The Kinetics of Ester-Ester Exchange Reactions by Mass Spectrometry

The kinetics of ester-ester exchange reactions between poly(ethy1ene adipate) and poly(trimethy1ene adipate) have been studied by mass spectrometric techniques. Reactions were carried out in the absence of catalyst and solvent. Rate constants for the exchange reaction and corresponding Arrhenius parameters are given.     

Synthesis of polyester by means of polycondensation of diol ester and dicarboxylic acid ester through ester–ester exchange reaction

Based on our finding that the ester-ester exchange reaction between butyl benzoate and ethyl 4-phenylbenzoate in the presence of a metal alkoxide is faster than the ester-alcohol exchange reaction of butyl benzoate and ethanol, we investigated the synthesis of polyester through ester-ester exchange reaction under various conditions. The polycondensation of diol formate and methyl dicarboxylate in the presence of a catalytic amount of potassium tert-butoxide (^tBuOK) in diglyme at 120 °C under reduced pressure (90–100 Torr) afforded high-molecular-weight polyesters. Methyl dicarboxylate containing an amino group could be used for this polycondensation, although the corresponding diacid chloride containing an amino group was not isolable. The ester-ester exchange reaction could proceed even at the polyester backbone, and the reaction of poly(1,12-dodecamethylene isophthalate) ( PEs ₁ ) with poly(ε-caprolactone) (PCL) in the presence of ^tBuOK at 140 °C afforded a copolymer PEs ₁ -stat-PCL, the structure of which was confirmed by ¹³C NMR spectroscopy and DSC thermal analysis. A similar copolymer was also obtained by the polycondensation of dodecane-1,12-diol formate and dimethyl isophthalate in the presence of PCL and ^tBuOK at 120 °C under reduced pressure.     

Influence of the fire retardant,ammonium polyphosphate,on the thermal degradation of poly(methyl methacrylate)

The thermal degradation of ammonium polyphosphate (APP), a commercial fire retardant, and its blends with poly(methyl methacrylate) (PMMA) have been studied by thermal volatilization analysis (TVA) and the degradation products identified. APP degrades under vacuum in three stages. Initially it condenses to an ultraphosphate (<260°C) with release of ammonia and water. Fragmentation follows (260–370°C), giving high-boiling ammonium salts of phosphate fragments and further ammonia and water. The polyphosphoric acid (PPA) which remains then undergoes extensive Fragmentation (>370°C). In the presence of APP, the normal depolymerization of PMMA to monomer competes with degradation reactions which form high-boiling chain fragments, methanol, carbon monoxide, dimethyl-ether, carbon dioxide, hydrocarbons, and char. These additional reactions are initiated principally by the PPA. Intramolecular cyclization occurs, resulting in the formation of anhydride, and ester groups are eliminated, methanol and carbon monoxide being evolved. Further degradation of the modified polymer leads to the other volatile products and the char.     

The high-temperature degradation of poly(2,6-dimethyl-1,4-phenylene ether)

The thermal degradation of poly(2,6-dimethyl-1,4-phenylene ether) has been investigated to 1000°C in an inert atmosphere. X-ray diffraction, thermogravimetric analysis, and differential scanning calorimetry were employed to study the physical changes in the polymer, and vapor-phase chromatography, infrared spectroscopy, and mass spectrometric thermal analysis were used to elucidate the chemical aspects of the degradation process. It was found that degradation occurs in two steps: (1) a rapid exothermic process occurs between 430 and 500°C, leading to the evolution of phenolic products, water, and a black, highly crosslinked residue, and (2) a slower, char-forming process occurs above 500°C, characterized by the evolution of methane, carbon monoxide, and hydrogen. The chars formed in process 2 were found by x-ray analysis to be amorphous. The infrared spectrum of a sample heated to 510°C is nearly identical with that of the starting polymer, indicating that oxidative reactions are not important in the first process. The data for the low-temperature process are consistent with a thermal degradation scheme based on the radical-redistribution reaction of polyphenylene ethers and/or the degradation of o-benzylphenols formed by the thermal rearrangement of o-methyl diphenyl ethers. The char-forming process is best explained by simultaneous operation of the Szwarc mechanism of toluene pyrolysis, producing hydrogen and methane and reactions that cleave the aromatic rings and produce carbon monoxide.     

