Mechanisms of thermal degradation of polystyrene,polymethacrylonitrile, and their copolymers on flash pyrolysis

The mechanism of thermal degradation of homopolymers of styrene (St) and methacrylonitrile (MAN) and their copolymers was investigated theoretically and experimentally by the pyrolysis gas chromatography using a Curie-point pyrolyzer. Poly(St-co-MAN)s generate dimers and trimers as well as monomers by flash pyrolysis. Parameter α was proposed to account for the competition between the back-biting reaction and depolymerization. The back-biting parameter α is defined as the ratio of rate constants, α = k_bb/k_dp, where k_bb is the rate constant for the back-biting reaction and k_dp is that for depolymerization. The back-biting process is followed by β-scission, where dimer and trimer are generated, and directly correlated with the C—H bond dissociation energies in the polymer chain. Using the back-biting parameter α, where 1/α is equal to the zip length n in depolymerization, the boundary effect for the difference of monomer yields from the homopolymers of St and MAN and their copolymers is well explained. The calculated values of boundary effect parameters, β_St and β_MAN, agreed well with the experimental results. It was found that thermal degradation mechanisms of homo- and copolymers of vinyl compounds can be analyzed comprehensively using the back-biting parameter α and the boundary effect parameter β. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2315–2330, 1998     

Structural stability of poly(1-propyne) dimers and trimers

The relative thermodynamic energies of the poly(1-propyne) dimers and trimers show that both the conjugation and steric forces play an important role on the structural stability of these molecular systems. The two 1,4-disubstituted butenyne cis and trans dimers are predicted to be practically the same in energy, whereas the 2,4-disubstituted butenyne dimer is of relatively lower thermodynamic stability. The trimers, cis-trans (structure 4) and trans-trans (structure 10), are calculated to be relatively stable, and thus it is more likely that the polymer formation is based on these two trimers with the tail-head-tail-head addition. © 1996 John Wiley & Sons, Inc.     

Direct pyrolysis mass spectrometry studies on thermal degradation characteristics of poly(phenylene vinylene) with well-defined PSt side chains

Thermal degradation characteristics of a new macromonomer polystyrene with central 4,4′-dicarbaldehyde terphenyl moieties and poly(phenylene vinylene) with well-defined polystyrene (PPV/PSt) as lateral substituents were investigated via direct pyrolysis mass spectrometry. A slight increase in thermal stability of PSt was detected for (PPV/PSt) and attributed to higher thermal stability of PPV backbone. It was almost impossible to differentiate products due to the decomposition of PPV backbone from those produced by degradation of PSt.     

Compatibility and thermal properties of poly(3‐hydroxybutyrate)/poly(glycidyl methacrylate) blends

Poly(3‐hydroxybutyrate) (PHB)/poly(glycidyl methacrylate) (PGMA) blends were prepared by a solution‐precipitation procedure. The compatibility and thermal decomposition behavior of the PHB/PGMA blends was studied with differential scanning calorimetry, thermogravimetric analysis, and differential thermal analysis (DTA). The blends were immiscible in the as‐blended state, but for the blends with PGMA contents of 50 wt % or more, the compatibility was dramatically changed after 1 min of annealing at 200 °C. In addition, PHB/PGMA blends showed higher thermal stability, as measured by maximum decomposition temperatures and residual weight during thermal degradation. This was probably due to crosslinking reactions of the epoxide groups in the PGMA component with the carboxyl chain ends of PHB fragments during the degradation process, and the occurrence of such reactions can be assigned to the exothermic peaks in the DTA thermograms. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 351–358, 2002     

Radiation effects on the thermal degradation of poly(vinyl chloride) and poly(vinyl alcohol)

Radiation effects on the formation of conjugated double bonds in the thermal degradation of poly(vinyl chloride) (PVC) and poly(vinyl alcohol) (PVA) were investigated. Thin films of PVC and PVA were either irradiated with γ-rays at ambient temperature (pre-irradiation) and then subjected to thermal treatment, or irradiated at elevated temperatures (in situ irradiation). An extensive enhancement of the thermal degradation was observed for the pre-irradiation of the PVC films, which was more effective than the effect of the in situ irradiation at the same absorption dose. For the PVA degradation, however, the effect of the in situ irradiation was larger than that of the pre-irradiation. The results were explained and related mechanisms were discussed based on radiation-induced chemical reactions and their individual contributions to the thermal degradation behaviors of the two polymers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 3089–3095, 1998     

