The synthesis and thermal properties of polyepichlorohydrin side-chain liquid crystal polymers

The synthesis and characterization of a new series of side-chain liquid crystal polyepichlorohydrin (PECH) polymers are described. The structures and thermal properties of the synthesized polymers were investigated using IR, NMR, polarized optical microscopy and differential scanning calorimetry. A substantial increase of the glass transition temperature with the degree of substitution of side-chain groups was observed. Polymers with a degree of substitution of side groups, of at least 60%, exhibited thermotropic liquid crystalline behaviour. The polymers present thermal liquid crystalline behaviour and form Schlieren and thread texture upon cooling from the isotropic phase, after annealing for 120 min at different temperatures. In addition, the thermal decomposition of PECHOPhPhCN was studied by thermogravimetry under both nitrogen and air environments. The temperature of the maximum decomposition rate was about 340 °C. Weight loss decreased considerably after 350 °C and was approximately 98% at 700 °C. Chemical modification of functional polymers offers a simple method for obtaining liquid crystalline polymers whose transition temperature can be tailored by varying the amount of substitution, however complete substitution cannot be achieved.     

Study on thermal cure and heat-resistant properties of N-(3-acetylenephenyl)maleimide monomer

N-(3-acetylenephenyl)maleimide (3-APMI), was synthesized by reacting 3-aminophenylacetylene (3-APA) with maleic anhydride by the usual two-step procedure that included ring-opening addition to give maleamic acid, followed by cyclodehydration to maleimide. Structure of the monomer was confirmed by Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (¹H NMR), elemental analysis (EA) and mass spectrum (MS). Thermal cure of the monomer was investigated by differential scanning calorimetry (DSC) and FTIR, then processing parameters and cure kinetics parameters were determined. The results showed that the monomer possesses excellent reactivity, whose cure peak temperature was 197.9 °C and cure reaction was almost complete after 4 h cure at 200 °C. Thermal properties of the cured monomer were determined by dynamic mechanical analysis (DMA) and the results show that glass transition temperature (represented by onset temperature of storage modulus) is high up to 460 °C. The results of thermogravimetry analysis (TGA) reveal that the cured monomer possessed excellent thermal stability, whose 10% weight loss temperature (T_10%) is 515.6 °C and char yield at 800 °C is 59.1%. All these characteristics make the 3-APMI monomer be an ideal candidate for matrix of thermo-resistant composites.     

Studies on self-promoted cure behaviors of hydroxy-containing phthalonitrile model compounds

A series of hydroxy-containing phthalonitrile model compounds (HPNM) with 1:1 molar ratio of hydroxy group to phthalonitrile unit were successfully synthesized. The molecular structures were identified by FTIR and ¹H NMR spectroscopic techniques. The model compounds can be thermally polymerized by duration at 225 °C for various times, even in the absence of curing additives. The thermal properties of the cured products were characterized by thermogravimetric analysis. Char yields (800 °C) of the final cured products were in the range 50-73%. The 5% and 10% weight loss ranged from 320 to 420 °C and 360-490 °C, respectively. Differential scanning calorimetry and FTIR were used to monitor the cure reaction. The results reveal that cure behaviors of the HPNM are closely correlated to their molecular structures, although each HPNM has a 1:1 molar ratio of hydroxy group to phthalonitrile unit. Therefore, the thermal properties of the final cured products depend mainly on the molecular structures of the corresponding HPNM, where differences in HPNM acidities should be considered and may contribute to their different cure behaviors.     

Preparation and properties of high performance bismaleimide resins based on 1,3,4-oxadiazole-containing monomers