Chemical reactions occurring in the thermal treatment of PC/PMMA blends

The chemical reactions occurring in the thermal treatment of bisphenol-A polycarbonate (PC) and poly(methyl methacrylate) (PMMA) blends have been investigated by nuclear magnetic resonance (NMR), mass spectrometry (MS), size exclusion chromatography (SEC), and thermogravimetry (TG). Our results suggest that in the melt-mixing of PC/PMMA blends, at 230°C, no exchange reactions occur and that only the depolymerization reaction of PMMA has been observed. In the presence of an ester-exchange catalyst (SnOBu₂), an exchange reaction was found to occur at 230°C, but no trace of PC/PMMA graft copolymer has been observed. Instead, an exchange reaction between the monomer methyl methacrylate (MMA), generated in the unzipping of PMMA chains, and the carbonate groups of PC has been suggested. This is due to the diffusion of MMA at the interface or even into the PC domains, where it can react with PC producing low molar mass PC oligomers bearing methacrylate and methyl carbonate chain ends and leaving the undecomposed PMMA chains unaffected. The TG curves of PC/PMMA blends prepared by mechanical mixing and by casting from THF show two separated degradation steps corresponding to that of homopolymers. This behavior is different from that of a transparent film of PC/PMMA blend, obtained by solvent casting from DCB/CHCl₃, which shows a single degradation step indicating that the degradation rate of PC is increased by the presence of PMMA in the blend. The thermal degradation products obtained by DPMS of this blend consist of methyl methacrylate (MMA), cyclic carbonates arising from the degradation of PMMA and PC, respectively, and a series of open chain bisphenol-A carbonate oligomers with methacrylate and methyl carbonate terminal groups. The presence of the latter compounds suggests a thermally activated exchange reaction occurring above 300°C between MMA and PC. The presence of bisphenol-A carbonate oligomers bearing methyl ether end groups, generated by a thermally activated decarboxylation of the methyl carbonate end groups of PC, has also been observed among the pyrolysis products. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1873–1884, 1998     

Thermal degradation of poly(olefin sulphone)s. Part I—The effect of olefin structure on the yields of volatile products

The rates and mechanisms of the thermal degradation of nine alternating poly(olefin sulphone)s with different olefin structures have been investigated at 150°C and 200°C by a novel technique which is particularly suitable for studying the initial steps of the degradation. Rapid degradation was initiated at the CS bond with depolymerisation to sulphur dioxide and olefin. The rate of thermal degradation showed a moderate correlation with the ceiling temperature for monomer-polymer equilibrium and also with the number of β-hydrogen atoms, but neither parameter provided an adequate measure of the sensitivity of all the poly(olefin sulphone)s to thermal degradation. Substantial isomerisation was observed in the formation of olefin from poly(3-methyl-1-butene sulphone).     

Thermal degradation of aramids: Part I—Pyrolysis/gas chromatography/mass spectrometry of poly(1,3-phenylene isophthalamide) and poly(1,4-phenylene terephthalamide)

