate. The structure of nano-PPSQ was confirmed by transmission electron microscope and thermogravimetry analysis (TG). The interaction between nano-PPSQ and PMMA was investigated by Fourier transform infrared spectra (FT-IR). The influence of nano-PPSQ on the thermal stability of PMMA was investigated by TG and differential scanning calorimetry (DSC) measurements. The results indicated that nano-PPSQ enhanced the thermal stability and the temperatures of glass transition (T _g) of nanocomposites. The effect of the heating rate in dynamic measurements (5?C30?°C?min^?1) on kinetic parameters such as activation energy by TG both in nitrogen and air was investigated. The Kissinger method was used to determine the apparent activation energy for the degradation of pure PMMA and nanocomposites. The kinetic results showed that the apparent activation energy for degradation of nanocomposites was higher than that of pure PMMA under air.     

Investigations and molecular modeling of some thermophysical properties of polysulfones

Degradation of commercial polysulfones (PSF) was investigated in air and in inert atmosphere (nitrogen) using thermogravimetric (TG) method. It has been found that the degradation of Udel P-1800 PSF is initiated about 400°C, both in air and in nitrogen. The activation energy of degradation of PSF, (E _a), has been calculated by the Kissinger and Ozawa methods. The value ofE _a about 200 kJ·mol^?1 has been found for both air and nitrogen atmosphere. Experimental results concerning thermal properties of PSF (T _g andT _d,1/2) were compared with those obtained by the computer modeling technique, and a good agreement has been found.     

Study on the PMMA/GO nanocomposites with good thermal stability prepared by in situ Pickering emulsion polymerization

Graphene oxide (GO) is used as a stabilizer in the Pickering emulsion polymerization of methyl methacrylate (MMA) to prepare PMMA/GO nanocomposites. Transmission electron microscope studies of the emulsion polymerization products showed that the average diameter of nanocomposite particles was about 150 nm, the transparent GO flakes covered the surface of the particles, and were well dispersed in polymer matrix. The influence of GO on the thermal stability of PMMA was investigated by thermogravimetry analysis and differential scanning calorimetry. The results showed that the thermal stability and the glass transition temperature (T _g) of PMMA/GO nanocomposites were improved obviously compared with PMMA. The apparent activation energy (E _a) for the degradation process of PMMA/GO nanocomposites was evaluated by Kissinger method, which indicated that their E _a s were much higher than those of PMMA both in nitrogen and air atmosphere.     

Kinetic study of the thermal and thermo-oxidative degradations of polylactide-modified films for food packaging

In this study, the thermal degradations of some commercial polylactide (PLA) films, pure and subjected to various superficial treatments, were investigated in both inert (flowing nitrogen) and oxidative (static air) atmospheres. Degradations were carried out in a thermobalance, in the scanning mode, at various heating rates, and the obtained thermogravimetric curves were discussed and interpreted. Experiments, performed in the temperature range of 35–700 °C, showed similar behavior in both the atmospheres used. The initial decomposition temperature (T _i) and the apparent activation energy (E _a) of degradation of the differently treated PLA films were determined and compared with each other and with those of untreated PLA. The E _a of degradation was obtained by Kissinger’s method, and the values were found increased linearly as a function of crystallinity percentage (%c) as well as the T _i values. The glass transition temperature (T _g) was also determined by differential scanning calorimetry. All the investigated parameters showed dependence on different treatments made to the films. The results obtained for the degradations of PLA films were compared with each other, and a classification of thermal stability in the studied environments were made.     