In research towards high performance polymeric materials, two novel series of bismaleimide (BMI) resins based on 1,3,4-oxadiazole-containing monomers have been designed and prepared by the copolymeriziation reaction of 5-tert-butyl-1,3-bis[5-(4-maleimidophenyl)-1,3,4-oxadiazole-2-yl]benzene (Buoxd) or 4,4′-bis[5-(4-maleimidophenyl)-1,3,4-oxadiazole-2-yl]diphenyldimethylsilane (Sioxd) and 4,4′-bismaleimidodiphenylmethane (BMDM) in different feed ratios. The structures, thermal and dynamic mechanical properties of all the resulting BMI resins were carefully characterized by a combination of methods such as IR, DSC, TGA and DMA. Investigation of the copolymerization process has shown that with an increase of the weight ratio of Buoxd or Sioxd, melting transition temperature (T_m) of BMI monomer mixtures decreased and the exothermic polymerization temperature (T_p) increased. For all BMI monomer mixtures, a rapid polymerization process was observed in the early stage, as shown by the IR investigations. No glass transition was observed for the resulting BMI resins in the temperature range from 50 °C to 350 °C, indicating the formation of highly cross-linking networks. The initial thermal decomposition temperatures (T_d) of the BMI resins were in the range of 477-493 °C in nitrogen and 442-463 °C in the air. Dynamic mechanical analysis (DMA) of the composites made of the BMI resins and glass cloth showed high bending modulus not only at room temperature (E′, 1.9-5.3 GPa) but also at high temperature, e.g., 400 °C (E′, 1.7-4.4 GPa).     

Improved catalysis of Morita-Baylis-Hillman reaction. The strong synergic effect using both an imidazolic ionic liquid and a temperature

The effect of different catalytic conditions for the Morita-Baylis-Hillman reaction has been evaluated both experimentally and by chemometry. The use of either ultrasound at 0 °C, ultrasound with an imidazolic ionic liquid at 0 °C or the ionic liquid catalyst at 0 and 50 °C was systematically tested. A strong synergic effect, which significantly increases the reaction rates and yields, was observed when the reactions were performed using an imidazolic ionic liquid catalyst at both 0 and 50 °C.     

Thermal degradation kinetics of the biodegradable aliphatic polyester, poly(propylene succinate)

The preparation of the biodegradable aliphatic polyester poly(propylene succinate) (PPSu) using 1,3-propanediol and succinic acid is presented. Its synthesis was performed by two-stage melt polycondensation in a glass batch reactor. The polyester was characterized by gel permeation chromatography, ¹H NMR spectroscopy and differential scanning calorimetry (DSC). It has a number average molecular weight 6880 g/mol, peak temperature of melting at 44 °C for heating rate 20 °C/min and glass transition temperature at −36 °C. After melt quenching it can be made completely amorphous due to its low crystallization rate. According to thermogravimetric measurements, PPSu shows a very high thermal stability as its major decomposition rate is at 404 °C (heating rate 10 °C/min). This is very high compared with aliphatic polyesters and can be compared to the decomposition temperature of aromatic polyesters. TG and Differential TG (DTG) thermograms revealed that PPSu degradation takes place in two stages, the first being at low temperatures that corresponds to a very small mass loss of about 7%, the second at elevated temperatures being the main degradation stage. Both stages are attributed to different decomposition mechanisms as is verified from activation energy determined with isoconversional methods of Ozawa, Flyn, Wall and Friedman. The first mechanism that takes place at low temperatures is auto-catalysis with activation energy E = 157 kJ/mol while the second mechanism is a first-order reaction with E = 221 kJ/mol, as calculated by the fitting of experimental measurements.     

Synthesis and properties of a diastereopure ionic liquid with planar chirality

An imidazolium-based ionic liquid with cyclophane-type planar chirality was synthesized in an optically pure form for the first time. The resultant ionic liquid existed as a liquid at room temperature (T_g = −35 °C), and was found to be applicable as an NMR chiral shift reagent for racemic anions. Excellent robustness of the ionic liquid to a highly elevated temperature (270 °C) was proved from the viewpoints of isomerization and thermal decomposition.     