The thermal degradation reactions of poly(1,3-phenylene isophthalamide) or Nomex (I) and poly(1,4-phenylene terephthalamide) or Kevlar (II) aramids have been investigated in the temperature range 300–700°C by pyrolysis/gas chromatography/mass spectrometry. The initial degradation products below 400°C of (I) are carbon dioxide and water. At 400°C benzoic acid and 1,3-phenylenediamine are detected. Benzonitrile, aniline, benzanilide, N-(3-aminophenyl)benzamide as well as carbon monoxide and benzene are evolved in the range 430–450°C. The yields of these products increase rapidly in the range 450–550°C. Isophthalonitrile is observed at 475°C and hydrogen cyanide is detected above 550°C, as are other secondary products such as toluene, tolunitrile, biphenyl, 3-cyanobiphenyl and 3-aminobiphenyl. Pyrolysis of (II) below 500°C evolves only water and trace amounts of carbon dioxide. At 520–540°C the following degradation products have been detected: 1,4-phenylenediamine, benzonitrile, aniline, benzanilide and N-(4-aminophenyl)benzamide. These products as well as carbon dioxide and water increase appreciably between 550°C and 580°C; benzoic acid, terephthalonitrile, benzene and 4-cyanoaniline are also detected in this temperature range. Above 590°C, hydrogen, carbon monoxide, hydrogen cyanide, toluene, tolunitrile, biphenyl, 4-aminobiphenyl and 4-cyanobiphenyl are evolved. Degradation reactions consistent with the formation of these products, which involve initial heterolytic cleavage of the amide linkage for (I) and initial homolytic cleavage of the aromatic NH and amide bonds for (II), are described.     

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 degradation of poly(alkyl acrylates). I. Preliminary investigations

A qualitative survey of the thermal degradation reactions which occur in poly(ethyl acrylate), poly(n-propyl acrylate), poly(isopropyl acrylate), poly(n-butyl acrylate) and poly(2-ethylhexyl acrylate) has been made by using three thermal analytical methods: thermogravimetric analysis (TGA), thermal volatilization analysis (TVA), and the dynamic molecular still (DMS), all combined with infrared and mass spectrometry. Degradation in poly(isopropyl acrylate), which is a secondary ester, becomes discernible at 260°C and proceeds in two stages. The other four polymers, which are all primary esters, are more stable. They degrade in a single-stage process starting at 300°C. The principal volatile products from the primary esters are carbon dioxide and the olefin and alcohol corresponding to the alkyl group. A roughly equivalent quantity of short-chain fragments is also formed. From poly(isopropyl acrylate), carbon dioxide and propylene are the only volatile products in the first phase of the reaction.     

Synthesis and Characterization of Block Copolymers of Poly(Butylenes Terephthalate-Co-Adipate)

The block copolyesters of poly(butylene terephthalate)(PBT) and poly(butylene adipate)(PBA) were prepared by a novel two-stage method. In the first stage, high molecular weight PBT and PBA were melt mixed in the presence of 1,4-butanediol at 275 °C. In the second stage, vacuum was applied to raise the molecular weight. The extent of transesterification was controlled by the proportion of 1,4-butanediol. The sequence distribution and the thermal properties of the block copolyesters were characterized by NMR and DSC respectively.     

HCN evolution from thermal and oxidative degradation of poly(diphenyl methane pyromellitimide) at high temperatures

HCN evolution from thermal and oxidative degradation of poly(diphenyl methane pyromellitimide) has been investigated over a range of temperatures from 500 to 1000°C; rate constants and Arrhenius equations have been determined. Kinetics and mechanisms have been proposed and quantitatively evaluated. They account well for the experimental results. The rate determining steps are C? N scission for thermal degradation and H abstraction from the methylene bridge by O₂ for oxidative degradation, respectively. At high temperatures, oxidation and thermal decomposition of the evolved HCN take place on its passage through the hot zone of the furnace in the highest range of temperatures (800–1000°C). Additional HCN is produced (>800°C) from the char obtained during thermal and oxidative degradation.     

Thermal degradation of poly(alkyl methacrylates)

The thermal degradation of selected poly(alkyl methacrylates) at temperatures between 300 and 800 °C was investigated by pyrolysis gas chromatography. Quantitative characterization of the pyrolysis products yields insights into the mechanism for thermal degradation of poly(alkyl methacrylates) under these conditions. Unsaturated monomeric alkyl methacrylates, carbon dioxide, carbon monoxide, methane, ethane, methanol, ethanol, and propanol were formed during thermal degradation of poly(alkyl methacrylates).     

