The thermal degradation of copolymers of vinyl acetate with methyl methacrylate and other monomers

The thermal degradation of copolymers of vinyl acetate with methyl methacrylate, styrene and ethylene has been investigated using thermal volatilization analysis and thermogravimetry, together with analysis of volatile and involatile degradation products. All three copolymer systems show some of the features characteristic of the homopolymers of the monomers concerned. There is evidence, however, for an intramolecular lactonization process in VA—MMA copolymers, involving reaction of adjacent VA and MMA units with elimination of methyl acetate. This reaction occurs less readily than the analogous process in vinyl chloride—MMA copolymers. Mechanisms of the various degradation reactions are discussed.     

Thermal degradation of copolymers of 2-hydroxyethyl methacrylate and alkyl methacrylates

Thermal degradation of homopolymers of ethyl methacrylate (I), n-butyl methacrylate (II), 2-hydroxyethyl methacrylate (III), and copolymers of III with I and II were carried out by thermal volatilization analysis (TVA) up to 440°C with subsequent subambient thermal volatilization analysis (SATVA). An on-line mass spectrometry coupled with TVA and SATVA was employed to identify the products of thermal degradations. Isothermal pyrolyses of the polymers were carried out separately at 400°C in vacuum for 30 min and the liquid products of decomposition were collected and analysed by gas chromatography. The relationship between the amounts of I and II obtained from pyrolysis and the amounts of these components actually present in the copolymer samples was determined. Also the amount of III and ethyleneglycol dimethacrylate obtained from pyrolysis increases with the amount of III in the copolymer. The polymers were also characterized by differential thermal analysis.     

Preparation and degradation of copolymers of methyl methacrylate with alkali metal methacrylates—II: Thermal analysis of the copolymers,nature of the degradation products and general characteristics of the degradation reaction

Three series of copolymers, each spanning the composition range from alkali metal methacrylate homopolymer to methyl methacrylate homopolymer, have been prepared; their degradations have been studied under programmed heating conditions, by means of simultaneous thermogravimetry and thermal volatilization analysis (TVA) in a vacuum system and by differential thermal analysis in dynamic nitrogen. Total volatile products have been characterised by infrared spectroscopy, subambient TVA and GLC. The thermal analysis data suggest that the two types of monomer unit tend to participate in degradation processes in different temperature ranges. However, in addition to those products characteristic of the degradation of each homopolymer, the copolymers give substantial amounts of methanol; this product must arise from a reaction specific to the copolymer structure.     

Thermal degradation of poly(vinyl bromide), vinyl bromide-methyl methacrylate copolymers,and poly(vinyl bromide)-poly(methyl methacrylate) blends

Degradation behavior has been compared for PVB, five VB-MMA copolymers which span the composition range, PMMA, and PVC by using thermogravimetry in dynamic nitrogen and thermal volatilization analysis (TVA) under vacuum for programmed heating at 10°C/min. Volatile products have been separated by subambient TVA and identified. PVB is substantially less stable than PVC but shows inmost respects analogous degradation behavior. The introduction of VB into the PMMA chain leads to intramolecular lactonization with release of methyl bromide at temperatures a little above 100°C; after this reaction is complete, however, the polymer is more stable toward volatilization than PMMA. Copolymers with moderate and high VB contents also lose hydrogen bromide. Carbon dioxide is a significant product at intermediate compositions. The variation of product distribution with copolymer composition is discussed in relation to the several reactions involved and comparisons are made with VC-MMA copolymers. PVB-PMMA blends snow some features of degradation behavior in common with the PVC-PMMA system but also very important differences. The effect of PVB is only to stabilize the PMMA; the mechanism is discussed. The role of PVB as an additive and VB as a comonomer for fire-retardant PMMA compositions is briefly considered in relation to earlier studies.     

Thermal degradation of graft copolymers of PVC prepared by mastication with styrene and methyl methacrylate,and of further PVC mixtures and vinyl chloride copolymers

Graft copolymers prepared by mastication of PVC in the presence of styrene or of a styrene/ methyl methacrylate mixture, have been studied by thermogravimetry, estimation of hydrogen chloride, thermal volatilization analysis, and flash pyrolysis/g.l.c. The degradation behaviour of PVC/ polystyrene mixtures, vinyl chloride/styrene random copolymers, a random copolymer of methyl methacrylate and styrene, and PVC/poly-α-methylstyrene mixtures has also been studied. The graft copolymers resemble the PVC/methacrylate graft copolymers previously studied in showing retardation of the dehydrochlorination reaction, but contrast with them in yielding chain fragments but no monomer during HCl production. Some stabilization of the second component at higher temperatures is also found. PVC/polystyrene mixtures behave in the same way as the corresponding graft copolymers, but vinyl chloride/styrene copolymers show reduced stability towards both dehydrochlorination and monomer production compared with the homopolymers. PVC/poly-α-methylstyrene mixtures yield some monomer concurrently with HCl loss, and display marked retardation of the latter reaction. Stabilization of the second polymer at higher temperatures is again observed. Many of these results add further strong support to the view that chlorine atoms are involved as chain carriers in the thermal dehydrochlorination of PVC.     