Gel permeation chromatography studies of chain scission and cross-linking during photo-oxidation of atactic polystyrene below and at tg

Photo-oxidative degradation of polystyrene in the form of film 20 μm thick was carried out in air using u.v. light of 254 nm at room temperature and at temperatures up to T_g. GPC was used to study changes of molecular weight distribution during the process. The GPC results were analysed using equations for an initially most probable distribution and non-uniform energy dissipation; the quantum yield values of chain scission and cross-linking of polystyrene during degradation were calculated. Initially, degradation progressed at high rate, connected with consumption of oxygen dissolved in the film. The slower subsequent degradation was connected with consumption of oxygen supplied during the reaction. An appreciable increase in the quantum yields for chain scission and cross-linking was observed just below and at T_g for the initial stage of photo-oxidative degradation. This increase of the quantum yield of photodegradation was caused by increased mobility of oxygen molecules in the film, connected with movement of polymer chain elements.     

Influence of thermal treatment on the glass transition temperature of thermosetting epoxy laminate

The influence of accelerated thermal treatment of thermosetting epoxy laminate on its glass transition temperature was studied. Lamplex^® FR-4 glass fibre-reinforced epoxy laminate (used for printed circuit board manufacturing) was used in these experiments. The composite was exposed to thermal treatments at temperatures ranging from 170 °C to 200 °C for times ranging from 10 to 480 h. The glass transition temperature (T_g) was analysed via dynamic mechanical analysis (DMA). It has been proven that the glass transition temperature rapidly decreases in reaction to thermal stress. The obtained T_g data were used for Arrhenius plots for different critical temperatures (T_g-crit. = 105–120 °C). From their slopes (?E_a/R), the activation energy of the thermal degradation process was calculated as 75.5 kJ/mol. In addition to this main relaxation mechanism, DMA also recorded one smaller relaxation process in the most aged samples. Microscopic analysis of the sample structure showed the presence of pronounced small regions of degradation both on the surface and in the inner structure, which are probably the causes of microscopic delamination and the smaller relaxation process.     

Nucleation and crystal growth in Na2O · 2 CaO · 3 SiO2 glass: a DTA study

The non-isothermal devitrification of Na₂O · 2 CaO · 3 SiO₂ glass has been studied by differential thermal analysis in order to evaluate, from DTA curves, the temperature of maximum nucleation rate, T_m, and the activation energy values, E_c, for crystal growth.The temperature, T_m=580°C, is very close to the glass transition temperature, T_g=570°C, and the value of E_c=78 Kcal mole^?1 for the surface crystal growth is nearly the same as the value E_c=89 kcal mole^?1 for the bulk crystal growth; both are consistent with the activation energy for viscous flow. It is also pointed out that the nucleation rate—temperature curve and the crystallization rate—temperature curve are partially overlapped.     

Silver sulfide/poly(3-hydroxybutyrate) nanocomposites: Thermal stability and kinetic analysis of thermal degradation

The non-isothermal degradation of poly(3-hydroxybutyrate) (PHB) and silver sulfide/poly(3-hydroxybutyrate) (Ag₂S/PHB) nanocomposites was investigated using thermogravimetric (TG) analysis. In the composite materials, Ag₂S caused the degradation of PHB at a lower temperature as opposed to that of neat PHB. Moreover, an increase Ag₂S loading in the PHB decreased the onset temperature (T_onset) of thermal degradation, whereas it was raised upon augmenting the heating rate. From Kissinger plots, the observed trend of the degradation activation energy, E_d, was attributed to polymer-particle surface interactions and the agglomeration of Ag₂S. The thermal degradation rate constant, k, was linearly related to the Ag₂S loading in PHB. Thus, the Ag₂S nanoparticles effectively catalyzed the thermal degradation of PHB in the Ag₂S/PHB nanocomposites. Differential scanning calorimetry (DSC) data also supported the catalytic property of Ag₂S.     

