Initial Weight Loss Temperature Research Articles

Melt flow properties, mechanical properties, thermal properties and morphology of polycarbonate/highly branched polystyrene blends

AbstractA highly branched polystyrene (HBPS) was synthesized via the copolymerization of 4‐(chloromethyl) styrene with styrene using the self‐condensing atom transfer radical polymerization method. The addition of HBPS as a melt modifier for polycarbonate (PC) was attempted. Melt flow properties, mechanical properties, thermal properties and morphology of the blends were studied. The results showed that a significant drop in the blend viscosity occurs immediately on addition of HBPS. Impact strength, tensile strength and glass transition temperature (Tg) of all the blends have not been significantly reduced compared with those of pure PC. The TGA analyses showed that an initial weight loss temperature of all the blends is above 458 °C and slightly low compared with that of pure PC, but all the blends still have excellent thermal stability. Morphological studies using SEM showed that a two‐phase morphology is characteristic of all the blends, with more or less spherical droplets of the minor HBPS phase dispersed in the continuous PC phase. Copyright © 2006 Society of Chemical Industry

Modification of the halogen end groups of polystyrene prepared by ATRP

The stabilization modification of the halogen end groups of polystyrene prepared by atom transfer radical polymerization (ATRP) has been attempted. The reaction mechanism adopted is radical chain transfer reaction, and iso-propylbenzene is employed as not only the chain transfer agent but also the solvent. Moreover, Cu 0 is used as the acceptor of the transformed halogen atom in some experiments. As evidenced by 1H NMR analysis of the modified products, the halogen end group can really be converted into the much more stable carbon–hydrogen structure. When Cu 0 is not used, the conversion of the halogen end groups rises rapidly during the early stage and the increase rate slows down after about 8 h reaction. In view of the influence of reaction temperature on the modification, the conversion increases almost exponentially with temperature in the range of 80–100 °C, and the increase rate slows down at higher temperature. 1H NMR and SEC analyses prove that the modification reaction does not destroy the polymer backbone and the molecular weights remain almost the same as those of the unmodified samples. When Cu 0 is introduced, the modification reaction proceeds much rapidly, the conversion of the halogen end groups rises almost linearly at the early stage and the nearly complete (>95%) dehalogenation of the polymeric chains is observed after only 12 h reaction. However, the molecular weights rise and the polydispersities become wider after the modification, which implies that the modification is accompanied with the couple termination of the polystyrene radicals besides chain transfer reaction. Furthermore, the couple termination can be restrained at some lower catalyst concentration. Indeed, the modified polymers show improved thermal stability, the initial weight loss temperatures is increased from 196 °C to 378 °C for the linear polystyrene and from 203 °C to 261 °C for the hyperbranched polystyrene.

Studies on the atom transfer radical polymerization of a maleimide AB* monomer and modification of the halogen end groups

The atom transfer radical polymerization (ATRP) of an AB* monomer, N-(4-α-bromobutyryloxy phenyl)maleimide (BBPMI), was conducted using the complex of CuBr/2,2′-bipyridine as catalyst. The study of kinetics of polymerization and the growth behavior of macromolecules show that the polymerization proceeds rapidly in first 1 h and then slows down. The decrease in the rate of polymerization is ascribed to the poor reactivity of maleimide radicals from A* to initiate the polymerization of maleimide double bonds. The molecular weight of the resulting polymer also increases with the dosage of catalyst. The coincidence of molecular weight determined by hydrogen proton nuclear magnetic resonance spectroscopy ( 1H NMR) and gel permeation chromatography (GPC) proves that the resulting polymer is of linear structure, which is further verified by 13C NMR measurement and high performance liquid chromatography (HPLC) analysis of the hydrolysate of the resulting polymer. The stabilization modification of the halogen end groups of the resulting polymer by free-radical chain transfer reaction was attempted under ATRP condition. Isopropyl benzene was employed as the chain transfer agent. Indeed, the modified polymer with carbon–bromine bonds conversion of 40.7% shows enhanced thermal stability. The initial weight loss temperature has been increased from 193 to 243 °C. On the other hand, the atom transfer radical copolymerization of BBPMI with styrene resulted in the formation of hyperbranched polymer.

