A new approach to prepare high molecular weight poly(p-dioxanone) by chain-extending from dihydroxyl terminated propolymers

As poly(p-dioxanone) (PPDO) with a high molecular weight (viscosity-average molecular weight (M_ν) > 100,000 g/mol) is not easy to be obtained in a short time, a new approach has been developed to produce high molecular weight poly(p-dioxanone) (HPPDO-T) by chain-extending reaction of hydroxyl-terminated PPDO (HPPDO) prepolymers using toluene-2,4-diisocyanate (TDI) as chain extender. Here HPPDO prepolymers were synthesized via ring-opening polymerization of p-dioxanone (PDO) monomer initiated by 1,4-butanediol (BD) with Stannous octoate (SnOct₂) as catalyst. The resulting polymers, having a highest M_ν of 250,000 g/mol, were characterized by ¹H NMR, TG, DSC and WXRD. HPPDO prepolymers can react with TDI more effectively than the PPDO prepolymers initiated by mono-functional initiators, and the molecular weights of resulting chain-extended products increase several decade times in an hour comparing to the prepolymers. The chain extended products HPPDO-T have better thermal stability, and higher glass transition temperatures and lower crystallization rates than PPDO homopolymer.     

A facile approach to preparation of long-chain-branched poly(p-dioxanone)

Long-chain-branched poly(p-dioxanone)s (LCB-PPDOs) with different branch densities were prepared via the chain-extending reaction of hydroxyl group terminated linear bi-functional PPDO (2a-PPDO) and star-like tri-functional PPDO (3a-PPDO) prepolymers, which were synthesized by the ring-opening polymerization of p-dioxanone (PDO) using 1,4-butanediol (BD) and trimethylolpropane (TMP) as multi-functional initiators, respectively. The undesirable gelation was successfully depressed by adjusting the chain length and feed ratio of prepolymers. The average molecular weight between branch points (M_b) and the average number of branch per 100,000 g/mol (B_n) of LCB-PPDOs were calculated from the ¹H NMR spectra. The average number of branch ranged from 0 to 6.72 branch points per 100,000 g/mol, and the number-average molecular weights between branch points ranged from 6900 to 20,500 g/mol. The results of differential scanning calorimetry (DSC) showed that the crystallization behavior of LCB-PPDOs was changed evidently with the branch density. Small-amplitude dynamic oscillatory rheometer was used to investigate the rheological properties of the melts of LCB-PPDO including zero-shear viscosity, storage modulus, relaxation times and loss angle, which largely depended on the branch density and length of LCB-PPDOs. Therefore, the rheological behaviors of PPDO can be well-controlled via synthesizing LCB-PPDOs with the desired architectures.     

Evaluation of kinetics parameters for poly(l-lactic acid) hydrolysis under high-pressure steam

In order to evaluate more precise kinetics parameters: rate constant k and E_a values for poly(l-lactic acid) hydrolysis, the reaction was carried out under high-pressure steam in a temperature range of 100-130 °C. Molecular weights of hydrolyzates were calculated by the universal calibration method without being influenced by any weight loss. The changes in molecular weight could be successfully explained according to the auto-catalytic hydrolysis mechanism, clearly indicating the critical point. Resulting k and E_a values were estimated as 8.4 × 10⁻⁵-7.2 × 10⁻⁴ s⁻¹ and 87.2 kJ mol⁻¹ with high R² values, respectively. Moreover, to determine the deviation of the parameter values, influences of four factors on the measurements and calculation: (1) use of number-average molecular weight value alone, (2) use of relative molecular weight based on polystyrene standards, (3) weight loss during the hydrolysis, and (4) selection of reaction mechanism were evaluated quantitatively.     