气相色谱法探究聚醚醚酮的热降解及热氧化降解（英文）

Poly(ether ether ketone)(PEEK)was synthesized via polycondensation of hydroquinone with 4,4′-difluorobenzophenone at 320℃for 5 h.Thermal and thermo-oxidative degradation of PEEK was studied over a wide range of temperatures.In an inert medium,decomposition of the polymer occurred in one stage,with the formation of a coke residue accounting for approximately 50%of the original polymer mass.In air,the mass loss curve exhibited two distinct stages.The first stage involved breakdown of the main polymer chain,the speed of which indicated a radical chain failure mechanism.In the second stage,the rate of mass loss clearly decreased,indicating a transition from the radical chain failure mechanism to simple combustion reactions(wherein the polymer combusted completely).To further investigate the nature of the processes occurring during the pyrolysis of PEEK,the investigations were carried out using gas chromatograph under isothermal conditions.It was concluded that during thermal degradation,the decomposition of the polymer starts with the rupture of ketone and ether bonds and proceeds to destruction of the benzene ring at higher temperatures,which is accompanied by the formation of H2O and CH4.Above 500℃,the polymer degradation further involved thermohydrolysis.The thermo-oxidation of PEEK,which was accompanied mainly by the formation ofH2,was noticeable beginning at 325℃.The total yield of the latter indicated oxidation of fragments of the benzene ring.     

Organocatalytic depolymerization of poly(ethylene terephthalate)

We describe the organocatalytic depolymerization of poly(ethylene terephthalate) (PET), using a commercially available guanidine catalyst, 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (TBD). Postconsumer PET beverage bottles were used and processed with 1.0 mol % (0.7 wt %) of TBD and excess amount of ethylene glycol (EG) at 190 °C for 3.5 hours under atmospheric pressure to give bis(2‐hydroxyethyl) terephthalate (BHET) in 78% isolated yield. The catalyst efficiency was comparable to other metal acetate/alkoxide catalysts that are commonly used for depolymerization of PET. The BHET content in the glycolysis product was subject to the reagent loading. This catalyst influenced the rate of the depolymerization as well as the effective process temperature. We also demonstrated the recycling of the catalyst and the excess EG for more than 5 cycles. Computational and experimental studies showed that both TBD and EG activate PET through hydrogen bond formation/activation to facilitate this reaction. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Effects of nano nickel powders addition on flash pyrolysis of poly(ethylene glycol)

Pure PEG and the mixture of PEG and nano nickel powders (PEG/n-Ni) were pyrolyzed at 500 °C for 5 min in N₂ atmosphere. GC/MS and FTIR were employed to detect the volatile products. Some important regularity in the mass spectra of the PEG pyrolysis products was discovered, and 11 series of PEG pyrolysis products were identified. The experimental results show that the nano Ni powders evidently change the relative contents of each products series. The statistical results of the ratio of C-O cleavage to C-C cleavage, as well as the ratio of hydrogenation to dehydrogenation, indicate that nano Ni powders have remarkable effects on the bonds cleavage and free radicals annihilation. The process of hydrogenolysis and hydrogenation were propounded to explain the effects of nano Ni addition on PEG flash pyrolysis.     