Studies on the blends of polycarbonate and highly branched polystyrene

AbstractA highly branched polystyrene (HBPS) was synthesized via the copolymerization of 4‐(chloromethyl) styrene with styrene using the self‐condensing atom transfer radical polymerization method. The addition of this highly branched polystyrene as a melt modifier for polycarbonate (PC) was attempted. Indeed, the results show that the addition of highly branched polystyrene can decrease the melt viscosity of PC with little change in mechanical properties, although the blends do exhibit lower thermal stability compared with pure PC. Extrapolation shows that all of the blends have an initial weight loss temperature above 450°C with a statistic heat‐resistant index Ts above 225°C. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2425–2430, 2004

Synthesis and properties of polymers containing aromatic amino groups in the main chain and their glass-forming model compounds

Polymers containing di(carbazol-3-yl)phenylamine and N, N ′-di(carbazol-3-yl)- N, N ′-diphenyl-1,4-phenylenediamine units in the main chain have been synthesized by a modified Ullmann condensation as a key step. The number-average molecular weights of the polymers synthesized were in the range of 2300–4800 with a molecular weight distribution of 1.42–2.25. Well defined model compounds of the title polymers were synthesized by stepwise reactions. All the materials exhibit high thermal stability with the initial weight loss temperatures exceeding 320 °C and form glasses. Their glass transition temperatures range from 102 to 216 °C as characterised by differential scanning calorimetry. The electron photoemission spectra of thin films of the synthesized compounds have been recorded and the ionisation potentials of 5.0–5.1 eV have been established.

Research on Coal Reactivity: Making a Comparison Between Hydrogenation with H-Donor Solvent and Pyrolysis in N2 Atmosphere

The objectives of this study are to seek answers to the following issues: Why are different ways used to analyze coal's reactivity? Could different methods of measuring coal's reactivity be comparable? Is there any relation among them? Two methods, coal hydrogenation and coal pyrolysis, were employed to investigate coal's reactivity. Six kinds of coals from lignite to anthracite were studied. It was found that the activity energy calculated from the thermogravimetry analysis of coal pyrolysis had a limitation; the initial and maximum temperature of weight loss during coal pyrolysis was more relevant to coal reactivity. These two temperatures, and the amount of hydrogen transferred during coal that reacted with the H-donor THN, were comparable. In the mean time, the methodological canonical relation analysis was used theoretically to compare the two kinds of reactivity and has a proof from a mathematic point of view. Results showed that these two kinds of reactivity had similitude.

A thermoanalytical study of the co-pyrolysis of coal-tar pitch and petroleum pitch

Four pitch blends were prepared at laboratory scale by mixing a coal-tar pitch and a petroleum pitch in several proportions (CTP:PP 85:15, 70:30, 55:45 and 40:60). Single pitches and blends were characterized by standard procedures, infrared spectroscopy and size exclusion chromatography. Pyrolysis behaviour and interactions between the two pitches in the blends were studied by thermogravimetric analysis (TG/DTG) and differential scanning calorimetry (DSC). The results show that blending does not alter the composition of pitches. However, the TG/DTG curves reveal that coal-tar pitch and petroleum pitch interact actively during pyrolysis, modifying the temperature of initial weight loss and the temperature of the maximum rate of weight loss. Primary quinoline-insoluble particles present in coal-tar pitch and transferable hydrogen seem to be the main factors responsible for these modifications. The DSC curves show that the presence of coal-tar pitch in the blends reduces the reactivity of the petroleum pitch and shifts the exothermic peaks observed at the temperature of the cracking/polymerization reactions (>400 °C) to lower temperatures.