The decomposition kinetics of [Et4N]2[M(dmit)2] (M = Ni, Pd) in a nitrogen atmosphere using thermogravimetry

Thermal properties and thermal decompositions of [NEt₄]₂[M(dmit)₂] (M = Ni(II), Pd(II), dmit = 1,3-dithiole-2-thione-4,5-dithiolate) have been studied by thermogravimetry (TG). The TG analysis has shown that the complexes are thermally stable up to 460 K and the decomposition of the complexes occurs in three consecutive stages up to 873 K. A thermal stability scale for [M(dmit)₂]ⁿ⁻ anions was based on the thermal properties. Kinetics parameters, such as activation energy, E_a, and kinetic apparent pre-exponential factor, ln A_app, have been calculated from the thermogravimetric data at heating rates of 10, 15, 20 and 25 K/min involving differential (Friedman's equation) and integral (Flynn-Wall-Ozawa's equation) methods.     

Viscoelasticity and thermal stability of polylactide composites with various functionalized carbon nanotubes

Polylactide (PLA) nanocomposites containing various functionalized multi-walled carbon nanotubes (MWCNTs) were prepared directly by melt compounding. The linear rheology and thermal stability of the PLA nanocomposites were, respectively, investigated by the parallel plate rheometer and TGA, aiming at examining the effect of surface functionalization on the dispersion of MWCNTs by using viscoelastic and thermal properties. Among three MWCNTs used in this work, the carboxylic MWCNTs present better dispersion in PLA matrix than the hydroxy and purified MWCNTs because the corresponding composite shows the lowest rheological percolation threshold, which is further confirmed by the TEM and solution experiments. The presence of all these three MWCNTs, however, nearly cannot improve the thermal stability effectively at the initial stage of degradation and the temperature corresponding to a weight loss of 5 wt% (T_5 wt%) only shows slight increase in contrast to that of the neat PLA while with increase of decomposition level, the presence of carboxylic and purified MWCNTs retards the depolymerization of PLA evidently, showing remarkable increase in the temperature corresponding to maximum rate of decomposition (T_max). Both the dispersion state and the surface functionalization of MWCNTs are very important to the thermal stability of PLA matrix.     

Kinetics of thermal degradation and thermal oxidative degradation of poly(p-dioxanone)

The kinetics of the thermal degradation and thermal oxidative degradation of poly(p-dioxanone) (PPDO) were investigated by thermogravimetric analysis. Kissinger method, Friedman method, Flynn-Wall-Ozawa method and Coats-Redfern method have been used to determine the activation energies of PPDO degradation. The results showed that the thermal stability of PPDO in pure nitrogen is higher than that in air atmosphere. The analyses of the solid-state processes mechanism of PPDO by Coats-Redfern method and Criado et al. method showed: the thermal degradation process of PPDO goes to a mechanism involving random nucleation with one nucleus on the individual particle (F₁ mechanism); otherwise, the thermal oxidative degradation process of PPDO is corresponding to a nucleation and growth mechanism (A₂ mechanism).     

Effect of PEG on the crystallization of PPDO/PEG blends

A new biodegradable polymer system, poly(p-dioxanone) (PPDO)/poly(ethylene glycol) (PEG) blend was prepared by a solvent casting method using chloroform as a co-solvent. The PPDO/PEG blends have different weight ratios of 95/5, 90/10, 80/20 and 70/30. Crystallization of homopolymers and blends were investigated by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). When 5% of PEG was blended, the crystallization exothermal peaks (T_c) of PPDO increased sharply and the crystallization exothermal peaks (T_c) of PEG decreased slightly compared with the homopolymers. The crystallization rates of both components increased, and caused greater relative crystallization degree (X_t%). But when the content of PEG was more than 5%, the crystalline behaviors of blends had no more significant changes accordingly. The melting points of each sample varied little over the entire composition range in this study. The nonisothermal crystallization of PPDO homopolymer and blend (PPDO/PEG = 70/30) were also studied by DSC. The crystallization began at a higher temperature when the cooling rates were slower. The nonisothermal crystallization kinetics of blends was analyzed by Ozawa equation. The results showed that the Ozawa equation failed to describe the whole crystallization of the blend, but Mo equation could depict the nonisothermal crystallization perfectly.     