Phenylethynylnaphthalic endcapped imide oligomers with reduced cure temperatures

A series of 4-(2-phenylethynyl)-1,8-naphthalic anhydride (PENA) endcapped imide oligomers with different chemical backbones and calculated number average molecular weights (Calc’d M_n) were successfully synthesized and characterized. The PENA-endcapped imide oligomers were mixtures of mono- and double-endcapped imide oligomers with polymerization degree (P_n) of 1-5 and number average molecular weights (M_n) of 2515-3851 g/mol. determined by GPC. Study on effect of chemical structures on the curing behaviors of two model compounds: PENA-m based on PENA and PEPA-m derived from 4-phenylethynylphthalic anhydride (PEPA) revealed that PENA-m showed the cure temperature of 50 °C lower than PEPA-m and the activity energy of thermal curing reaction for PENA-m was also lower than that of PEPA-m. The PENA-endcapped imide oligomers could be melt at temperatures of >250 °C with the minimum melt viscosity of 1.2-230 Pa s at 275-301 °C and the widen melt processing windows, along with 10-40 °C lower cure temperature than the PEPA-endcapped analogue.The PENA-endcapped imide oligomers could be thermally cured at 350 °C/1 h to afford the thermally cured polyimides with good combined thermal and mechanical properties including T_g of 344-397 °C (DMA), T_d of 443-513 °C, tensile strength of as high as 54.7 MPa, flexural strength of as high as 126.1 MPa and modulus of as high as 2.3 GPa, respectively.     

Study of the pyrolysis of municipal solid waste for the production of valuable products

To obtain information on the potential of thermal conversion (pyrolysis) of municipal solid waste (MSW), a thermogravimetric study (TGA) is performed in a stream of nitrogen. Based on TGA results, pyrolysis experiments are carried out in a semi-batch reactor under inert nitrogen atmosphere. Slow pyrolysis is performed up to 550 °C (heating rate of 4 °C/min). Fast pyrolysis is performed at 450, 480, 510 and 550 °C and different input transfer rates (12 or 24 g material/min). The pyrolysis products are studied on composition and yield/distribution and investigated for their use as valuable product.The liquid obtained by slow pyrolysis separates spontaneously in a water rich product and an oily product. For all fast pyrolysis conditions, a viscous, brown oil which contains a poly(ethylene-co-propylene) wax is obtained. Composition analyses by GC/MS of the oil products (slow/fast pyrolysis) show that aliphatic hydrocarbons are the major compounds. The pyrolysis oils have high calorific value (between 35 and 44 MJ/kg), low wt% of water (around 6 wt%) and a low O/C value (between 0.2 and 0.3). The presence of waxy material is probably due to incomplete breakdown of poly(ethylene-co-propylene) present in MSW under study. The optimal pyrolysis conditions, regarding to oil yield, fuel properties, and wax yield is fast pyrolysis at 510 °C with 24 g material/min input transfer rate. The fast pyrolysis gases contain mainly hydrocarbons and have an averaged LHV around 20 MJ/Nm³. ICP-AES analyses of pyrolysis products reveal that almost none of the metals present in MSW are distributed within the liquid fractions.     

Acetylene-grafted resins derived from phenolics via azo coupling reaction

Novel phenolic resins with high ethynyl contents were realized via azo coupling reaction between phenol units and diazonium of 3-ethynylaniline. If Novolac and high-ortho Novolac resins were used as the starting materials directly, the ratio of ethynyl groups to phenolic rings was ca 70%; while the ratio was 100% for the resin from Friedel-Craft polycondensation of 4-(3-ethynylphenyl)salicyl alcohol. All the resins were readily soluble in acetone and ethanol, and meltable at temperatures below 100 °C. The resins underwent thermal addition-type cure with a broad exotherm of around 140-280 °C, and the starting curing temperature showed a downward drift with increase in the ethynyl content. The thermal properties of the cured resins, determined from thermogravimetric analysis (TGA), were considerably superior to those of Novolac- and Resole-type phenolic resins. The initial decomposition temperatures were at ca 400 °C, and the anaerobic carbon yields were ca 80% for all the resins.     

Thermal degradation behavior of poly(4-hydroxybutyric acid)