Non-equilibrium self-assembled structures in thick PS-b-PMMA copolymer films

Phenomena associated with the order-disorder transition (ODT) of block copolymers have been studied by optical light microscopy, SAXS, SEM, TEM and DSC. Observations have been made on almost symmetric polystyrene-block-poly(methyl methacrylate) samples of three molecular weights and their mixture. We observed non-equilibrium supermolecular structures several microns in diameter in the bulk of thick PS-b-PMMA films (ca. 100 μm thickness) prepared by vacuum drying of films cast from a non-selective solvent (after a short-term annealing above the T_g). Apparent LDOT (lower disorder-to-order transition) behaviour is observed for samples with non-equilibrium morphology surviving from solution as deduced from SAXS 1/I_m vs 1/T and the full width at half-maximum vs 1/T plots.The measurements point to complex behaviour near the ODT, but homogenization of samples upon long-term annealing well above the T_g temperature call into existence common stacks of lamellae observable in SEM images of microphase-separated samples. This verifies the opinion that the observed apparent LDOT behaviour of samples II, III and II + III is associated with the frozen non-equilibrium morphology surviving from solution. This is confirmed by SAXS measurement on a homogenized sample displaying the expected UDOT behaviour. It has been demonstrated that self-assembled structures prepared by vacuum drying of films cast from a non-selective solvent are non-equilibrium structures and their successive ordering is difficult due to a relative narrow temperature interval between T_g and degradation temperature. The conditions under which BCP films are prepared thus have a pronounced effect on the microstructure and microphase ordering process.     

Sol–gel synthesis and enhanced properties of a novel transparent PMMA based organic–inorganic hybrid containing phosphorus,nitrogen and silicon

A novel flame-retardant silane containing phosphorus and nitrogen, tetramethyl(3-(triethoxysilyl)propylazanediyl) bis(methylene) diphosphonate (TMSAP), is firstly synthesized and then incorporated into poly(methyl methacrylate) (PMMA) matrix through sol–gel method to produce organic–inorganic hybrids. The chemical structure of TMSAP was confirmed by Fourier transform infrared spectra, ¹H nuclear magnetic resonance (NMR) and ³¹P NMR spectra. The hybrids obtained maintain relatively high transparency, and exhibit a significant improvement in thermal properties, mechanical performance and flame retardancy when compared to pure PMMA, including increased glass transition temperature (T _g ) by 11.4 °C, increased onset thermal degradation temperature (T_0.1) by 82.6 °C, increased half thermal degradation temperature (T_0.5) by 42.0 °C, increased hardness, increased limited oxygen index and decreased heat release rate. Morphological studies of hybrids by scanning electron microscopy (SEM) and ²⁹Si MAS NMR suggest that cross-linked silica network is formed in the hybrids and the inorganic silica particles are distributed well in the polymer matrix. Thermal degradation behaviors investigated by thermogravimetric analysis and char structure analysis studied by SEM and X-ray photoelectron spectroscopy demonstrate the catalytic charring function of TMSAP, and synergistic effect between phosphorus, nitrogen and silicon element. The formation of network structure, homogeneous distribution of silica and the char formation during degradation play key roles in these property enhancements. Detailed mechanisms for these enhancements are proposed.     

The influence of sulfonation degree on the thermal behaviour of sulfonated poly(arylene ethersulfone)s

Initial decomposition temperature (T_i), apparent activation energy of degradation (E_a) and glass transition temperature (T_g) of some low molar mass (M_n ≈ 8000 g mol⁻¹) sulfonated poly(arylene ethersulfone)s s-(PAES)s were determined to check their dependence on sulfonation degree (SD). The results obtained were compared with those for unsulfonated poly(arylene ethersulfone) PAES. In order to have an accurate control of the chemical structure, a pre-sulfonation route was followed for the preparation of sulfonated compounds. The thermal behaviour of the investigated s-(PAES)s as well as that of PAES appears not to be influenced by the environment (flowing nitrogen or static air atmosphere) of degradation. Both T_i and T_g values of s-(PAES)s were higher than those of PAES and increased quite linearly as a function of sulfonation degree. An analogous linear trend was observed for the apparent degradation energy of s-(PAES)s, but the values found were largely lower than those of unsulfonated homopolymer. The results are discussed and interpreted.     