The thermal degradation of copolymers of methyl methacrylate with methacrylic acid

The degradation has been studied using thermogravimetry and thermal volatilization analysis; product analysis has been carried out by GLC and spectroscopy. The copolymers yield water and methanol below 300°; at higher temperatures, the products also include methyl methacrylate, carbon monoxide, carbon dioxide and methane. Quantitative comparison of the yields of methanol and methyl methacrylate has been made with predicted yields based upon sequence distribution calculations. Methanol is believed to result by two routes (i) intramolecular cyclization of adjacent ester and acid chain units at low temperatures, and (ii) fragmentation of ester units, in competition with depolymerization, at higher temperatures. Methyl methacrylate yields are substantially lower than the MMA content of the copolymer, as a result of these processes; some MMA units also appear in the product fraction volatile at degradation temperatures but not at ambient temperature. The partially-degraded copolymers develop anhydride ring structures in the chain as a result both of dehydration and of methanol production. The mechanisms of the various reactions are discussed.     

Speciation of Volatile Selenium Species in Plants Using Gas Chromatography/Inductively Coupled Plasma Mass Spectrometry

 Gas chromatography/inductively coupled plasma mass spectrometry (GC/ICP MS) coupled with solid phase micro extraction can provide a simple, extremely selective and sensitive technique for the analysis of volatile sulfur and selenium compounds in the hea     

气相色谱/电感耦合等离子体质谱测定植物中挥发性硒化合物

Severalinstrumentalmethodscanbeusedforthedetectionanddeterminationofvolatileselenium(Se)andsulfur (S)compounds .Theserelyprimari lyongaschromatography (GC)forseparationanddifferentdetectiontechniques ,includingatomice missiondetection (AED ) ,massspectrom…     

Thermal degradation of copolymers of styrene and acrylonitrile. I. Preliminary investigation of changes in molecular weight and the formation of volatile products

By the use of thermal volatilization analysis (TVA), 292°C was chosen as a suitable temperature for a preliminary experimental survey of the thermal degradation of styrene–acrylonitrile copolymers. TVA also indicated that there is no fundamental change in reaction mechanism as the acrylonitrile content of the polymer is increased from zero to 33.4% although there is a progressive increase in the rate of volatilization. The increase in the rate of volatilization over that of polystyrene is directly proportional to the acrylonitrile content of the copolymer. From the changes in molecular weight which occur during the reaction it is clear that the primary effect of the acrylonitrile units on stability is to cause an increased rate of chain scission, but there is a small proportion of “weak links” which are associated with the styrene units and which are broken instantaneously at 292°C. The number of monomer molecules liberated per chain scission, the zip length, is about 40 for polystyrene in the initial stages of degradation and decreases only to the order of 20 even in copolymer containing 24.9% acrylonitrile. Thus the unzipping process is not severely affected by the acrylonitrile units; this is borne out by the fact that acrylonitrile appears among the products in very much greater concentrations than from pure polyacrylonitrile. The proportion of larger chain fragments (dimer, trimer, etc.) also increases with acrylonitrile content.     

Thermal degradation of copolymers of 36Cl-vinyl chloride and methyl methacrylate

The degradation of copolymers of vinyl ³⁶Cl-chloride and methyl methacrylate has been studied using film samples, slow heating rate and high vacuum conditions. Volatilization has been followed using thermal volatilization analysis and radioactive assay of methyl chloride and hydrogen chloride. By carrying out duplicate experiments with and without an ice trap at ? 100°, it is possible to measure methyl chloride alone and both products, respectively, so that each product can be estimated. Yields have been found to agree well with those predicted from sequence distribution calculations. Some differences in behaviour compared with earlier work using powder samples and nitrogen flow conditions are discussed.     

Unusual, promoted release of guests from amphiphilic cross-linked polymer networks

Hyperbranched fluoropolymer-poly(ethylene glycol) (HBFP-PEG) cross-linked networks have been found to exhibit capabilities for the encapsulation of high levels of geraniol guest molecules coupled with unusually rapid release of the volatile compound. The promotion of the release of the volatile fragrance geraniol, observed as decreasing volatilization temperatures and increasing volatilization rates by thermogravimetric analyses, was found to be dependent upon the HBFP-PEG network composition, with increasing effects from decreasing wt % PEG and a maximum effect occurring at 5 wt % PEG.     

