Polymers from Renewable Resources. Xiv. Interpenetrating Polymer Networks Derived from Castor Oil—Isophorone Diisocyanate-Polyacrylamide: Thermal,Scanning Electron Microscopy,and Xrd Studies

Abstract

A large number of castor oil based polyurethanes were prepared using various diisocyanates such as isophorone diisocyanate varying the NCO/OH ratio. All the polyurethanes were reacted with acrylamide and methacrylamide using ethylene glycol dimethacrylate as crosslinker and benzoyl peroxide as initiator. Thermogravimetric analysis of the polymers were followed using computer analysis method for assigning the kinetic mechanism. The degradation steps have been discussed in the light of kinetic parameters. The SEM of some of the IPNs has been studied and the morphology has been examined. The samples were subjected to wide angle X-ray diffraction analysis. Ruland and Vonk method was used to calculate the degree of crystallinity (X_cr).     

A thermogravimetric analyzer for condensable gas adsorption under subatmospheric conditions

Potential alternative to petrochemical polymers, soy protein isolate (SPI), a plentily available, natural biopolymer is chemically modified with thiourea at 2.5, 5, 7.5, 10, 15 and 20 mass/mass% for better processing of plastic as a raw material. From the FTIR studies, it has been ascertained that there is no bonding reaction between SPI and thiourea and it acts as a modifier only. Thermogravimetric analysis of the modified material has been followed using a computer analysis method, LOTUS package, developed by us for assigning the degradation mechanism. A number of equations have been used to evaluate the kinetic parameters. The mechanism of degradation of the biopolymer is explained on the basis of the kinetic analysis.     

Kinetics and mechanism of zinc(II), cadmium(II), and mercury(II) incorporation into meso tetrameta-tolueneporphyrin

The kinetics of Zn(II), Cd(II), and Hg(II) incorporation into meso tetrameta-tolueneporphyri n (H₂T(m-CH₃)PP) in acetone have been studied by means of stopped-flow method. A unified reaction mechanism was proposed and the kinetic parameters were obtained by nonlinear least-square methods. The effect of ionic strength (I) on Cd(II)/H₂T(m-CH₃)PP was investigated. It has been found that there is a negative kinetic salt effect and the relationship of rate constants with ionic strength was obtained. Some solvent effects have also been investigated in this article. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 277–283, 1998.     

Coordination chain polymeric assemblies of trivalent lanthanides with multidentate Schiff base synthetic, spectral investigation and thermal aspects

The coordination chain polymers of La(III), Ce(III), Pr(III), Nd(III) and Sm(III) with N,N’-di(o-thiophenyl)terephthalaldehydediimine have been prepared and characterized by elemental analysis, ¹H NMR, ¹³C NMR, magnetic measurements, infrared spectra, reflectance spectra and thermogravimetric analysis. A coordination number of seven around the metal ion is suggested. The thermal decompositions of the coordination polymers have been studied. The kinetic parameters have been calculated using Freeman-Carroll method. The thermodynamic activation parameters such as entropy (S*), preexponential factor (A), enthalpy (H*) and free energy of the decomposition (G*) have been evaluated.     

Kinetics of the oxidative degradation of d-xylose in the presence and absence of cationic and anionic surfactants

The oxidative degradation of d-xylose by cerium(IV) has been found to be slow in acidic aqueous solution with the evidence of autocatalysis. The reaction is accelerated in the cetyltrimethylammonium bromide (CTAB) micellar medium but sodium dodecyl sulfate (an anionic surfactant) has no effect. The pseudo first-order rate constants have been determined at different [reductant], [oxidant], [H₂SO₄], temperature, and [CTAB]. The reaction rate increased with increasing [d-xylose] and decreased with increase in [H₂SO₄]. The CTAB-micelle-catalyzed kinetic results can be interpreted by the pseudophase model. The kinetic parameters such as association constant (K _s), micellar medium rate constant (k _m), and activation parameters (E _a, ΔH ^# and ΔS ^#) are evaluated and the reaction mechanism is proposed. The reaction rate is inhibited by electrolytes and the results provide an evidence for the exclusion of the reactive species from the reaction site.     

