Thermal Degradation Of Polymers Research Articles

Thermal stability and degradation of hydrocarbon metathesis polymers

The thermal stability of poly(dicyclopentadiene), made with RuCl 2( p-cymene)(PCy 3) as initiator, was investigated by ageing 2 and 5 mm plates up to 1 year at 180°C in air, or 360 h in a weather-o-meter. The surface roughness and microhardness of unstabilized and stabilized (0.1% Irganox® 1520, 0.5% Tinuvin® 171) probes were determined. Stabilization leads to an overall softer material but with a harder surface oxide layer with finer cracks, limiting the oxygen diffusion rate into the material and therefore protecting the underlaying material from fast oxidation. This is further supported by chemiluminescence (CL) measurements of 50 and 150 μm films of poly(DCPD) under strong oxidative conditions (150°C in pure O 2). It was found that even the unstabilized material is extremely resistant to oxidation, far superior to saturated poly( α-olefins) like poly(propylene). Pyrolysis of poly(DCPD) and poly(cyclooctene) (Vestenamer®) at 670°C under an inert atmosphere gave mixtures of cyclic and open-chain unsaturated hydrocarbons. Surprisingly, the pyrolysis of poly(norbornene) (Norsorex®) gives squalene in >90% yield.

A theory for quasi-steady single-step thermal degradation of polymers

A theory for approximately steady thermal degradation of solids is developed from a superset of nonlinear integral-differential equations. The theory extends previous work, using a degradation model that is more consistent than previously published models and fully accounts for surface radiation losses. The thermal decomposition of the solid is assumed to follow a single-step first-order Arrhenius reaction. A quasi-steady regime is identified and approximate solutions are compared with experimental results for PMMA and numerical results obtained by integrating the full model. The numerical solutions are found to compare well with experimental results and the approximate solutions compare well with the numerics. Furthermore, it is found that the quasi-steady mass loss rate gives a good estimate of the average mass loss rate even during thermally thin degradation. To simplify interpretation and to aid the analysis, the degradation kinetics are re-cast in terms of a critical temperature and a critical temperature range. Application of the theory to practical situations and other modelling approaches is also discussed.

Applications of molecular dynamics to the study of thermal degradation in aromatic polymers. I: Polystyrene

AbstractThis paper reports recent progress in the development of a generic molecular dynamics model that accounts for the major chemical reactions involved in the thermal degradation of polymers. The strategy employed in the design of the most recent version of this model was to interface our code for performing reactive dynamics on simple vinyl polymers with a commercial molecular dynamics package (Discover 95). The expanded range of applicability of the integrated model is illustrated by applying it to the study of thermal degradation in atactic polystyrene.

Solubility, curing and heat resistance of some ester-imide oligomers as a function of the nature and content of some comonomers

Abstract Substitution of ethyl glycol by neopentylglycol in ester-imide oligomers increases solubility and decreases glass transition temperature, while increase of quantity of dimethylterephthalate has opposite effects. Oligomer containing neopentylglycol and the lower quantity of dimethylterephthalate, which dissolves even in mixtures of methyldipropyleneglycol/xylene or toluene 1 1 by weight to obtain 40% or more concentrated solution, is the most convenient. Heat resistance, mechanical and electrical properties, and dielectric losses are optimum if oligomers are cured by heating for 4 h at 260°C. Curing consists in increase of molecular weight and transformation of oligomers in polymers by the elimination of water and diols. Thermal degradation of polymers involves three stages: elimination of unreacted comonomers and of a part of bound diols; elimination of the rest of diols, dimethylterephthalate and tris-(2-hydroxyethyl)isocianurate; elimination of structures trimellitic anhydride — diaminodiphenylmethane containing aromatic and imidic rings. Neopentylglycol and large quantities of dimethylterephthalate reduce the heat resistance of polyester-imides.

Conductive Polymer Composites

The modification of electrical and mechanical properties of a low-density polyethylene (LDPE) filled with copper particles, having an average diameter of 40 μm, has been analyzed. A drastic decrease of the electrical resistivity of the composites is observed, about 14 orders of magnitude when 40 volume percent of copper is added. The mechanical properties of the composites are poor. Accelerated thermal tests were carried out and they did not reveal significant polymer thermal degradation in the presence of the copper particles. Melt mixing is by far superior to dry blending for sample preparation due to a much better homogenization of particles within the polymer matrix. An on-going work focuses on improvement of the mechanical properties by using coupling agents.

Studies on the Thermal Degradation of Acrylic Polymers by Simultaneous Autostep TG/DTA

Simultaneous autostep technique, a novel methodology in thermal analysis, was employed for the investigation of multiple stage degradation of acrylic polymers in thermogravimetric (TG) and differential thermal analysis (DTA) methods. Heating of the sample was controlled automatically with respect to the rate of mass loss in each degradation step in addition to the control of heating by a given steady heating rate. Three standard samples (polymethyl acrylate, polymethyl methacrylate, and polystyrene) and a newly synthesized polymer (polycinnamoyloxyethyl methacrylate) were taken to study the advantages of this technique for the better understanding of thermal degradation of polymers involving a multiple stage decomposition pattern over the conventional method. Results from this method revealed information about the degradation of acrylic polymers in a more precise and accurate manner and were compared with those of the conventional method.

