Thermal analysis of styrene–alkyl methacrylate polymers. II. Thermogravimetric kinetics

The thermal stability and degradation kinetics of several polystyrenes and styrene–alkyl methacrylate copolymers and terpolymers with a number-average molecular weight (M?_n) of 6000–250,000 g/mole have been studied using dynamic thermogravimetry (TG). The degradation kinetics of each polymer sample have been successfully attributed to a sample first-order reaction expression. The results indicate that the thermal stability and degradation kinetics of the polymers are independent of the size of the molecules within the molecular weight range investigated. The steric hindrance effects of the pendent groups appear to be responsible for the improved thermal stability and resistance of C? C bond scission in the styrene–alkyl methacrylate copolymers and terpolymers.     

Synthesis and characterization of ethylene-xylene-based polysulfide block-copolymers using the interfacial polymerization method

Copolymers of linear and aromatic polysulfide blocks are synthesized using interfacial polymerization of dichloro-xylene-based aromatic and ethylene-dichloride-based non-aromatic organic monomers. Synthesized copolymers consist of poly(ethylene sulfide) as well as ploy (xylene sulfide) blocks. Fascinating properties of linear and aromatic polysulfide species are gathered in the structure of synthesized polysulfide copolymers. Ethylene dichloride and α,α′-dichloro-p-xylene are used as the non-aromatic and aromatic organic monomers, respectively. To investigate the influences of sulfur contents in the backbone of the polymer on the thermal stability of synthesized copolymers, poly(ethylene-xylene disulfide) (PEXDS), poly(ethylene-xylene trisulfide) (PEXTRS) and poly(ethylene-xylene tetrasulfide) (PEXTS) copolymers are synthesized using, respectively, sodium disulfide, sodium trisulfide and sodium tetrasulfide, as aqueous monomers. Compared to both linear and nonlinear homopolymers, synthesized copolymers exhibit improved thermal stability. Moreover, the thermal degradation temperatures of synthesized copolymers improve by decreasing the number of sulfur atoms in the backbone of copolymers. These results reveal that thermal degradation of polysulfide copolymers can be tailored by controlling the polysulfide chain’s sulfur contents. Structural characteristics of synthesized polysulfide copolymers are also investigated using Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy and X-ray diffraction analysis.     

Thermo-oxidative degradation of heterophasic ethylene-propylene copolymers and their fractions

The thermo-oxidative degradation behaviour of heterophasic ethylene-propylene copolymers and their fractions is discussed and the results are compared with those for the corresponding homopolymers. The most informative results were obtained when a small reactive species produced in the degradation was treated with reactive gases. The extent of thermal degradation was monitored by Fourier transform infrared spectroscopy. The kinetics of oxygen absorption have also been studied at 140° C. Oxygen deficiency is manifested in the formation of diffusion-limited products from ethylene-propylene copolymer samples.     

Thermal degradation of butadiene–styrene-based rubber

Thermal degradation of some commerically available rubber based on butadiene–styrene copolymers are studies as a function of composition, temperature, and heating periods using photoacoustic spectroscopy (PAS) technique. It was found that random copolymers are more degradable than block copolymers and that the latter is more degradable than alternate copolymers. Mechanistic schemes leading to the thermal degradation of these synthetic rubbers are given together with a qualitative explanation of the relation between their composition and their thermal stabilites.     

Structure–property relationship in copolymers of methacrylic acid esters. I. Thermal behavior

This article describes the synthesis and thermal characterization of copolymers of methyl methacrylate (MMA) and alkyl methacrylates. The copolymerization was carried out using different mol fractions (0.05–0.25) of alkyl methacrylates, i.e., octyl methacrylate (OMA)/decyl methacrylate (DMA)/lauryl methacrylate (LMA)/stearyl methacrylate (SMA), in the initial feed at 80°C. The copolymer composition was determined from ¹H-NMR. The thermal stability of the copolymers was investigated by thermogravimetric analysis and pyrolysis gas chromatography. A two/three-step degradation was observed in the copolymer samples. The monomers were the major product of degradation in most of the copolymers except in SMA/MMA copolymers where the product of side-group elimination was also observed. An attempt was also made to determine the yield of the monomers during degradation and then to evaluate the copolymer composition. © 1994 John Wiley & Sons, Inc.     