Thermal degradation behavior of poly(4-hydroxybutyric acid) (P(4HB)) was investigated by thermogravimetric and pyrolysis-gas chromatography mass spectrometric analyses under both isothermal and non-isothermal conditions. Based on the thermogravimetric analysis, it was found that two distinct processes occurred at temperatures below and above 350 °C during the non-isothermal degradation of P(4HB) samples depending on both the molecular weight and the heating rate. From ¹H NMR analysis of the residual P(4HB) molecules after isothermal degradations at different temperatures, it was confirmed that the ω-hydroxyl chain-end was remained unchanged in the residual P(4HB) molecules at temperatures below 300 °C, while the ω-chain-end of P(4HB) molecules was converted to 3-butenoyl units at temperatures above 300 °C. In contrast, the majority of the volatile products evolved during thermal degradation of P(4HB) was γ-butyrolactone regardless of the degradation temperature. From these results, it is concluded that during the thermal degradation of P(4HB), the selective formation of γ-butyrolactone via unzipping reaction from the ω-hydroxyl chain-end predominantly occurs at temperatures below 300 °C. At temperatures above 300 °C, both the cis-elimination reaction of 4HB unit and the formation of cyclic macromolecules of P(4HB) via intramolecular transesterification take place in addition to unzipping reaction from the ω-hydroxyl chain-end. Finally, the primary reaction of thermal degradation of P(4HB) at temperatures above 350 °C progresses by the cyclic rupture via intramolecular transesterification of P(4HB) molecules with a release of γ-butyrolactone as volatile product. Moreover, we carried out the thermal degradation tests for copolymer of 93 mol% of 4HB with 7 mol% of 3-hydroxybutyric acid (3HB) to examine the effect of 3HB units on thermal stability of P(4HB).     

Mechanistic modeling of the reaction kinetics of phenyl glycidyl ether (PGE) + aniline using heat flow and heat capacity profiles from modulated temperature DSC

Modulated temperature DSC (MTDSC) has been performed on phenyl glycidyl ether (PGE) + aniline in order to obtain the non-reversing heat flow and heat capacity profiles simultaneously in a wide range of cure temperatures and mixture compositions. The epoxy (PGE) conversion as determined from the former signal corresponds to the one obtained from separate high performance liquid chromatography (HPLC), while the latter signal contains information on the individual reaction steps. Optimized kinetic parameters using a mechanistic approach, including both reactive and non-reactive complexes can successfully simulate MTDSC measurements for isothermal reaction temperatures ranging from 50 to 120 °C and for non-isothermal experiments with mixture compositions corresponding to concentrations of aniline in a range from 1.68 to 6.53 mol kg⁻¹. Concentration profiles for three mixture compositions as obtained from HPLC are also well predicted. The activation energies for the primary amine and secondary amine-epoxy reaction catalyzed by hydroxyl groups are 50 and 52 kJ mol⁻¹, respectively, while the initiation of the reaction corresponds to the primary amine-epoxy reaction catalyzed by primary amine groups with an activation energy of 72 kJ mol⁻¹. A negative substitution effect can be calculated at 0.18 from the ratio of secondary amine to primary amine-epoxy reaction rate constants.     

Influence of polycaprolactone-triol addition on thermal stability of soy protein isolate based films

The influence of polycaprolatone-triol (PCL-T) on the thermal degradation properties of soy protein isolate (SPI)-based films was studied by thermogravimetry and infrared spectroscopy under nitrogen atmosphere. The results showed that in the absence of PCL-T the thermal degradation began between 292 °C (pure SPI films) and ca. 264 °C (SPI/SDS films with more than 20% of SDS), and these values decreased further to the range 250-255 °C for SPI/SDS/PCL-T films. At the same time, the temperature of maximum degradation rate (T_max) decreased from 331 °C (pure SPI film) to ca. 280 °C for SPI/SDS/PCL-T films with 39% PCL-T content. This behavior was also confirmed by the activation energy (E) values associated with the thermal degradation process. Apparently, the low thermal stability of PCL-T as compared to other film constituents, along with its plasticizer characteristics, is responsible for the decreased stability of SPI/SDS/PCL-T films. The FTIR spectra of gas products evolved during the thermal degradation indicated the formation of OH, CO₂, NH₃ and other saturated compounds, suggesting that the reaction mechanism involved simultaneous scission of the C(O)-O polyester bonds and C-N, C(O)-NH, C(O)-NH₂ and -NH₂ bonds of the protein.     