Tin(II)-EDTA complex: kinetic of thermal decomposition by non-isothermal procedures

Tin on the oxide form, alone or doped with others metals, has been extensively used as gas sensor, thus, this work reports on the preparation and kinetic parameters regarding the thermal decomposition of Sn(II)-ethylenediaminetetraacetate as precursor to SnO₂. Thus, the acquaintance with the kinetic model regarding the thermal decomposition of the tin complex may leave the door open to foresee, whether it is possible to get thin film of SnO₂ using Sn(II)-EDTA as precursor besides the influence of dopants added.The Sn(II)-EDTA soluble complex was prepared in aqueous medium by adding of tin(II) chloride acid solution to equimolar amount of ammonium salt from EDTA under N₂ atmosphere and temperature of 50 °C arising the pH∼4. The compound was crystallized in ethanol at low-temperature and filtered to eliminate the chloride ions, obtaining the heptacoordinated chelate with the composition H₂SnH₂O(CH₂N(CH₂COO)₂)₂·0.5H₂O.Results from TG, DTG and DSC curves under inert and oxidizing atmospheres indicate the presence of water coordinated to the metal and that the ethylenediamine fraction is thermally more stable than carboxylate groups. The final residue from thermal decomposition was the SnO₂ characterized by X-ray as a tetragonal rutile phase.Applying the isoconversional Wall-Flynn-Ozawa method on the DSC curves, average activation energy: E_a=183.7±2.7 and 218.9±2.1 kJ mol⁻¹, and pre-exponential factor: and 19.10±0.27 min⁻¹, at 95% confidence level, could be obtained, regarding the loss of coordinated water and thermal decomposition of the carboxylate groups, respectively. The E_a and log A also could be obtained applying isoconventional Wall-Flynn method on the TG curves.From E_a and log A values, Dollimore and Malék procedures could be applied suggesting R3 (contracting volume) and SB (two-parameter model) as the kinetic model to the loss of coordinated water (177-244 °C) and thermal decomposition of the carboxylate groups (283-315 °C), respectively. Simulated and experimental normalized DTG and DSC curves besides analysis of residuals check these kinetic models.     

Kinetic studies of the decomposition of flame retardant containing high-impact polystyrene

The thermal decomposition of flame retardant free high-impact polystyrene (HIPS) and four HIPS samples containing brominated flame retardants has been studied using TGA at different heating rates between 2.5 and 10 K min⁻¹. Decabromodiphenyl ether (DPE) and decabromodibenzyl (DDB) were used as flame retardants, and two of the samples contained antimony trioxide (Sb₂O₃) synergist besides the brominated additives. The activation energies (E_A) and frequency factors (k₀) were calculated by the methods of Kissinger and Ozawa. A compensation effect was observed and used for the identification of changes in the degradation kinetics. In a third step, the kinetic model of the reaction was determined. Both Kissinger and Ozawa showed that the HIPS degraded with an E_A of 200 kJ mol⁻¹. The choice of the flame retardant had, however, little impact on the TGA plot. The addition of a flame retardant as well as the addition of Sb₂O₃ reduced the E_A. Fire retardant free HIPS degraded mainly by power-law kinetics, while the addition of a flame retardant caused the mechanism to change to a phase-boundary controlled mechanism after a weight loss of 80 wt%.     

Thermal degradation mechanism of poly(ethylene succinate) and poly(butylene succinate): Comparative study