Thermal oxidative degradation kinetics and thermal properties of poly(ethylene terephthalate) modified with poly(lactic acid)

The thermal oxidative degradation kinetics of poly(ethylene terephthalate) (PET) copolymers modified with poly(lactic acid) (PLA) were investigated with thermogravimetric analyzer (TGA). The thermal properties of the modified products were also determined by differential scanning calorimeter (DSC) technique. Waste PET (P100) obtained from postconsumer water bottles was modified with a low‐molecular‐weight PLA. The PET/PLA weight ratio was 90/10 (P90) and 50/50 (P50) in the modified samples. The thermal oxidative degradation kinetics of the modified samples was compared with those of PET (P100). The segmented block and/or random copolymer structure of the modified samples formed by a transesterification reaction between the PLA and PET units in solution and the length of the aliphatic and aromatic blocks were found to have a great effect on the degradation behavior. On the basis of the results of the degradation kinetics determined by Kissinger method, the degradation rate of the samples decreased in the order of P50 > P90 > P100, depending on the amount of PLA in the copolymer structure. However, the degradation activation energies (E_A) of the samples decreased in the order of P100 > P90 > P50. It was concluded that the degradation rate and mechanism were affected significantly by the incorporation of PLA into the copolymer structure. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermal degradation of polymer mixtures. I. Degradation of polystyrene–poly(methyl methacrylate) mixtures and a comparison with the degradation of styrene–methyl methacrylate copolymers

The degradation behavior of mixtures of polystyrene and poly(methyl methacrylate) in the form of thin films cast from a solution containing both polymers has been compared with that of the individual polymers and of copolymers of the same monomer pair by means of thermal volatilization analysis (TVA) together with product analysis by gas-liquid chromatography determinations of the molecular weight of the solid polymer residues. The results indicate no interaction between the polymers when degraded together. The polymer mixtures are readily distinguished from copolymers of the same overall composition by TVA.     

Activity and Reactivity of Carbon Formed by the Thermal Degradation of Poly(vinyl butyral) in Alumina Pellets

This paper discusses the kinetics of the oxidation of carbon formed by the thermal degradation of poly (vinyl butyral) (PVB) in alumina pellets. The kinetics, studied in a flow reactor using wet nitrogen as the oxidant, followed zero-order kinetics. The carbon was found to be very reactive, and it possibly was a form of Dent carbon. The activity of this carbon compared with graphite in alumina pellets showed that the carbon formed by the thermal degradation of PVB to be 4 to 6 times more active than graphite. The total organic content of the pellets was varied from 0% to 15% and the kinetics was studied in the temperature range of 873 to 1073 K. Activation energies were expressed as a function of the weight percent of carbon in the pellet. Experimental data with two particle sizes of alumina gave different activation energies.     

Development of epoxy-cyanate ester-clay nanocomposites offering enhanced thermally stability

The preparation and characterization of blends of a series of dicyanate monomers such as 2,2′-bis(4-cyanatophenyl) propane (DCDPP), bis-4-cyanato-biphenyl (DCBP), bis-4-cyanatonaphthalene (DCN), 3,3′-bis(4-cyanatophenyl)sulphide (DCTDP), 3,3′-bis(4-cyanatophenyl)sulphone (DCDPS), and the diglycidyl ether of bisphenol A are reported. These copolymers are combined with a montmorillionite nanoclay and both epoxy-cyanate blends and epoxy-cyanate blends-nanoclay composites are all analyzed for thermal stability, thermal degradation kinetics, flame retardancy, and impact strength. The nanocomposites are further characterized by X-ray diffraction and SEM to determine morphological features, from which structure–property relationships are determined. Dispersion of the nanoclay is of paramount importance, but its inclusion serves to improve char yield and impact strength, when this is achieved. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47754.     

Effect of soft segment on degradation kinetics in polyethylene glycol/poly(l-lactide) block copolymers

Summary The hydrolytic degradation of polyethylene glycol(PEG)/poly (L-lactide)(PLLA) copolymers with various PEG wt% contents at 37°C and pH=7 was studied by differential scanning calorimetry(DSC) and gel permeation chromatography(GPC). The effect of PEG contents in PEG/PLLA copolymers on the crystalline morphology and hydrolytic degradation rate was investigated. Due to the hydrophilic PEG segments in PEG/PLLA copolymers, the exothermic recrystallization and the shoulder portion of melting endotherm appear immediately following the hydrolysis of copolymers. Moreover, after a period of hydrolysis of 100 h. the molecular weight distribution turn to a bimodal shape from a unimodal in the original, and the polydispersity becomes greater with a value from 1.5 up to 5, which are not observed for PLLA homopolymer. The rate constants of hydrolysis for the first-order auto-catalytic kinetics, increase with the PEG content over 0 to 18.3 wt%, ranging from 1 to 6x10^-4hr^-1.     