反气相色谱法测定聚环己基丙烯酸甲酯的热力学性质（英文）

In this work,some thermodynamic properties of poly(cyclohexyl methacrylate)were studied by inverse gas chromatography(IGC).For this purpose,the polymeric substance was coated on Chromosorb W and which was filled into a glass column.The retention times(tr)of the probes were determined from the interactions of poly(cyclohexyl methacrylate)with n-pentane,n-hexane,n-heptane,n-octane,n-decane,methanol,ethanol,2-propanol,butanol,acetone,ethyl methyl ketone,benzene,toluene and o-xylene by IGC technique.Then,the specific volume(V0g)was determined for each probe molecule.By using(1/T;ln V0g)graphics,the glass transition temperature of poly(cyclohexyl methacrylate)was found to be 373 K.The adsorption heat under the glass transition temperature(ΔHa),and partial molar heat of sorption above the glass transition(ΔHS1),partial molar free energy of sorption(ΔGS1)and partial molar entropy of sorption(ΔSS1)belonging to sorption for every probe were calculated.The partial molar heat of mixing at infinite dilution(ΔH∞1),partial molar free energy of mixing at infinite dilution(ΔG∞1),Flory-Huggins interaction parameter(χ∞12)and weight fraction activity coefficient(a1/w1)∞values of polymer-solute systems were calculated at different column temperatures.The solubility parameters(δ2)of the polymer were obtained by IGC technique.     

Thermal oxidation of blends of poly(ethylene oxide) and poly(methyl methacrylate)

Thermal oxidation of poly(ethylene oxide) (PEO) and its blends with poly(methyl methacrylate) (PMMA) were studied using oxygen uptake measurements. The rates of oxidation and maximum oxygen uptake contents were reduced as the content of PMMA was increased in the blends. The results were indicative of a stabilizing effect by PMMA on the oxidation of PEO. The oxidation reaction at 140°C was stopped at various stages and PMMA was separated from PEO and its molecular weights were measured by gel permeation chromatography (GPC). The decrease in the number-average molecular weight of PMMA was larger as the content of PEO increased in the blends. The visual appearance of the films suggested that phase separation did not occur after thermal oxidation. The activation energy for the rates of oxidation in the blends was slightly increased compared to pure PEO. © 1992 John Wiley & Sons, Inc.     

Monomer-isomerization radical polymerization of di-tert-butyl maleate and preparation of poly(fumaric acid) via pyrolysis

Di-tert-butyl maleate (DtBM) did not polymerize with 2,2′-azobis(isobutyronitrile) as a radical initiator, but DtBM easily homopolymerized via a monomer-isomerization radical polymerization mechanism to give a high molecular weight polymer when morpholine was added into the polymerization system as an isomerization catalyst. The feature of the monomer-isomerization polymerization of DtBM was investigated in detail. The polymer obtained was confirmed to consist of a poly(tert-butoxycarbonylmethylene) structure similar to that from di-tert-butyl fumarate. Subsequent pyrolysis of the resulting polymer at 180°C is a useful route to synthesis of a high molecular weight poly(fumaric acid). © 1993 John Wiley & Sons, Inc.     

The microstructure and macrostructure of sulfonated poly(ethylene terethphalate) fibers

The effects of fiber-forming processes on the microstructure and macrostructure and overall orientation in sulfonated poly(ethylene terephthalate) (SPET) fibers are reported. The processing parameters examined include drawing, crimping, relaxing, and annealing. Drawing and annealing cause changes in both the crystalline structure and molecular packing in the noncrystalline regions, while crimping and relaxing appear to affect only the noncrystalline regions. A bimodal melting endotherm was observed for the SPET fibers. Experimental data suggest the low-temperature endotherm of the SPET fibers originates from melting of the crystalline structure formed on drawing, and that the high-temperature endotherm results from melting the heat-induced crystals formed during fiber processing and/or thermal analysis. Compared to the PET fibers, the SPET chains in the undrawn fibers appear to have higher mobility, are easier to crystallize, and form smaller crystals upon drawing as well as DTA heating. At the crimped stage, the SPET fibers have higher overall molecular packing but lower overall orientation than the PET fibers. The differences in physical and thermal properties between the analogous SPET and PET fibers are related to their different responses to processing variations because of molecular weight and sidegroup effects. © 1993 John Wiley & Sons, Inc.     