Long-term performance of poly(vinyl chloride) cables, Part 2: Migration of plasticizer

Cable samples with plasticized poly(vinyl chloride) insulations were aged in air at temperatures between 80 and 155 °C. The concentrations of the plasticizer (di-(2-ethylhexyl) phthalate, DEHP) in the insulations of the aged cables were determined by extraction of samples in tetrahydrofuran followed by analysis of the extract by liquid chromatography. The plasticizer concentration data for different ageing times were analysed by numerical methods, fitting Fick's second law with a concentration-dependent diffusivity. The analysis showed that the transport of the plasticizer to the surrounding air phase was controlled by diffusion at 120 and 155 °C with an activation energy of 89 kJ mol⁻¹. The evaporation of the plasticizer from the outer boundary was rate controlling at lower temperatures (≤100 °C). The rate of evaporation was initially constant and independent of the plasticizer concentration at both 80 and 100 °C. The activation energy for the initial DEHP loss rate from PVC at these temperatures was the same as that obtained for evaporation of pure DEHP on a glass plate at 60-100 °C measured by thermogravimetry, 98 ± 2 kJ mol⁻¹. Furthermore, the evaporation rate of pure DEHP on a glass plate was also of the same order of magnitude as the rate of plasticizer loss from the cable insulation. Extrapolation of the plasticizer loss rate data (from the cable at 80 °C and from pure liquid DEHP at temperatures between 60 and 100 °C) to 25 °C predicted a maximum loss of plasticizer of 1% over 25 years. This is in accordance with earlier presented data and with the data presented in this report.     

A simple method for the evaluation of heat resistant property of elastomers

The paper shows a simple method that provides us the induction period, rate of weight increase at an earlier stage of thermal oxidation of elastomer and the rate of weight loss by oxidative degradation from a certain period of aging time. Ethylene-propylene elastomer (EPR) was aged in air at various constant temperatures ranged from 90 °C to 130 °C. The weight of samples was measured periodically at room temperature. The weight increased after a certain period of induction period at the early stage of aging. The activation energy obtained from the reciprocal of the induction period and that of the rate of weight increase was the same. The values were 113 kJ/mol. The weight started to decrease from the maximum point. The activation energy for the tangent of decrease curve was 60.3 kJ/mol. This method was applied to study the effect of pre-irradiation of EPR in air on the heat resistant property of the sample. The relatively low dose of 40 kGy decreased the induction period.     

The effects of thermal treatment on the antioxidant activity of polyaniline

The thermal stability of chemically synthesized polyaniline (PANI) was examined, including granular (G) polyaniline powders formed conventionally in an HCl medium, and nanorod (NR) samples prepared using a falling-pH synthesis. The samples were examined before and after dedoping (dd) using thermogravimetric analysis (TGA), which showed small mass losses in the 200-300 °C temperature range, and greater mass losses due to oxidative degradation at higher temperatures. Furthermore, samples were treated thermally at 100, 125, 150, 175, 200, 250 and 300 °C for 30 min in air. SEM images did not show any pronounced effect on the morphologies of the samples from thermal treatment up to 300 °C. The ratios of the intensities (Q/B) of the predominantly quinonoid (Q) and benzenoid peaks (B) from FTIR spectroscopic analysis revealed that NR-PANI and NR-PANIdd underwent cross-linking upon thermal treatment up to 175 °C and were oxidized after treatment above 175 °C. G-PANI and G-PANIdd also underwent the same chemical changes with oxidation occurring above 200 °C. The free radical scavenging capacity of the samples was evaluated using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay, and was found to be independent of the spin concentrations of the samples. All samples exhibited a rapid decline in free radical scavenging capacity when exposed to temperatures above 200 °C, indicating that any polymer processing should be undertaken at temperatures less than this value to achieve high antioxidant activity.     

Thermal stability of microencapsulated epoxy resins with poly(urea-formaldehyde)

A series of microcapsules filled with epoxy resins with poly(urea-formaldehyde) (PUF) shell were synthesized by in situ polymerization, and they were heat-treated for 2 h at 100 °C, 120 °C, 140 °C, 160 °C, 180 °C and 200 °C. The effects of surface morphology, wall shell thickness and diameter on the thermal stability of microcapsules were investigated. The chemical structure and surface morphology of microcapsules were investigated using Fourier-transform infrared spectroscope (FTIR) and scanning electron microscope (SEM), respectively. The thermal properties of microcapsules were investigated by thermogravimetric analysis (TGA and DTA) and by differential scanning calorimetry (DSC). The thermal damage mechanisms of microcapsules at lower temperature (<251 °C) are the diffusion of the core material out of the wall shell or the breakage of the wall shell owing to the mismatch of the thermal expansion of core and shell materials of microcapsules. The thermal damage mechanisms of microcapsules at higher temperature (>251 °C) are the decomposition of shell material and core materials. Increasing the wall shell thickness and surface compactness can enhance significantly the weight loss temperatures (T_d) of microcapsules. The microcapsules with mean wall shell thickness of 30 ± 5 μm and smoother surface exhibit higher thermal stability and can maintain quite intact up to approximately 180 °C.     