Thermal degradation of two different polymers bearing amide pendant groups prepared by ATRP method

Piperidinocarbonylmethyl methacrylate (PyCMMA) and 1-(piperidinocarbonyl) ethylmethacrylate (PyCEMA) monomers were synthesized. Polymerizations of PyCMMA and PyCEMA were carried out by atom transfer radical polymerization. The structure of monomers and polymers was characterized by ¹H-NMR, ¹³C-NMR, and FT-IR spectroscopies. Characterization of poly(PyCMMA) and poly(PyCEMA) were carried out using differential scanning calorimetry and gel permeation chromatography. The experimental results showed that the reaction exhibited characteristics of controlled polymerization. The thermal degradation behaviors of poly(PyCEMA) and poly(PyCMMA) were studied using thermogravimetry and a single line vacuum system consisting of a degradation tube with a condenser for product collection. The poly(PyCEMA) and poly(PyCMMA) were heated from ambient temperature to 325 and 500 °C, respectively. The products of degradation were collected as a cold ring fraction (CRF). The CRFs of degradation were investigated by means of IR, ¹HNMR, and GC-MS. For the degradation of both polymers, the major products of CRFs are piperidinocarbonyl methanol and 1,2-dipiperidino,1-oxo ethane. The GC-MS, IR, and NMR data showed that depolymerization below 325 °C to the corresponding monomer was not prominantin the thermal degradation of poly(PyCMMA). The mode of thermal degradation including formation of the major products was identified.     

Poly(Aryl ethers) by nucleophilic aromatic substitution. II. Thermal stability

The thermal stability and degradation process for a specific poly(aryl ether) system have been studied. In particular, the polymer which is available from Union Carbide Corporation as Bakelite polysulfone has been examined in detail. Polysulfone can be prepared from 2,2-bis(4-hydroxyphenyl)propane and 4,4′-dichlorodiphenyl sulfone by nucleophilic aromatic substitution. Because of a low-temperature transition at ? 100°C. and a glass transition at 195°C., polysulfone retains useful mechanical properties from ?100°C. to 175°C. A number of experimental methods were utilized to study the thermal decomposition process for this polymer system. Polysulfone gradually degraded in vacuum above 400°C. as demonstrated by mass spectrometry. Thermogravimetric analysis in argon, air, or high vacuum indicated that rapid decomposition began above 460°C. From gas chromatography, mass spectrometry and repeated laboratory pyrolyses, a number of products from polymer decompositions were identified. The most important degradation process in vacuum or inert atmosphere was loss of sulfur dioxide. Several model compounds representative of portions of poly(aryl ether) molecules were synthesized and the relative thermal stabilities determined. Possible mechanisms for pure thermal decomposition of polysulfone were derived from the product analyses, model studies, and consideration of bond dissociation energies.     

Influence of molecular motions on radiation-induced reactions in polymers

There have been several investigations dealing with the influence of the glass transition on the rate of radiation-induced reactions, especially the crosslinking reaction. On the other hand, no correlation has been reported between secondary transitions and the variation of a reaction rate. In the present work, the degradation of poly(methyl methacrylate) in the temperature range of ?196 to 160°C has been studied. Two breaks in the Arrhenius plot were found. The first one is located at ?5°C and can be correlated with the γ transition, which has been assigned to the hindered rotation of the ester group whose scission initiates the degradation. It is concluded that the thermal excitation of the bond rotation can either increase the scission rate or decrease the recombination rate of reactive intermediates by expanding the cage of the surrounding molecules. If the second mechanism occurs, the rotation of the α-methyl group should also be expected to favor the degradation. However, a second break in the Arrhenius plot was found at ?130°C, and therefore significantly above the δ transition. The influence of this motion is therefore not clear. Certain radiation-induced reactions of poly(vinyl chloride), known from literature, seem to be influenced by a secondary transition. It is concluded that secondary transitions may be significant for scission reactions. This suggests, with respect to the known significance of the glass transition, that the various types of molecular motions in polymers may influence radiation-induced reactions.     