Particular thermal properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) oligomers

Telechelic hydroxylated poly(3-hydroxybutyrate-co-3-hydroxyvalerate)s (PHBV-diols) were synthesized by transesterification with ethylene glycol, which could be used as the macromonomers for synthesis of block copolymers. PHBV-diols owned particular thermal properties. PHBV-diols had much lower the melting temperatures (T _m s) and better thermal stability than original PHBV. With the decrease of molecular weight, T _m s of PHBV-diols decreased gradually and maximum degradation temperatures (T _max s) increased gradually. T _max -T _m of PHBV-diol could increase by 57.9 °C in comparison with original PHBV. It was meaningful that PHBV block in the block copolymers based on PHBV-diol owned the good thermal stability and low melting temperature of its precursor PHBV-diol, which widened greatly the melt-processing window of PHBV. In addition, thermal degradation kinetics was studied by Ozawa method, the integration method and Kissinger method. The results showed that the thermal degradation of original PHBV and PHBV-diols proceeded by at least two steps including a random degradation process and subsequent thermal degradation process due to the auto-accelerated degradation reaction.     

Determination of the kinetic parameters of the thermal oxidative degradation of styrene/butadiene copolymers

The intensity of the thermal oxidation has been followed through kinetic parameters. In styrene/butadiene copolymers, soft polybutadiene phase (PB) and hard polystyrene phase (PS) have different sensibilities to thermal degradation. The thermal oxidative stability of high-impact polystyrene (PS-HI), styrene/butadiene/styrene block copolymers (SBS), and PS-HI + SBS blends were investigated by isothermal DSC analysis. The kinetic parameters of the thermal oxidative degradative process: the reaction rate constants, the reaction orders and the activation energies have been determined. The total area under the exothermic curve was used to calculate the isothermal heats of degradation. The conversion (α) and the rate of the thermal oxidative degradation (dα/dt) have been derivated. The experimental data have been tested with a kinetic model for autocatalytic reactions: dα/dt = k α^m (1 ? α)ⁿ. Activation energies have been determined from the Arrhenius equation and the order of the thermal oxidative stability evaluated. The extent of agreement of the experimental data with the autocatalytic model is discussed.     

Some aspects of the thermal stability of poly(alkyl itaconic acid esters)

The thermal stability of members of several series of polyitaconates has been assessed using thermogravimetric and thermal volatilisation techniques. From these data general degradation patterns have been established. The poly (di-n-alkyl itaconates) are stable up to 570K before chain breakdown occurs. The poly(mono-n-alkyl itaconates) are less stable and undergo a dehydration/de-esterification reaction at 430K which results in the formation of anhydride structures. This reaction can be suppressed by the formation of the salts. In the copolymers, salt formation also leads to increased stability but the range of copolymers studied was too restricted to draw general conclusions about their thermal behaviour.     

Thermal and photodegradation of vinyl chloride/vinyl bromide copolymers

Vinyl chloride/vinyl bromide (VC/VBr) copolymers have been synthesized by radical copolymerization in bulk. Conversion increases and molecular weight of the copolymers decreases with increasing VBr in the feed. This indicates that VBr is a chain transfer agent in VC/VBr copolymerization systems. In accordance with the lower thermal stability of the vinylbromide homopolymer (PVBr), thermal degradation experiments show that the stability of the copolymers significantly decreases with increasing VBr content. It has been found that the initial rate of dehydrohalogenation is an exponential function of VBr content during thermal degradation of VC/VBr copolymers. In separate experiments, HBr evolved during degradation has been determined by a bromide selective electrode. The initial dehydrobromination rates of VC/VBr copolymers containing higher fractions of VBr are markedly higher than the initial dehydrochlorination rates. This clearly indicates the lower thermal stability of VBr monomer units compared with VC units. UV and visible spectra of degraded VC/VBr copolymers show that the absorption and the average length of polyenes are higher for samples with higher VBr content. Dehydrohalogenation curves obtained during photodegradation of VC/VBr copolymers show a faster initial phase followed by a slower stationary phase. The initial rate of dehydrohalogenation is higher for copolymers containing higher fractions of VBr, whereas these copolymers reach the slower stationary phases at lower extents of dehydrohalogenation.     

Studies of the degradation of copolymers of acrylonitrile and acrylamide in air at 200°C. Speculations on the role of the preoxidation step in carbon fiber formation

Fourier transform infrared (FT-IR) results of the thermal degradation of polyacrylonitrile (PAN) copolymers containing varying concentrations of acrylamide (AM) degraded at 200°C in air are presented. These results suggest that reactions other than intramolecular ring formation and intermolecular crosslinking are important. Products from reactions similar to those formed from autoxidation result in the formation of olefins and conjugated polyenes. It is speculated that these structures are precursors to the formation of fused ring systems necessary for high strength Carbon/Graphite ( ) fibers. A degradation scheme based on the IR results is advanced.     