Analysis of polystyrene-b-polyisoprene copolymers by coupling of liquid chromatography at critical conditions to NMR at critical conditions of polystyrene and polyisoprene

For the investigation of the molecular heterogeneity of polystyrene-b-polyisoprene block copolymers, a chromatographic separation method, namely liquid chromatography at critical conditions was developed. This method was coupled on-line with (1)H-NMR(where NMR stands for nuclear magnetic resonance) for the comprehensive analysis of the polystyrene-b-polyisoprene copolymers. The copolymers were synthesized by two different methods: sequential living anionic polymerization and coupling of living precursor blocks. While (1)H-NMR allows just for the analysis of the bulk chemical composition of the block copolymers, the coupling with liquid chromatography at critical conditions provides selective molar mass information on the polystyrene and polyisoprene blocks within the copolymers. The polyisoprene block molar mass is determined by operating at chromatographic conditions corresponding to the critical point of adsorption of polystyrene and size exclusion chromatography mode for polyisoprene. The molar mass of the polystyrene block is determined by operating at the critical conditions of polyisoprene. In addition to the molar mass of each block of the copolymers, the chemical composition distribution of the block copolymers was determined. By using the coupling of liquid chromatography at critical conditions to (1)H-NMR, one can also detect the homopolymers formed during synthesis. Finally the microstructure of the polyisoprene block in the copolymers was evaluated as a function of molar mass.     

Thermal degradation of copolymers of methyl methacrylate and methyl acrylate. I. Products and general characteristics of the reaction

The technique of thermal volatilization analysis (TVA), applied to methyl methacrylate–methyl acrylate copolymers having molar composition ratios 112/1, 26/1, 7.7/1, and 2/1, has demonstrated that the stabilization of poly(methyl methacrylate) by copolymerized methyl acrylate is due to inhibition of the depolymerization initiated at terminally unsaturated structures, probably by direct blockage by methyl acrylate units. The molecular weight of the copolymers decreases rapidly during degradation, suggesting that a random scission process is involved. The products of degradation consist of the monomers, carbon dioxide, chain fragments larger than monomer, and a permanent gas fraction which is principally hydrogen. Infrared and ultraviolet spectral measurements suggest that the residual polymer, which is colored, incorporates carbon–carbon unsaturation. The complete absence of methanol among the products is surprising in view of its abundance among the products of degradation of poly(methyl acrylate). These observations have been accounted for qualitatively in terms of acceptable polymer behavior.     

Synthesis of methacrylic copolymers with nona‐1‐butoxy trititanosiloxane as side groups and its application as a thermosetting resin

Methacrylic copolymers with a hydroxyl group on one end of the main chain and nona‐1‐butoxytrititanosiloxane as side groups (called methacrylic hybrid copolymers) were synthesized for use as baked‐finish‐type coating resins. The chemical structures of the side groups in the methacrylic hybrid copolymers were confirmed with the ash weight of the copolymers after combustion, the elemental ratio analysis of Si and Ti in the ash determined by inductively coupled plasma emission spectrometry, and the characteristic absorption band determined by Fourier transform infrared spectrophotometry. The methacrylic hybrid copolymers were cured at temperatures less than 150 °C in the absence of a curing accelerator. The cured copolymers exhibited a high thermal stability. The curing temperature of the copolymers was determined by the change in the absorption peak strength (peak area) of the 1655 cm⁻¹ band in the IR difference spectrum. The thermal stability of the copolymers was evaluated as the thermal‐degradation temperature measured by thermogravimetric analysis. The methacrylic hybrid copolymers were then be used as effective curing resins. The mixture, consisting of thermoplastic methacrylic terpolymer with hydroxyl and carboxyl groups and the methacrylic hybrid copolymers, were cured at less than 150 °C in the absence of a curing accelerator and exhibited a higher thermal‐degradation temperature than the copolymers. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1090–1098, 2001     

Thermal degradation behavior of blends of phenyl methacrylate-styrene copolymers with aluminum isopropoxide

Thermal degradation studies were carried out of copolymer phenyl methacrylate-styrene in the presence of aluminum isopropoxide to assess the stability and alteration of degradation mechanism using thermogravimetry-differential thermogravimetry (TG-DTG) in inert atmosphere and under vacuum using thermal volatilization analysis (TVA). After collecting the condensable volatile degradation products from TVA experiments and separating them by sub-ambient TVA, investigation and identification were effected out by IR spectroscopy and gas chromatography-mass spectrometry (GC-MS) techniques. The degradation products from the blends consisted of some additional products, i.e., isopropanol, phenol, methacrylic acid, ethyl benzene, benzene and a cyclic compound apart from similar products obtained from the degradation of pure copolymers. The mechanism of newly formed degradation products has been discussed in detail. This revised version was published online in August 2006 with corrections to the Cover Date.     