Preparation and Study of Epoxidized Natural Rubber

Epoxidized natural rubbers (ENRs) with different extents of epoxidation (B) were prepared under various reaction conditions. The effects of the amount of H₂O₂ and the reaction time on B are discussed. The glass transition temperature T_g, the thermal degradation temperature and the activation energy of thermal degradation of the ENRs increase with B. The results indicate that the thermal stability of the ENRs increases with B.This revised version was published online in November 2005 with corrections to the Cover Date.     

New coil geometries for the study of secondary discharge in atmospheric-pressure helium inductively coupled plasma mass spectrometry

Several coil geometries are proposed to reduce the secondary discharge in atmospheric-pressure helium inductively coupled plasma mass spectrometry (He ICPMS) using a crystal-controlled 40-MHz generator. The effectiveness of the proposed geometries in controlling the plasma potential is investigated by the Langmuir probe method and ion kinetic energy (IKE) measurements. The influence of RF power on plasma gas temperature (T_g) is investigated through measurements of ICP-mass spectrometer interface pressure and IKEs for new and conventional coil geometries. Trends in plasma potential and T_g are well correlated, revealing that T_g is elevated (to ∼3500 K) at high power levels mainly as a consequence of the interaction between the ICP and the grounded sampler. The reduction of the secondary discharge results in lower T_g values (∼2600 K), necessitating the use of a membrane desolvator to remove water-related polyatomic interferences observed in the mass spectrum. Solvent removal also improves the sensitivity for bromine as a high-ionization-potential element by one order of magnitude compared to the previous studies.     

Comparison of electrical conductivity and thermal properties of borosilicate glass with and without simulated radioactive waste

Electrical conductivity and percentage linear thermal expansion of the borosilicate glass (BSG) and simulated waste-loaded borosilicate glass (BSGW) were measured in the temperature range of 300–780 K and compared. Pronounced increase in electrical conductivity was observed around glass transition temperature (T _g) of BSG and BSGW. The activation energy (E _a) of electrical conduction determined from the measured data for BSG and BSGW is 0.961 ± 0.005 and 0.960 ± 0.005 eV, respectively. The % average linear thermal expansion of BSGW showed a slight decreasing trend compared with pristine BSG. The average coefficient of thermal expansion determined from dilatometry data is 12.87 ± 0.24 × 10^?6 and 11.94 ± 0.23 × 10^?6 K^?1 for BSG and BSGW, respectively. The T _g measured by dilatometry is 806 ± 24 K for BSG and 790 ± 23 K for BSGW, respectively. The T _g measured by DTA was found to be 820 ± 7 and 805 ± 5 K for BSG and BSGW, respectively, for heating cycle. The T _g values obtained from DSC measurements are 805 ± 5 and 803 ± 5 K for BSG and BSGW, respectively. The T _g of BSGW showed a slight decrease compared with that of BSG. The values obtained by DSC examination also showed the lowering of T _g values for the waste-loaded composition. The lowering of T _g may be attributed to the interaction of glass-forming agents and simulated waste elements.     

Poly(ether ether ketone)/poly(aryl ether sulphone) blends: thermal degradation behaviour

The thermodegradative behaviour of blends of poly(ether ether ketone) (PEEK) and poly(aryl ether sulphone) (PES) was studied by dynamic thermogravimetry in order to analyze their thermal stability. The Freeman-Carrol differential approach was used to determine the kinetic parameters i.e. the apparent activation energy (E_a) and order of reaction (n), of the degradation process. The results indicate that the presence of one component influences the thermal stability of the other. Both, temperature for 5% weight loss (T₅) and E_a for blends show a negative deviation from the linear behaviour, which signifies a lowering of thermal stability compared to homopolymers. The decrease in the thermal stability at low concentration of PES in PEEK has been explained on the basis of chemical interactions of the degradation products of PES, which has lower induction temperature for degradation, with PEEK and also on the reduction of viscosity of the medium. But the decrease in thermal stability at low concentration of PEEK in PES is unusual and at present, without the complete elucidation of degradation mechanism in these blends, is difficult to explain.     