Pyrolysis behaviour of stabilized self-sintering mesophase

A coal-tar pitch-based mesophase and a naphthalene-based mesophase were stabilized with air, using a multi-step temperature/time program from 200 to 300 °C. The extent of the stabilization was monitored by elemental analysis. The pyrolysis behaviour of the stabilized samples was studied by thermogravimetric analysis and differential scanning calorimetry. The results showed that the different chemical composition of parent mesophases affected the degree and effectiveness of stabilization, and consequently, the plasticity of the stabilized samples and the intensity of the exothermic effects during their pyrolysis. Naphthalene-based mesophase is more aliphatic and oxygen is taken more rapidly and in a larger amount than in coal-tar pitch-based mesophase. Consequently, the naphthalene-based mesophase stabilized more easily but stabilization was more difficult to control. Moreover, the variations in oxygen uptake and weight gain during stabilization reveal that in this sample, above 250 °C, degradation competes with stabilization. The pyrolysis behaviour of the mesophases is extremely sensitive to the changes produced by stabilization. In the coal-tar pitch-based mesophase the weight loss decreased, and the temperature of maximum rate of weight loss and temperature of initial weight loss increased with the severity of stabilization, while in the naphthalene-based mesophase this tendency was not observed. The competition between stabilization and degradation seems to be the responsible factor for this different behaviour. It was also found that the sinterability of the stabilized samples was mainly governed by their plasticity.

Thermogravimetric and FTIR studies of chitosan blends

Results of spectrophotometric and thermogravimetric studies of chitosan (CH) blends with polyvinyl alcohol (PVAL), starch (S) and hydroxypropylcellulose (HPC) obtained by casting from solutions in the form of transparent films containing 0–1.0 weight fraction of CH were discussed. Blends containing S are homogeneous only in the case of low-weight fraction of S (to 0.3). On the basis of results of thermodegradation in dynamic and isothermal conditions, thermal stability of the tested systems was estimated. Thermogravimetric measurements in dynamic conditions were carried out in the temperature range of 100–450 °C at constant heating rate 15 °C/min. From thermogravimetry (TG) and DTG curves the activation energy and characteristic parameters of degradation of the tested blends were determined. The observed growth of activation energy and T p—temperature of initial weight loss, T max—temperature of maximal rate and C e—degree of conversion at the end of the measurement (at temperature 450 °C) along with the increase of polymer fraction (HPC and S) in the CH blend provides an evidence of improved thermal stability of the systems tested. Investigations in isothermal conditions in air at temperature from 100 to 200 °C confirmed appreciable improvement of CH thermal stability in the blends being tested. Infrared spectroscopic analysis of the blends showed a distinct stabilization of the process of chain scission. In the band at 1080 cm −1 associated with absorption in –C–O–C– group during degradation of the blends at temperature 200 °C much smaller decrease due to molecular scission were observed than in the case of pure CH.

Preparation of novel UV-curable methacrylated urethane resins from a modified epoxy resin and isocyanatoethylmethacrylate (IEM)

New UV curable methacrylated urethanes (PAPHEN-XIEM) were synthesized by substituting X percent (e.g., 10, 20, 30 %) of the total OH content of the PAPHEN-301 (Scheme 1) with isocyanatoethyl methacrylate (IEM). These resins were used alone (neat resin formulation) or as a mixture of 5, 10 and 13 % (w/w) respectively with methacrylated urethane prepolymer (PTHFUMA) in UV systems. For neat resin formulations, tensile strength and modulus values were observed to be inversely proportional with the modification degree of PAPHEN-301 as opposed to what is normally expected. This may be explained as a result of screening effect of increasing unsaturation. The water absorption capacities for neat resins and PTHFUMA-included formulations were decreased as the modification degree increased due to the replacement of hydrophilic OH groups of PAPHEN-301 by the hydrophobic methacrylate groups. TGA thermograms of neat resin formulation show that, initial weight loss temperatures are lower; possibly owing to the higher methacrylate content in the formulations.

Thermogravimetric study of phosphated polyurethane ionomers

Segmented polyurethane dispersions containing bound phosphate groups on the soft segment have been synthesised from a phosphate containing macroglycol, a diisocyanate and a chain extender. TGA study of these polymers has revealed three stages of degradation. The initial weight loss temperature for the phosphated polyurethane dispersions was lower than the ones without phosphate indicating that degradation started at the soft segment that contains the phosphate groups. The degradation profile of the dispersions was also dependent on the neutralising base. The higher char yield of phosphated polyurethanes was related to its fire retardant property and could be used as fire retardant coatings.