Two aliphatic polyesters that consisted from succinic acid, ethylene glycol and butylene glycol, —poly(ethylene succinate) (PESu) and poly(butylene succinate) (PBSu)—, were prepared by melt polycondensation process in a glass batch reactor. These polyesters were characterized by DSC, ¹H NMR and molecular weight distribution. Their number average molecular weight is almost identical in both polyesters, close to 7000 g/mol, as well as their carboxyl end groups (80 eq/10⁶ g). From TG and Differential TG (DTG) thermograms it was found that the decomposition step appears at a temperature 399 °C for PBSu and 413 °C for PESu. This is an indication that PESu is more stable than PBSu and that chemical structure plays an important role in the thermal decomposition process. In both polyesters degradation takes place in two stages, the first that corresponds to a very small mass loss, and the second at elevated temperatures being the main degradation stage. The two stages are attributed to different decomposition mechanisms as is verified from the values of activation energy determined with iso-conversional methods of Ozawa, Flyn, Wall and Friedman. The first mechanism that takes place at low temperatures, is auto-catalysis with activation energy E = 128 and E = 182 kJ/mol and reaction order n = 0.75 and 1.84 for PBSu and PESu, respectively. The second mechanism is nth-order reaction with E = 189 and 256 kJ/mol and reaction order n = 0.68 and 0.96 for PBSu and PESu, respectively, as they were calculated from the fitting of experimental results.     

Modeling of the three-phase equilibrium in systems of the type water + nonionic surfactant + alkane

Liquid–liquid equilibria of systems water (A) + C_iE_j surfactant (B) + n-alkane (C) have been modeled by a mass-action law model previously developed and so far successfully applied to a series of binary water + C_iE_j systems and to the ternary system water + C₄E₁ + n-dodecane. These calculations provide the basis for the presented modeling. The aqueous systems give information about the association constants and the χ_AB-parameter of the Flory–Huggins theory and the ternary C₄E₁-system provides universal temperature functions for the χ_AC- and the χ_BC-parameter. The three-phase equilibrium for seven ternary C_iE_j systems (i = 6–12, j = 3–6) has been calculated by fitting one additional parameter for each of both temperature functions to the characteristic “fish-tail” point. The agreement with the experimental data is reasonably well. For systems with very small three-phase areas the results can considerably be improved by individual temperature functions that incorporate the experimental temperature maximum of the “fish” into the parameter fit. Based on the parameters of the system water + C₈E₄ + n-C₈H₁₈ the “fish-shaped” phase diagram of the system water + C₈E₄ + n-C₁₄H₃₀ was predicted reasonably well.     

Thermal and rheological behaviours of some random aromatic amino-ended polyethersulfone/polyetherethersulfone copolymers

The thermal and rheological characterizations of seven random, low molecular weight (M_n ≅ 9500 g mol⁻¹), H₂N-ended polyethersulfone/polyetherethersulfone (PES/PEES) copolymers, at various PES/PEES ratios, were performed. The glass transition temperatures (T_g) were determined by DSC. Degradations were carried out in a thermobalance, under flowing nitrogen, in dynamic heating conditions from 35 °C to 650 °C. The initial decomposition temperatures (T_i) and the half decomposition temperatures (T_1/2) were directly determined by TG curves, while the apparent activation energies of degradation (E_a) were obtained by the Kissinger method. In addition, the complex viscosities (η^∗) of the molten polymers were determined in experimental conditions of linear viscoelasticity. T_g, E_a and η^∗ values increased linearly with PES% content, while T_i and T_1/2 values showed opposite behaviour. In every case both PES and PEES homopolymers felt outside linearity. The results obtained are discussed and interpreted, and compared with those of corresponding Cl-ended copolymers previously studied.     

Heat capacity and thermodynamic properties of crystalline ornidazole (C7H10ClN3O3)

The molar heat capacities of 1-(2-hydroxy-3-chloropropyl)-2-methyl-5-nitroimidazole (Ornidazole) (C₇H₁₀ClN₃O₃) with purity of 99.72 mol% were measured with an adiabatic calorimeter in the temperature range between 79 and 380 K. The melting-point temperature, molar enthalpy, Δ_fusH_m, and entropy, Δ_fusS_m, of fusion of this compound were determined to be 358.59±0.04 K, 21.38±0.02 kJ mol⁻¹ and 59.61±0.05 J K⁻¹ mol⁻¹, respectively, from fractional melting experiments. The thermodynamic function data relative to the reference temperature (298.15 K) were calculated based on the heat capacities measurements in the temperature range from 80 to 380 K. The thermal stability of the compound was further investigated by DSC and TG. From the DSC curve an intensive exothermic peak assigned to the thermal decomposition of the compound was observed in the range of 445-590 K with the peak temperature of 505 K. Subsequently, a slow exothermic effect appears when the temperature is higher than 590 K, which is probably due to the further decomposition of the compound. The TG curve indicates the mass loss of the sample starts at about 440 K, which corresponds to the decomposition of the sample.     