Syntheses and characterization of poly(phenylene sulfide)–poly(ether sulfone) block copolymers

Poly(phenylene sulfide)-poly(ether sulfone) (PPS–PES) block copolymers were synthesized by polycondensation of chloro-terminated PPS oligomers and hydroxylic-terminated PES oligomers at atmospheric pressure. The structure and compositions of PPS–PES block copolymers were analyzed quantitatively by FTIR spectroscopy. It was found that the contents of PES in copolymers increase with the amount of PES in the added materials; however, the quantities of PES contents in copolymers are lower than its quantities in the added materials. The solubility, crystallization behavior, and thermal properties of PPS-PES block copolymers were studied through a solubility test, X-ray diffraction, DSC, and TGA. It was primarily proved that the copolymers have better solubility, lower crystallinity, and higher glass transition (T_g) than those of PPS. The nonisothermal crystallization kinetics and thermal decomposition kinetics of block copolymers were also studied; furthermore, the crystallization kinetic parameters and the activation energy of thermal decomposition were calculated. © 1996 John Wiley & Sons, Inc.     

Thermal analysis of polymers and copolymers derived from n-1-alkylitaconamic acids

Poly(N-1-alkylitaconamic acid) (PNAIA) containing ethyl, propyl, butyl, hexyl, octyl, decyl and dodecyl groups and random N-1-alkylitaconamic acid-co-styrene copolymers (NAIA-co-S) of three different compositions were selected and studied by dynamic thermogravimetric analysis (TGA). The thermal stability of homopolymers and copolymers depends on the structure of the NAIA and on the composition of the copolymer. The kinetic analysis of the degradation data shows that the thermal decomposition of the PNAIA can be described by zero order kinetic model. In the case of NAIA-co-S copolymers, the degradation process can be described by two different kinetic orders depending on the copolymer and on the composition. The thermal stability of the PNAIA in general increases as the length of the side chain increases. In the case of copolymers with styrene the relative thermal stability depends clearly on the composition and on the type of substituent in the side chain.     

Temperature-sensitive biodegradable mixed star-shaped block copolymers hydrogels for an injection application

3-arm star-shaped poly(d,l-lactic-co-glycolic acid)-b-methoxy poly(ethylene glycol)(3sPLGA-mPEG) and 4sPLGA-mPEG copolymers are synthesized via the arm-first method. A facile method to obtain a temperature-sensitive physical injectable hydrogel is found using simply mixing two 4sPLGA-mPEG block copolymers aqueous solutions individually with thermogelling property (sol-gel-sol transition) or using simply mixing an aqueous sol of a 3sPLGA-mPEG block copolymer with a precipitate of a similar 3sPLGA-mPEG copolymer but with a varying PLGA/mPEG block ratio. A dramatic tuning of the sol–gel transition temperature is conveniently achieved by merely changing mix ratios. The degradation of mixed 3sPLGA-mPEG hydrogel proceeds by hydrolysis of ester bonds followed by the erosion of gel in PBS solution at body temperature for nearly 50 days. The mass loss and reduction of molecular weight are detected with increasing degradation time, and the mix ratios are found to slightly influence the degradation profiles. MTT assay and histological observations are used to examine the mixed copolymer solution. Both in vitro and in vivo results illustrate acceptable biocompatibility of our mixed materials. Collectively, our results show that the mixed star-shaped PLGA-mPEG block copolymer is a promising candidate as a novel injectable gel.     

Water extraction and degradation of a sterically hindered phenolic antioxidant in polypropylene films

Water extraction of the sterically hindered phenolic antioxidant Irganox 1010 from three polypropylene based polymeric films has been studied in isothermal conditions at 40, 50 and 70 °C. The films made of isotactic polypropylene and two different heterophasic polypropylene/ethylene–propylene monomers copolymers (PP/EPM copolymers) were immersed in closed water baths under nitrogen atmosphere in order to minimise the oxidative process. The amounts of antioxidant that have left the films and are dissolved in the water bath have been monitored over time by HPLC analysis and faster extraction kinetics were observed from the polymers than from the homopolymer. No appreciable amounts of Irganox 1010 were found in the extraction water at any time, whereas its degradation by-products were found by LC/MS analysis in the extraction water.

The experimental extraction kinetics from the three polymers were compared with the theoretical curves based on the Fick's diffusion equations solved both for a semi-infinite (degradation reaction faster than extraction) and a finite system (no degradation reaction) and Irganox 1010 was demonstrated to be extracted by water from polypropylene based material faster than predictable only on the basis of the values of its coefficient of diffusion in the polymers and of partition between water and polymer.     

Thermal degradation of polymers. X. Thermal analysis studies on poly(p-N,N-dimethylaminostyrene) homopolymers and copolymers with styrene in nitrogen

Studies have been made on the effect of the molecular weight of p-N,N-dimethylaminostyrene homopolymers and the composition of its copolymers with styrene on the glass transition temperature. Comparative thermal degradation studies have been made on polystyrene and p-N,N-dimethylaminostyrene polymers by thermal analytical methods (TG, DTA, and DSC). The differences in thermal stability and overall thermal degradation behavior of the two systems are discussed in terms of the differences in their degradation mechanisms.