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

AbstractThe 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 (Tf) was 0.93B + 310°C, and the temperature of maximum weight‐loss rate (Tp) was 1.03B + 287°C. The decomposition weight‐loss percentage at Tp (Cp) and that at Tf (Cf) 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. Cf 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, Tf was 0.91B + 315°C, and Tp was 1.09B + 286°C. Cp and Cf 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

Thermooxidative decomposition and its kinetics on chlorinated natural rubber from latex

AbstractThermooxidative decomposition and its kinetics on chlorinated natural rubber (CNR) from latex are studied by thermal gravimetry (TG) analysis and TG coupled with FTIR spectroscopy. The thermooxidative decomposition of CNR is a two‐step reaction. The first step is the reaction of dehydrochlorination of which the reaction order (n) is 1.1; the reaction activation energy (E) increases linearly with the increment of the heating rate (B), and the apparent activation energy (E0) is 101.7 kJ/mol. The initial temperature of weight loss (T0) is 1.29B + 248.7, the final temperature of weight loss (Tf) is 0.86B + 312.4, and the temperature at the maximum weight loss ratio (Tp) is 1.05B + 286.2. The decomposition ratio at Tp (Cp) is not affected by B, and its average value is 38%. The decomposition ratio at Tf (Cf) is also not affected by B, and its average value is 60%. The second step is an oxidative decomposition reaction of the molecular main chain. The value of n is 1.1, E increases linearly with the increment of B, E0 is 125.0 kJ/mol, the relation between B and T is similar to that of the first step, and Cf approaches 100%. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1305–1309, 2001

Synthesis and Polymerization of Epoxy Methacrylates, 2. Acylated Epoxy Methacrylates and their Copolymers

Partially (20–75%) acylated isopropylidene-bis[1,4-phenyleneoxy(2-hydroxytrimethylene)] dimethacrylate (BisGMA) was prepared by a single step reaction of 2,2-bis[4-(2,3-epoxypropoxy)phenyl]propane (DGEBA) with methacrylic acid (MAA), methacrylic anhydride (MAAn) and/or acetic anhydride catalyzed by 0.8 mol-% N-methylimidazole at 90–100°C. In any case, MAA was substituted by an equimolar quantity of the anhydride. The reaction kinetics of DGEBA with MAA and MAAn follows a first order law up to a conversion of epoxy groups corresponding to the initial molar ratio of MAAn. For different mole fractions xMAA, the reaction rate was found to be directly proportional to x0.5MAA. The viscosity of BisGMA decreased with an increase in the acylation degree. Acylated BisGMA was copolymerized with triethylene glycol dimethacrylate (TEGMA) by use of a redox initiator system at room temperature and with vinyltoluene (VT) initiated by di-tert-butyl peroxide at 150–200°C, respectively, both in the presence of 70–76 wt.-% of quartz filler. Different dependencies of the content of sol and the conversion of C=C double bonds were observed for thermally polymerized composites from VT with acetylated and methacrylated BisGMA, respectively. Methacrylated BisGMA yielded composites with reduced water uptake. The higher network density of the polymer matrix with methacrylated BisGMA resulted in a higher glass transition temperature Tg and a higher storage modulus of the composites. The initial temperature of weight loss of composites with VT was increased from 230°C for composites with BisGMA up to 258°C for composites with BisGMA methacrylated to a degree of 40%.

Synthesis, thermal properties, and flame retardancy of phosphorus containing polyimides

Phosphorus containing polyimides were prepared via phosphorylation of organosoluble polyimides. This was achieved by phenoxaphosphine oxide ring formation reaction or esterification with diethylchlorophosphate. The phosphorylation was confirmed by infrared, 31P nuclear magnetic resonance, and elemental analysis for phosphorus. Polyimides containing phosphorus of 8.3 and 5.4% by weight were found. Thermal characteristics and decomposition behavior of the resulting polyimides were investigated by differential scanning calorimetry and thermogravimetric analysis. Introduction of phosphorus into polyimides slightly reduced their initial weight loss temperatures and led to high char yields at temperatures higher than 800°C. Limiting oxygen index values higher than 48 were found for the phosphorylated polyimides. Such properties make these polymers useful in flame retardant applications. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 875–882, 1997

Thermal properties of sulfo-containing cation exchangers based on copolymers of vinylidene fluoride

It was found that when sulfo-containing cation exchangers based on PVDF and its copolymers are heated in air, the reaction of dehydrofluorination of the sulfonated unit in VDF takes place in the 50–100°C temperature region and the reaction of formation of sulfones with the participation of sulfo groups and macromolecules of the polymer takes place in the 220–250°C region. Treating sulfo-containing PVDF cation exchangers with an excess of ammonia with subsequent heat treatment at 110°C and reduction with hydrochloric acid increases the thermal stability of the sulfo-containing cation exchangers, and the temperature of initial weight loss is 200°C. The apparent activation energies of dehydrofluorination, formation of sulfones, and degradation of the macromolecular chain were determined and were in satisfactory agreement with the published data.