Effect of clay on the corrosion protection efficiency of PMMA/Na-MMT clay nanocomposite coatings evaluated by electrochemical measurements

The preparation of PMMA-clay nanocomposites was investigated by using sodium dodecylbenzenesulfonate (SDS) and potassium peroxodisulfate (KPS) as a surfactant and chain initiator for an in situ emulsion polymerization reaction, respectively. The as-prepared nanocomposites were then characterized by Fourier transformation infrared (FTIR) spectroscopy, wide-angle X-ray diffraction (WAXRD) patterns and transmission electron microscopy (TEM).It should be noted that the nanocomposite coating containing 1 wt% of clay loading was found to exhibit an observable enhanced corrosion protection on cold-rolled steel (CRS) electrode at higher operational temperature of 50 °C, which was even better than that of uncoated and electrode-coated with PMMA alone at room temperature of 30 °C based on the electrochemical parameter evaluations (e.g., E_corr, R_p, I_corr, R_corr and impedance). In this work, all electrochemical measurements were performed at a double-wall jacketed cell, covered with a glass plate, through which water was circulated from a thermostat to maintain a constant operational temperature of 30, 40 and 50 ± 0.5 °C. Moreover, a series of electrochemical parameters shown in Tafel, Nyquist and Bode plots were all used to evaluate PCN coatings at three different operational temperatures in 5 wt% aqueous NaCl electrolyte. The molecular barrier properties at three different operational temperatures of PMMA and PCN membranes were investigated by gas permeability analyzer (GPA) and vapor permeability analyzer (VPA). Effect of material composition on the molecular weight and optical properties of neat PMMA and PCN materials, in the form of solution and membrane, were also studied by gel permeation chromatography (GPC) and UV-vis transmission spectra.     

Thermal and photochemical stability of poly(vinyl alcohol)/modified lignin blends

A kraft lignin derivative (KLD) obtained by reaction with p-aminobenzoic acid/phthalic anhydride was blended with poly(vinyl alcohol) (PVA) by solution casting from DMSO. PVA and PVA/KLD films were exposed to ultraviolet radiation (24, 48, and 96 h) and analyzed by thermogravimetry (TG), differential scanning calorimetry (DSC), infrared spectroscopy (FTIR), hydrogen nuclear magnetic resonance (¹H NMR) spectroscopy, and scanning electron microscopy (SEM). PVA films show a loss of thermal stability due to irradiation. PVA/KLD reveals greater thermal stability than PVA and an increase in thermal stability after irradiation. These results suggest that the incorporation of KLD into PVA provides a gain in thermal and photochemical stability. FTIR, ¹H NMR, DSC, and TG results obtained for the blends suggest that intermolecular interactions between PVA and KLD chains are present. SEM micrographs revealed blend miscibility for a KLD blend content of up to 15 wt%, as observed at magnification of 1000 times.     