Thermal degradation of polyurethanes based on xylylene diisocyanates

Polyurethanes derived from xylylene diisocyanates and trans-1,4-cyclohexanedimethanol were thermally degraded by using the techniques of thermogravimetry and pyrolysis at atmospheric pressure. Quantitative determination of the pyrolysis products such as CO₂, diamine, olefin, and starting diol showed that these polyurethanes follow the typical mechanism of degradation via dissociation into starting diol and diisocyanate. Kinetic parameters for the overall degradation reaction were determined using four different methods. The results showed the influence of the experimental technique used when making a comparison of the thermal stability of polymers, as determined by the kinetic parameters of the degradation reactions.     

Mechanism and kinetics of the isothermal thermodegradation of ethylene-propylene-diene (EPDM) elastomers

The thermal degradation behavior of a range of ethylene-propylene-diene (EPDM) elastomers, covering the whole range of composition, has been examined under isothermal conditions between 410 and 440 °C using thermogravimetric analysis. The kinetic parameters of degradation for the polymers have been evaluated using different mathematical models based on different proposed mechanisms of degradation. The experimental data were fitted to the models using non-linear regression analysis technique based on Marquardt-Levenberg algorithm. It appears that the degradation of EPDMs follows the Avrami-Erofeev two-dimensional nucleation model or a random chain-scission mechanism. No observable trend was found between the ethylene content of EPDM and the activation energy of degradation.     

Thermal and structural analysis and crystallization behavior of new poly(ether-alkyl) oxadiazoles

A new series of poly(ether-alkyl)oxadiazoles of general formula: with m = 3, 4, and 5 has been obtained from the corresponding polyhydrazides through thermal cyclization reaction. The polymers were characterized by infrared spectroscopy, differential scanning calorimetry, wide-angle x-ray analysis, and optical microscopy. The polymers were crystalline, with a crystalline texture and structural parameters strongly dependent on the value of m. The T_m's and T_g's value decreased with increasing number of CH₂. © 1994 John Wiley & Sons, Inc.     

Preparation and degradation of salts of poly(methacrylic acid). I. Lithium,sodium, potassium,and caesium salts

The polymers of lithium, sodium, potassium, and caesium salts of methacrylic acid have been prepared by free radical polymerization of the respective monomers in methanol solution. The degradation behavior of the polymers has been investigated by thermal volatilization analysis, thermogravimetry, and product analysis. These materials are stable to about 350°C under programmed heating at 10°C/min in vacuo. The principal degradation products are monomer, the corresponding isobutyrate, carbonate, oxide, carbon dioxide, and a fraction of liquid volatiles that is complex and contains a variety of aldehydes and ketones. The mechanism of degradation is discussed in detail.     

Dependence of the frequency factor on the temperature: a new integral method of nonisothermal kinetic analysis

A new integral method of nonisothermal kinetic analysis has been developed with the dependence of the frequency factor on the temperature (A = A ₀ T ^m ). The new integral method is obtained from the newly proposed approximation for the general temperature integral, which is more accurate than the other existed approximations. For applications, nonisothermal thermoanalytical data obtained by theoretical simulation have been processed. The results have shown that the newly proposed integral method is an ideal solution for the evaluation of kinetic parameters from nonisothermal thermoanalytical data with the frequency factor dependent the temperature.     

A new model for the kinetic analysis of thermal degradation of polymers driven by random scission

In this paper, a series of f(α) kinetic equations able to describe the random scission degradation of polymers is formulated in such a way that the reaction rate of the thermal degradation of polymers that go through a random scission mechanism can be directly related to the reacted fraction. The proposed equations are validated by a study of the thermal degradation of poly(butylene terephthalate) (PBT). The combined kinetic analysis of thermal degradation curves of this polymer obtained under different thermal pathways have shown that the proposed equation fits all these curves while other conventional models used in literature do not.     