Copoly(arylene ether nitrile) and copoly(arylene ether sulfone) ionomers with pendant sulfobenzoyl groups for proton conducting fuel cell membranes

Three series of fully aromatic ionomers with naphthalene moieties and pendant sulfobenzoyl side chains were prepared via K₂CO₃ mediated nucleophilic aromatic substitution reactions. The first series consisted of poly(arylene ether)s prepared by polycondensations of 2,6‐difluoro‐2′‐sulfobenzophenone (DFSBP) and 2,6‐dihydroxynaphthalene or 2,7‐dihydroxynaphthalene (2,7‐DHN). In the second series, copoly(arylene ether nitrile)s with different ion‐exchange capacities (IECs) were prepared by polycondensations of DFSBP, 2,6‐difluorobenzonitrile (DFBN), and 2,7‐DHN. In the third series, bis(4‐fluorophenyl)sulfone was used instead of DFBN to prepare copoly(arylene ether sulfone)s. Thus, all the ionomers had sulfonic acid units placed in stable positions close to the electron withdrawing ketone link of the side chains. Mechanically strong proton‐exchange membranes with IECs between 1.1 and 2.3 meq g⁻¹ were cast from dimethylsulfoxide solutions. High thermal stability was indicted by high degradation temperatures between 266 and 287 °C (1 °C min⁻¹ under air) and high glass transition temperatures between 245 and 306 °C, depending on the IEC. The copolymer membranes reached proton conductivities of 0.3 S cm⁻¹ under fully humidified conditions. At IECs above ∼1.6 meq g⁻¹, the copolymer membranes reached higher proton conductivities than Nafion^® in the range between −20 and 120 °C. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of some aliphatic poly(ester-β-sulfone)s by a novel method

A new synthetic method of preparing poly(ester-β-sulfone)s from sodium formaldehyde sulfoxylate (SFS) and a diacrylate monomer (1,6-hexanediol diacrylate or 1,9-nonanediol diacrylate) in aqueous solution was studied. The structures of poly(ester-β-sulfone)s were identified and their crystal morphology analyzed. It turned out that the poly(ester-β-sulfone)s crystals were ring-shaped spherulites. The melting point of both poly(ester-β-sulfone)s was 97°C and 116°C, respectively. The thermal degradation temperature in both cases was close to 281°C.     

Crystal structure of poly(dithiotriethylene adipate)

The crystal structure of poly(dithiotriethylene adipate) has been determined through the best fitting of calculated and experimental X‐ray diffraction powder profiles. A triclinic cell was found with dimensions a = 4.942 (7) Å, b = 4.702 (2) Å, c = 20.56 (2) Å, α = 88.9 (2)°, β = 61.0 (1)°, γ = 67.8 (1)°, P‐1 space group, and one chain in the unit cell. A full extended trans conformation of the chain fitted satisfactory the experimental data, yielding to a discrepancy factor R_p = 0.073. A comparison between the crystal structures of poly(dithiotriethylene adipate) and poly (thiodiethylene adipate) is proposed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2677–2682, 2005     

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     

Thermal degradation of polymers with phenylene units in the chain. II. Sulfur-containing polyarylenes

Poly(p-phenylene sulfide), a poly(arylene sulfone), and a poly(arylene sulfonate) were subjected to thermal degradation in vacuo, at temperatures between 250 and 620°C. The volatile and solid degradation products were analyzed by mass spectroscopy, infrared spectroscopy, and elemental analysis. The major decomposition product of poly-(phenylene sulfide) is a condensate, which consists of di- and trimeric chain fragments, dibenzothiophene, and possibly thianthrene. The residual polymer loses two thirds of its sulfur as hydrogen sulfide, however, one third is retained even at 620°C. The most characteristic decomposition reaction of the polysulfone and of the polysulfonate is the almost complete removal of the sulfur as sulfur dioxide. The elimination of sulfur dioxide is practically complete at 450°C for the polysulfone and at 350°C for the polysulfonate.