Investigation on Ochratoxin A stability using different extraction techniques

The stability of Ochratoxin A during its extraction using different extraction techniques has been evaluated. Microwave-assisted extraction and pressurised liquid extraction, in addition to two other reference methods of extraction, i.e. ultrasound-assisted and magnetic stirring-assisted extraction, were evaluated. The effect of extraction temperature using the cited techniques was checked.The results show that Ochratoxin A can be extracted using microwave-assisted extraction at temperatures up to 150 °C without degradation. Pressurised liquid extraction can be used at temperatures up to 100 °C, for extraction times of less than 30 min. Further, both ultrasound-assisted extraction and magnetic stirring extraction can be applied at temperatures up to 65 °C.High-performance liquid chromatography combined with fluorescence detection using a Chromolith RP-18e column at a flow rate of 5 mL min⁻¹ was used to quantify the Ochratoxin A. The retention time for the Ochratoxin A was 1.3 min. The limits of detection (LOD) and of quantification (LOQ) were 0.03 and 0.10 μg L⁻¹, respectively.     

High-throughput salting-out assisted liquid/liquid extraction with acetonitrile for the simultaneous determination of simvastatin and simvastatin acid in human plasma with liquid chromatography

Simvastatin (SS) is an effective cholesterol-lowering medicine, and is hydrolyzed to simvastatin acid (SSA) after oral administration. Due to SS and SSA inter-conversion and its pH and temperature dependence, SS and SSA quantitation is analytically challenging. Here we report a high-throughput salting-out assisted liquid/liquid extraction (SALLE) method with acetonitrile and mass spectrometry compatible salts for simultaneous LC-MS/MS analysis of SS and SSA. The sample preparation of a 96-well plate using SALLE was completed within 20 min, and the SALLE extract was diluted and injected into an LC-MS/MS system with a cycle time of 2.0 min/sample. The seamless interface of SALLE and LC-MS eliminated drying down step and thus potential sample exposure to room or higher temperature. The stability of SS and SSA in various concentration ratios in plasma was evaluated at room and low (4 °C) temperature and the low temperature (4 °C) was found necessary to maintain sample integrity. The short sample preparation time along with controlled temperature (2-4 °C) and acidity (pH 4.5) throughout sample preparation minimized the conversion of SS → SSA to ≤0.10% and the conversion of SSA → SS to 0.00% The method was validated with a lower limit of quantitation (LLOQ) of 0.094 ng mL⁻¹ for both SS and SSA and a sample volume of 100 μL. The method was used for a bioequivalence study with 4048 samples. Incurred sample reproducibility (ISR) analysis of 362 samples from the study exceeded ISR requirement with 99% re-analysis results within 100 ± 20% of the original analysis results.     

Thermal decomposition and stability of fatty acid methyl esters in supercritical methanol

In recent years, non-catalytic supercritical processes for biodiesel production have been proposed as alternative environmentally friendly technologies. However, conditions of high temperature and pressure that occur while biodiesel is in supercritical fluid can cause fuel degradation, resulting in low yield. In this study, we performed the thermal decomposition of fatty acid methyl esters (FAMEs) in supercritical methanol at temperatures ranging from 325 °C to 420 °C and pressure of 23 MPa to investigate the degradation characteristics and thermal stability of biodiesel. The primary reactions we observed were isomerization, hydrogenation, and pyrolysis of FAMEs. The main pathway of degradation was deduced by analyzing the contents of degradation products. We found that if FAME has shorter chain length or is more saturated, it has higher thermal stability in supercritical methanol. All FAMEs remained stable at 325 °C or below. Based on these results, we recommend that transesterification reactions in supercritical methanol should be carried out below 325 °C (at 23 MPa) and 20 min, the temperature at which thermal decomposition of FAMEs begins to occur, to optimize high-yield biodiesel production.