Reactivity ratios for the oxidative copolymerizations of indene with methyl methacrylate and methacrylonitrile

The copolyperoxides of indene with methyl methacrylate and methacrylonitrile have been synthesized by the free-radical-initiated oxidative copolymerization of indene and the monomers. The compositions of copolyperoxides, obtained from 1H and 13C NMR spectra, have been utilized to determine the reactivity ratios. The reactivity ratios indicate that the copolyperoxides contain a large proportion of the indene units in random placement. Thermal degradation studies of the copolyperoxides by differential scanning calorimetry and electron-impact mass spectroscopy support alternating peroxide units in the copolyperoxide chain. The energy of activation for thermal degradation suggests that the degradation is controlled by the dissociation of the peroxide (-O-O-) bonds in the copolyperoxide chain. The flexibility of copolyperoxide in terms of glass transition temperature (T_g) has also been examined.     

Calorimetric measurement of the maximum glass transition temperature in a thermosetting resin

The measurement of the maximum glass transitionT _g∞ of a thermosetting resin is usually performed by differential scanning calorimetry in the second scan (T _g2scan), after a previous scan by heating up the sample to a temperature where the exothermic curing reaction has been completed. However, this method can eventually produce thermal degradation, decreasing the crosslinking density and theT _g of the sample. Values ofT _g2scan between 95? and 102?C were found in an epoxy resin based on DGEBA cured with phthalic anhydride. Thermal degradation effects can be avoided if the measurement is performed by isothermal curing and further determination ofT _g. AT _g∞ value of 109?C is achieved, which is the maximum value ofT _g according to the topological limit of conversion.     

Effect of pH on the formation and combustion process of sol-gel auto-combustion derived NiZn ferrite/SiO2 composites

A nitrate-citrate-silica gel was prepared from metallic nitrates, citric acid, and silica powder by sol-gel process, and it was further used to synthesize Ni_0.5Zn_0.5Fe₂O₄/5wt% SiO₂ nanocomposites by auto-combustion. The effect of pH on the formation of NiZn ferrite/SiO₂ and thermal properties of gel precursors was studied by XRD, IR, EPR, TGA and DTA techniques. The results revealed that the ratio of the citrate ion to the nitrate ion is directly related to the pH of the solution. The pH in the starting solution affects the combustion process, and then determines the particle size of the as-synthesized powder. The EPR parameters (peak-to-peak linewidth, g factor, and spin number) increased with increasing pH, whereas the spin-spin relaxation time (T₂) decreased. The thermal stability and enthalpy of the decomposition process in air decreased with increasing pH, whereas the enthalpy in nitrogen increased. Moreover, the activation energy (E_a) of thermo-oxidative degradation of the gel precursor at pH 3 was much lower than the gel precursor at pH 5 and 7, and that increased with increasing pH.     

Characterization and degradation of the poly(methylphenylsiloxane)–poly(methyl methacrylate) graft copolymer

Poly(methylphenylsiloxane)–poly(methyl methacrylate) graft copolymers (PSXE-g-PMMA) were prepared by condensation reaction of poly(methylphenylsiloxane)-containing epoxy resin (PSXE) with carboxyl-terminated poly(methyl methacrylate) (PMMA), and they were characterized by gel permeation chromatography (GPC), infrared (IR), and ²⁹Si and ¹³C nuclear magnetic resonance (NMR). The microstructure of the PSXE-g-PMMA graft copolymer was investigated by proton spin–spin relaxation T₂ measurements. The thermal stability and apparent activation energy for thermal degradation of these copolymers were studied by thermogravimetry and compared with unmodified PMMA. The incorporation of poly(methylphenylsiloxane) segments in graft copolymers improved thermal stability of PMMA and enhanced the activation energy for thermal degradation of PMMA. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2521–2530, 1998