Influence of structural factors on degradation product formation: Primary pyrolysis products of poly(acyl sulfides) investigated by direct pyrolysis mass spectrometry

Thermal degradation of two poly(acyl sulfide) polymers, poly(adipoyl sulfide) (PADS) and poly(terephthaloyl sulfide) (PTS) was investigated by direct pyrolysis mass spectrometry (DPMS). The structures of pyrolysis products detected in the DPMS analysis of both PADS and PTS indicate that the thermal degradation takes place mainly through a loss of carbon monoxide and carbonyl oxysulfide leading to the formation of cyclics. In the case of PADS, linear products with thioacid end groups were formed through hydrogen transfer reactions. In the case of PTS, almost equal proportions of linear products with phenyl end groups and cyclic products were formed. The mechanism of formation of degradation products has also been addressed.     

Primary thermal degradation processes occurring in poly(phenylenesulfide) investigated by direct pyrolysis–mass spectrometry

The thermal degradation Processes which occur in poly(phenylenesulfide) (PPS) have been studied by direct pyrolysis-mass spectrometry (DPMS). The structure of the compounds evolved in the overall temperature range of PPS decomposition (400–700°C) suggests the occurrence of several thermal decomposition steps. At the onset of the thermal degradation (430–450°C) this polymer decomposes with the formation of cyclic oligomers, generated by a simple cylization mechanism either initiated at the—SH end groups or by the exchange between the inner sulfur atoms along the polymer chain. At higher temperature (> 500°C) another decomposition reaction takes over with the formation of aromatic linear thiols. The formation of thiodibenzofuran units by a subsequent dehydrogenation reaction occurs in the temperature range of 550–650°C; in fact, pyrolysis products with a quasi-ladder structure have also been detected. Ultimately, above 600°C, extrusion of sulfur from the pyrolysis residue occurs with the maximum evolution at the end of decomposition (about 700°C). It appears, therefore, that the residue obtained at high temperature tends to have a crosslinked graphite-like structure from which the bonded sulfur is extruded. © 1994 John Wiley & Sons, Inc.     

Thermal stability of poly(styrene) containing no head-to-head units

General purpose poly(styrene) prepared by conventional radical techniques contains a head-to-head unit as a consequence of polymerization termination by radical coupling. As has been previously demonstrated, thermal stress promotes homolysis of the bond linking the head-to-head components. The macroradicals generated depolymerize rapidly to generate styrene monomer. This decomposition during processing can lead to finished articles containing objectionable levels of styrene monomer, particularly for food packaging applications in which even low levels of monomer can promote objectionable taste and aroma. Polymer containing no head-to-head units should not be prone to this facile decomposition. In this instance, poly(styrene) has been prepared by nitroxyl-mediated polymerization of styrene monomer followed by reductive removal of nitroxyl end groups. Polymer prepared in this manner contains no head-to-head units and displays thermal stability much greater than that observed for conventional poly(styrene). A direct comparison of the stability for the two polymers is readily available by thermogravimetric techniques. A quantitative reflection of the difference in stability is available from the rate constants for the respective decomposition.     

Synthesis and characterization of new poly(N-1-adamantylmaleimide) and poly(N-1-diamantylmaleimide)

N-l-Diamantylmaleimide was synthesized by reaction of maleic anhydride with 1-aminodiamantane, followed by dehydration with acetic anhydride and sodium acetate. Poly(N-1-adamantylmaleimide) ( IIa ) and poly(N-l-diamantylmaleimide) ( IIb ) were polymerized using 2,2′-azobisisobutyronitrile (AIBN) as an initiator under different experimental conditions such as various initiator concentrations, solvents, polymerization temperatures, and polymerization times. Polymerizations of N-l-adamantylmaleimide in benzene at 60°C or in bulk gave polymers with molecular weights (2000–9500). The experimental results indicated that the propagation may be interrupted by steric hindrance of bulky and rigid substituents such as the adamantyl or diamantyl groups. In addition, the effect of chain transfer to monomer contributes to the relatively low activation energy. The glass transition temperatures of Ia and Ib were 204 and 216°C, respectively. The temperatures at 5% weight loss of the polymers IIa and IIb were above 412°C. © 1996 John Wiley & Sons, Inc.     