Reducing the formation of six-membered ring ester during thermal degradation of biodegradable PHBV to enhance its thermal stability

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) has attracted the attention of academia and industry because of its biodegradability, biocompatibility, thermoplasticity and plastic-like properties. However, PHBV is unstable above 160 °C during melt processing at a temperature above the melting temperature, which restricts practical applications as a commodity material. It is widely believed that thermal degradation of PHBV occurs almost exclusively via a random chain scission mechanism involving a six-membered ring transition state. Here, 2,2′-bis(2-oxazoline) (BOX) was selected to modify PHBV to control the formation of six-membered ring ester during thermal degradation. The resulting hydroxyl-terminated PHBVs (HT-PHBVs) had improved thermal stability due to a decrease in the negative inductive effect of the neighboring group of methylene groups at the β-position to the ester oxygen, and a decrease in the electron-denoting effect of substituent group of carbon atoms at α-position to the ester oxygen. The optimal reaction temperature and time were determined to be 95 °C and 6 h, respectively. Compared with those of original PHBV, the temperature determined at 5% weight loss (T_5%), the initial decomposition temperature (T₀), the maximum decomposition temperature (T_max), the complete decomposition temperature (T_f) of HT-PHBV prepared under the optimal conditions increased by 31, 24, 19 and 19.1 °C, respectively.     

Thermal degradation behavior of radiation synthesized polydiallyldimethylammonium chloride

Thermogravimetric analysis (TGA) and differential scanning calorimetric (DSC) studies were carried out on gamma radiation synthesized polydiallyldimethylammonium chloride (PDADMAC). The polymer was found to undergo thermal degradation in two stages. The first stage showed a weight loss of 33% and the second stage showed a weight loss of 67%. The DSC thermogram shows two endothermic peaks corresponding to the two stages in the TG thermogram and the experimental enthalpy change associated with the first and second stages were 650 J g⁻¹ and 129.5 J g⁻¹, respectively. The nth-order kinetic parameters (order of the reaction, activation energy and the pre-exponential factor) were determined from a single dynamic DSC or thermogravimetric (TG) thermogram by the method of least square. Theoretical TG/differential thermogravimetric (DTG) and DSC thermograms derived from the calculated kinetic parameters were in good agreement with the experimental ones at the heating rate employed. However, the kinetic parameters determined using TG and DSC were different. This leads to the conclusion that the degradation mechanism could be complicated and may consists of a number of parallel or consecutive reactions. The glass transition temperature (T_g) of the polymer was found to be around 150 °C depending on the test method employed.     

The influence of chain rigidity on the thermal properties of some novel random copolyethersulfones

Some random low molar mass (M_n ≈ 9000 g mol⁻¹) poly(ethersulfoneethersulfone)/poly(ethersulfoneethersulfonebiphenylsulfone) P(ESES)/P(ESESBS) copolymers, with various (25%, 50% and 75%) ESESBS units contents, were synthesized to obtain compounds with higher chain rigidity than PES. The thermal characterization of the prepared copolymers, as well as that of corresponding P(ESES) and P(ESESBS) homopolymers, was performed, and all investigated parameters showed strong dependence on polymer composition.The glass transition temperature (T_g) was calorimetrically determined by DSC technique, and the obtained values increased linearly as function of ESESBS units percentage, thus indicating an increasing chain rigidity.Degradations were carried out in dynamic heating conditions, from 35 °C to 700 °C, in both flowing nitrogen and static air atmosphere, and the characteristic parameters of degradation were determined in order to draw useful information about the overall thermal stability of the studied compounds. The apparent activation energy of degradation (E_a) was obtained by the Kissinger method, and the values found increased linearly as a function of ESESBS content, while the temperature values at 5% mass loss (T_5%) showed an opposite linear trend. The results are discussed and interpreted.     

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.     

Study of oxidation properties and decomposition kinetics of three-dimensional (3-D) braided carbon fiber

The XRD, SEM, isothermal oxidation-weight loss and non-isothermal thermogravimetry (TG)-differential thermogravimetry (DTG) were used to study the oxidation properties and oxidation decomposition kinetics of three-dimensional (3-D) braided carbon fiber (abbreviated as fiber). The results showed that the non-isothermal oxidation process of fiber exhibited self-catalytic characteristic. The kinetic parameters and oxidation mechanism of fiber were studied through analyzing the TG and DTG data by differential and integral methods. The oxidation mechanism was random nucleation, the kinetic parameters were: lg A=10.299 min⁻¹; E_a=156.29 kJ mol⁻¹.