Biodegradation of polymeric drug carriers: Kinetic modeling

Analytical models - based on kinetic and mechanistic considerations- have been developed, for describing the enzymic degradation of polymers. The models were applied to delineate the degradation patterns expected when endo- or exo- acting enzymes are used, and when the kinetic constant K_M varies with the size (i) of the macromolecular substrate. Utilization of these models, in conjunction with experimentally available data, provides the possibility to define the mechanism of enzymic action, and to determine the kinetic constants of the process. Thus, for example, for the degradation of poly-N-(2-hydroxyethyl)-L-glutamine (PHEG) by papain, the correlation between K_M and i was established. The above models can also be used to provide data that cannot be obtained experimentally (e.g. exact chain length distribution of degradation products), and to determine, with minimum effort, the experimental set up required for obtaining a desired array of products. They are, therefore, most useful tools for the design of enzyme–actuated drug delivery devices.     

Thermal degradation kinetics of semi-aromatic polyamide containing benzoxazole unit

The kinetics of the thermal degradation of a new semi-aromatic polyamide containing benzoxazole unit (BO6) have been investigated by thermogravimetric analysis (TG). Thermal degradation of BO6 could be accomplished by one step. The corresponding kinetic parameters of the degradation process are determined by using Kissinger and Flynn–Wall–Ozawa methods, respectively. Coats–Redfern method is also used to discuss the probable degradation mechanism of the BO6. The results show that the activation energy obtained from Kissinger method is in good agreement with the value obtained by using Flynn–Wall–Ozawa method. The solid-state degradation mechanism of the BO6 is a decelerated R ₁ type (phase boundary controlled reaction one-dimensional movement).     

Thermokinetic studies of poly(<Emphasis Type="Italic">o</Emphasis>-toluidine) doped with perchloric acid

Thermokinetic parameters of the solid-state of poly(o-toluidine) (POT) doped with perchloric (HClO₄) acid was studied by thermogravimetric analysis (TG) and differential thermal analysis (DTA) under non-isothermal conditions. Molecular mechanics (MM) calculations suggest that the optimal geometric structure (OMG) of the HClO₄-doped POT is at least four orders of magnitude more stable than the molecular geometric (MG) structure. These calculations indicate that the potential energy (PE/kJ mol⁻¹) of the OMG is about four (1.09·10⁴) orders of magnitude lower than the MG structure of the same matrix. The empirical formula of the doped polymer is best represented by [POT-2HClO₄·2H₂O]_n as substantiate by elemental analysis and MM calculations. The full polymer decomposition and degradation were found to occur in three stages during the temperature increase. The decomposition activation energy (E _d) of HClO₄-doped POT matrix was calculated by employing different approximations. The heating rate (α) of the decomposition and the frequency factor (K _o) were calculated. A number of equations were used to evaluate the kinetic parameters. The mechanism of the degradation of the conducting polymer is explained on the basis of their kinetic parameters. A remarkable heating rate dependence of the decomposition rate was observed.     

Thermoanalytical evaluation of readily available reference polymers

A commercial set of polymers has been characterized by TG-DTA, DSC, TMA, FTIR spectroscopy and X-ray diffraction analysis (XRD). Thermal and mechanical stability, as well as the polymer glass transition temperature,T _g, and melt temperature,T _m, have been documented. There is a good correlation between measuredT _g andT _m values and published data. The degree of polymer crystallinity for polyethylene has been verified by XRD. The credibility and stability of these reference polymers is based on a comparison of their thermal properties, over a wide range of temperatures from two versions of a reference set, published in 1979 (A) and 1994 (B). The thermal properties and crystallinity of these polymers have stood the test of time and are reliable, readily available and consistent.     