Oxidation behaviour of matrix-modified carbon-carbon composites at high temperature

The approach of matrix modification has been used to increase the high-temperature oxidation resistance of carbon-carbon composites. A distinct effect has been obtained, and the oxidation law of matrix-modified composites at high temperature has been investigated. Initially, the change in weight loss with oxidation time for matrix-modified carbon-carbon composites at constant temperature was studied. The results show that the oxidation process can be divided into three stages: a linear stage (1) with the weight loss increasing from 0 to 60%, an exponential stage (2) with weight losses between 60% and 80%, and a linear stage (3) with weight losses from 80% to 100%. Also, the variation of weight loss with oxidation temperature for matrix-modified carbon-carbon composites at constant oxidation time was measured. The results showed that this variation could be divided into three stages: a constant weight stage from ambient temperature to the temperature of initial weight loss, an exponential stage from the commencement of initial weight loss to a residual weight of about 70%, and a linear stage as the residual weight falls from 70% to 0. A mathematical theory for the three stages has been derived and tested. This treatment may prove useful for improving the high-temperature oxidation resistance of carbon-carbon composites and their properties in service.

Thermal degradation of segmented polyurethanes

AbstractThermal degradation of polyurethane samples was studied by a thermogravimetric method. The effect of soft‐segment length and soft‐segment concentration on activation energy of the degradation process was measured. Three methods of calculation gave activation energies at different stages of the very complex weight loss process. It was shown that at initial stages of the weight loss the process was dominated by hard‐segment degradation. Activation energy of the whole process calculated by the Ozawa–Flynn method did not offer clear insight into the structure–stability relationship of polyurethanes. The second method showed that activation energy of the initial stage of degradation increased with decrease in hard‐segment length. The Flynn method of calculating activation energy produced fairly constant activation energy of the first 40% degradation, at around 150 kJ/mol, for polymers in the C series. Generally, calculation of kinetic parameters of a complex degradation process as in polyurethanes gives results that are not easy to interpret. It has been shown qualitatively that polymers with higher soft‐segment concentration display lower initial weight loss and higher onset temperatures of degradation. © 1994 John Wiley & Sons, Inc.

Thermostability of Silicone Oil Evaluated by Thermogravimetric Method

The thermostability of silicone oil and antioxidation effects of lard containing silicone oil were evaluated by thermogravimetric (TG) and Rancimat methods.In programmed TG for silicone oil alone, the initial temperature of weight loss shifted to the higher temperature side with increase in viscosity. In programmed TG of lard samples to which silicone oil had been added, slight elevation in the initial temperature of weight loss was noted for several samples.For isothermal TG, thermostability evaluated based on the initial time of decomposition for lard samples to which a silicone oil had been added was found similar to oxidative stability measured by the Rancimat method. Antioxidant effects determined by the two methods failed to show any definite relationship with the type or amount of silicone oil added.

Pyrolysis Behavior and Themostability of Branched-Chain and Hydroxylated Straight-Chain Fatty Acid Moleculars

The weight loss behaviors and thermostability of four iso and anteiso branched-chain fatty acids, and four hydroxylated straight-chain saturated fatty acids in air and nitrogen flows were studied by thermogravimetry (TG) and derivative thermogravimetry (DTG). The branched acids showed a simple weight loss pattern in their TG and DTG curves in both air and nitrogen flows, whereas a more complicated pattern was observed for the hydroxy fatty acids. The TG and DTG curves of the fatty acids shifted to the higher-temperature side with an increase in the number of carbon atoms. The weight loss was found to be caused mainly by evaporation accompanied with a small degree of decomposition. Thermostability of the hydroxy fatty acids evaluated with initial temperature of weight loss was shown to be superior to that of the straight- and branced-chain fatty acids.