Thermal properties of poly(anthranilic acid) (PANA) and humidity-sensitive composites derived from heat-treated PANA and poly(vinyl alcohol)

Thermal conversion of poly(anthranilic acid) (PANA) to polyaniline (PAn) has been studied by means of thermogravimetric/mass (TG/MS) and Fourier transform infrared (FTIR) spectroscopy. The electrical conductivity of the chemically prepared PANA was 3.5 × 10⁻² S/cm, which is caused by the self-doping of the polaronic nitrogen atom interacting with the ionized carboxyl group ( COO⁻). The heat-treated PANA can be assumed to be identical to an emeraldine base of PAn. The pyrolysis of PANA proceeded through the decarboxylation at two stages from carboxyl ( COOH) and ionized carboxyl groups, which occurred at about 170 and 230 °C, respectively. PANA–SA, which was prepared by treating PANA at 250 °C and then doping with an external protonic acid at room temperature, showed a considerably high conductivity (6.2 S/cm). The composite consisting of PANA–SA and poly(vinyl alcohol) was very sensitive to the environmental humidity. The logarithm of electrical conductivity of this composite was proportional to the relative humidity covering more than five orders of magnitude, and the change in conductivity extended from 4.2 × 10⁻⁵ to 10 S/cm upon the humidity variation from 14 to 91%. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4458–4465, 1999     

Miscibility and surface characterization of a poly(vinylidene fluoride)‐poly(vinyl methyl ketone) blend by inverse gas chromatography

The miscibility of blends of semicrystalline poly(vinylidene fluoride)(PVF₂) and poly(vinyl methyl ketone) (PVMK) along with surface characterization were investigated using the inverse gas chromatography method (IGC), over a range of blend compositions and temperatures. Three chemically different families, alkanes, acetates, and alcohols, were utilized for this study. The values of the PVF₂‐PVMK interaction parameters were found to be slightly positive for most of the solutes used, although some degree of miscibility was found at all compositions. Miscibility was greatest at a 50:50 w/w composition of the blend. The interaction parameters obtained from IGC are in excellent agreement with those obtained using calorimetry on the same blends. The calculated molar heat of sorption of alkanes, acetates, and alcohols into the blend layer reveal the impact of the combination of dispersive and hydrogen bonding forces on the interaction of solutes with the blend's backbone. The dispersive component of the surface energy was found to range from 18.70–64.30 mJ/m² in the temperature range of 82–163 °C. A comparison of the blend's surface energy with that of mercury and other polymers is given. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1155–1166, 2000     

典型城市固体废弃物热解动力学机理研究

利用热重（TGA）技术研究了城市固体废弃物中塑料橡胶类、木质纤维素类、织物类和厨余类四大类可燃组分中七种典型固体废弃物热解反应过程。实验结果表明,塑料类和织物类最难热解,厨余类组分最易热解;采用Freeman-Carroll法对七种典型固体废弃物热解进行数据处理,从20种常用的固相反应机制函数中遴选出最优解,利用优化的数学函数和动力学参数建立动力学模型,结果表明,PE和羊毛线热解主要反应阶段的最优固相反应模型是球形相界面反应模型;橡胶粉、杨树枝热解反应模型遵循化学反应规律;米饭和本白棉布热解曲线遵循幂函数法则;白菜的最优模型是三维扩散模型。     

Characterization and degradation of poly(methylphenylsiloxane)–poly(methyl methacrylate) interpenetrating polymer networks

Poly(methylphenylsiloxane)–poly(methyl methacrylate) interpenetrating polymer networks (PMPS–PMMA IPNs) were prepared by in situ sequential condensation of poly(methylphenylsiloxane) with tetramethyl orthosilicate and polymerization of methyl methacrylate. PMPS–PMMA IPNs were characterized by infrared (IR), differential scanning calorimetry (DSC), and ²⁹Si and ¹³C nuclear magnetic resonance (NMR). The mobility of PMPS segments in IPNs, investigated by proton spin–spin relaxation T₂ measurements, is seriously restricted. The PMPS networks have influence on the average activation energy E_a,av of MMA segments in thermal degradation at initial conversion. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1717–1724, 1999