New Chromatographic and Hyphenated Techniques for Hydrophilic Copolymers

Most synthetic polymers are distributed in more than one parameter of molecular heterogeneity. For hydrophobic copolymers there are different chromatographic techniques available to analyse these distributions. As a result of the increasing interest in hydrophilic polymers and copolymers new chromatographic techniques are developed for the characterization of these polymers as well. However, very frequently these polymers contain highly polar or charged functional groups making them soluble only in aqueous mobile phases. There are several problems related to the use of aqueous mobile phases in polymer chromatography. Even the SEC analysis of such copolymers is not straightforward. As for HPLC in aqueous mobile phases, there are only a few applications in the literature so far. In addition to the fact that only a very limited number of stationary phases is available for aqueous HPLC of polymers, the interactions of polyelectrolytes in such chromatographic systems are not well understood. The present paper addresses the problems related to the application of SEC and HPLC in aqueous mobile phases. For graft copolymers with a polyethylene oxide backbone, e.g. PEG-g-polymethacrylic acid and PEG-g-polyvinyl alcohol, it will be shown that methods can be developed that give accurate molar mass and chemical composition information. Two-dimensional chromatography where aqueous HPLC and SEC are coupled on-line will be shown to be the most powerful analysis tool for the analysis of such copolymers. The hyphenation of the chromatographic separation techniques with spectroscopic detection techniques provides further insight into the molecular complexity of these copolymers.     

Degradation thermique des copolymeres methacrylate de methyle-chlorure de vinylidene

The thermal degradation, under inert atmosphere, of a set of methyl-methacrylate-vinylidene chloride copolymers prepared by free radical copolymerization with constant composition conditions, is studied by thermogravimetry coupled with titration of HCl evolved and with gas chromatographic analysis of volatile products (monomers, methyl chloride). Only the formation of methyl methacrylate can be related to the sequence distribution.     

Thermal volatilization analysis: A new method for the characterization of polymers and the study of polymer degradation

In a continuously evacuated system in which volatile products are passing from a heated sample to the cold surface of a trap some distance away, a small pressure will develop which varies with the rate of volatilization of the sample. If this pressure (measured by Pirani gage) is recorded as the sample temperature is increased in a linear manner, a TVA thermogram showing one or more peaks is obtained. TVA thermograms for a number of polymers and copolymers are presented and briefly discussed. The technique has some advantages over TGA for characterizing polymers or studying qualitative aspects of polymer degradation.     

Evaluation of methods for the separation of trimethylselenonium ion as a major,minor or general metabolite using neutron activation analysis

Trinethylselenonium (TMSe) ion was separated by dual-column ion-exchange chromatography and assayed by neutron activation analysis. The TMSe content of the selenium in human urine was found to be (14±2)%, consistent with literature values. An altemate, published, multi-step procedure employing Reineckate precipitation followed by decomposition/volatilization conversion of selenium into dimethylselenide, perchloric acid digestion into selenite and subsequent analysis employing inductively coupled plasma mass spectrometry (ICP-MS) was evaluated. A maximum recovery of TMSe was estimated at 32%. It has been suggested that losses in each step of a multi-step procedure yield low recoveries as reported in the literature.     

Zur Ermittlung der Äthylen-Sequenzlängenverteilung und der chemischen Uneinheitlichkeit in Copolymeren mit Propylen durch Pyrolyse-Gas-Chromatographie

Pyrolysis coupled with gas chromatography has been applied to investigate the sequence distribution in copolymers of ethylene and propylene. The copolymers analyzed have been prepared with soluble Ziegler-Natta-catalysts and show different degrees of crystallinity. In one series of samples the methyl group of the propylene units has been labeled with tritium. It was then possible to detect carbons by flame ionization detector and simultaneously the methyl groups by the radio-detector in parallel. Within the errors of these methods the results from both detectors are consistent with the calculations from kinetics. The accuracy of the data is best in copolymers with long ethylene sequences. By GPC fractionation a heterogeneity in the chemical composition can be observed. One component of the copolymers is of high molecular weight, while the other has a molecular weight of less than 1000 and is very rich in ethylene. The influence of chemical heterogeneity on sequence distribution derived from kinetics and pyrolysis has been discussed. A mechanism in which chains with different chemical composition are growing from different species of the catalyst has been proposed. The experimental results show that the heterogeneity is not critical for the sequence analysis by kinetics and pyrolysis.