Proton‐conducting polymers based on benzimidazoles and sulfonated benzimidazoles

A sulfonated derivative of polybenzimidazole is reported, and its properties are analyzed in comparison with related polybenzimidazole proton‐conducting materials. Poly(2,5‐benzimidazole), poly(m‐phenylenebenzobisimidazole), and poly[m‐(5‐sulfo)‐phenylenebenzobisimidazole] were prepared by condensation of the corresponding monomers in polyphosphoric acid. Several adducts of these polymers with phosphoric acid were prepared. The resulting materials were characterized by chemical analysis, Fourier transform infrared spectroscopy, and thermogravimetric analysis; also, the dc conductivity of doped and undoped derivatives was measured. Similar to what has been observed for the commercial polybenzimidazole polymer (also examined here for comparison), the title polymers exhibit high thermal stability. Furthermore, their doping with phosphoric acid leads to a significant increase in conductivity from less than 10^?11 Scm^?1 for the undoped polymers to 10^?4 Scm^?1 (both at room temperature) for their acid‐loaded derivatives. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3703–3710, 2002     

Thermooxidative degradation of an unsaturated polyester resin

The results of non-isothermal kinetic analysis of the thermooxidative degradation in air and oxygen of an unsaturated polyester resin are presented. It has been shown that the thermooxidative degradation in oxygen occurs at lower temperatures than the thermooxidative degradation in air. The kinetic parameters of the thermooxidative degradation depend on the heating rate and the oxygen pressure. Two straight lines of InAvs. E (A is the preexponential factor andE is the activation energy), characteristic for the compensation effect, have been obtained for the thermooxidative degradation in air and in oxygen respectively. The difference between the intercepts of these straight lines can be explained by dependence of the pre-exponential factor on the oxygen pressure.     

Biodegradable polymers; Part II. Thermal degradation of biodegradable plastics cross-linked from formaldehyde-soy protein concentrate

Soy protein concentrate, a biodegradable renewable resource agricultural biopolymer, has been cross-linked with formaldehyde for better processing material. Thermogravimetric analysis of the biopolymer has been followed using a computer analysis method, Lotus package, developed by us for assigning the degradation mechanism. A number of equations have been used to evaluate the kinetic parameters. The mechanism of degradation of the biopolymer is explained on the basis of the kinetic parameters.     

Degree of branching of the hyperbranched polymers resulted from ab<Subscript>2</Subscript> polycondensation with substitution effect

The analytical expressions of the various structural units and the average degree of branching for the hyperbranched polymers resulted from AB₂ polycondensation with substitution effect were derived by the kinetic mechanism.The reactivity difference between the B group in linear unit and that in terminal group has great effect on the molecular parameters of the products obtained.The concentration of terminal units has a maximum with the increase of the conversion of A groups（x）.The higher the reactivity ratio（r） of linear B group to branched one is,the later the maximum appears and the larger it is.The degree of branching of the hyperbranched polymers obtained is controllable by adjusting the parameters of r and x,which increases with increasing both x and r.     

Enhanced general analytical equation for the kinetics of the thermal degradation of poly(lactic acid) driven by random scission

An enhanced general analytical equation has been developed in order to evaluate the kinetic parameters of the thermal degradation of poly(lactic acid) (PLA) at various linear heating rates and at constant rate conditions. This improvement consisted of replacing the n-order conversion function by a modified form of the Sestak-Berggren equation f(α) = c(1?α)ⁿα^m, which led to better adjustment of experimental data, and also adequately represented the conventional mechanisms for solid-state processes. The kinetic parameters so obtained have been compared to those determined by conventional differential and isoconversional methods. Given that the thermal degradation of PLA has been argued to be caused by random chain scission reactions of ester groups, the conversion function (α) = 2(α^1/2?α), corresponding to a random scission mechanism, has been tested.