The effect of chain-end groups on the thermal stability of poly(ethyl methacrylate)

The thermal degradation behavior of poly(ethyl methacrylate) homopolymers, synthesized by using a sulfur dioxide—tert-butyl hydroperoxide (SO 2-TBHP) redox pair at different temperatures (12–35 °C) was investigated. The thermal behavior of samples was followed by dynamic thermogravimetry in a nitrogen atmosphere. Contrary to some reports in the literature, the thermal degradation of polymers has been observed to take place in multi-steps. These are assigned to the loss of labile end groups, side chain scission, anhydride formation and main chain degradation steps. The thermal stability of the polymer samples synthesized by using a SO 2-TBHP redox pair has been compared with the thermal stability of the polymers synthesized by using azobis-isobutyronitrile (AIBN), tert-butyl hydroperoxide (TBHP), and benzoyl peroxide (BPO). The polymers synthesized by using the SO 2-TBHP redox pair showed greater stability against thermal degration.

Thermal degradation of high performance polymers—influence of structure on polyimide thermostability

This work deals with the thermostability and thermal behavior of polyimide materials such as bismaleimide and bisnadimide, which are usually used in aeronautic and electronic applications in high temperature environments. The thermostability of these materials has been studied by thermogravimetry analysis (TGA) both in air and in nitrogen to determine thermal and thermo-oxidative phenomenon. Limiting Oxygen Index (LOI) values have been determined and compared with the LOI of a PolyEther Imide thermo-plastic polymer. Products which are formed during thermal degradation have been identified using mass spectrometry and relationships between LOI. During thermal degradation, water, carbon monoxide and carbon dioxide are the most important products formed; the major organic compounds detected were aniline, polycyclic molecules and isocyanate products. LOI increases with the number of crosslinking points, either maleimide or nadimine types. Results also show a high sensitivity to oxygen for these materials and they indicate that the nadimide function increases material thermostability.

Kinetic compensation effect in the thermal degradation of polymers

The kinetic study of thermal degradation takes into account the validity of the Arrhenius equation. From TG data, the activation energy,E a and pre-exponential factor,A, are evaluated. These results are interpreted by using the ‘kinetic compensation effect’ as basis. A linear correlation between In(A) andE a is obtained in all cases studied. However, in a plot of the logarithm of the rate constant as a function of reciprocal temperature for the same series of reactions, the thermal oxidative degradations of Nylon-6 and PVC display a point of concurrence and one isokinetic temperature, whereas those of HIPS and PC do not. Therefore, in the thermal oxidative degradations of Nylon-6 and PVC a ‘true’ compensation effect occurs, which could be related to the bulk properties of metal oxides, such as different valence states, whereas for other polymers it displays only an ‘apparent’ compensation effect. This means that degradation is largely independent of the bulk properties of oxides, but may be related to the distribution of different kinds of active links in the polymer surface having different activation energies.

Effects of alkali halides on the thermal decompositions of poly(methyl methacrylate) and poly(2‐hydroxy ethyl methacrylate)

The effects of alkali halides on the nonoxidative thermal degradations of poly(methyl methacrylate) and poly(2-hydroxy ethyl methacrylate) are described. The magnitudes of the effects of various alkali halides on polymer thermal degradation were found to depend on the salt and the polymer. Mass spectrometric analysis of volatiles evolved during polymer degradation detected alkyl halides formed by reactions between the salts and polymers. Compared to poly(methyl methacrylate), more alkyl halide was evolved from samples containing alkali halides and poly(2-hydroxy ethyl methacrylate). To varying degrees, salts also catalyzed ester decomposition reactions for this polymer. Infrared spectroscopic analysis results showed that carboxylate salts, carbonate, and carbon monoxide were formed by heating polymer/salt mixtures. © 1996 John Wiley & Sons, Inc.

Diagnosing mechanisms of oligomer formation in the thermal degradation of polymers

When attempting to find the mechanisms involved in the thermal degradation of polymers, a problem arises when oligomers are observed as the principal products of thermal decomposition. In this case, one or more of at least three different general mechanisms may be responsible: 1. (i) a high degree of random scission, 2. (ii) intramolecular transfer during unzip, and/or 3. (iii) secondary reactions of the primary products. This paper illustrates how these mechanisms can be differentiated by: 3.1. (i) appropriate statistical plots of the yields of the products, 3.2. (ii) quantitative measurements of rate constants for the evolution of the volatiles, and 3.3. (iii) measurements of product yields and ratios as a function of sample size. Examples of the deduction of oligomer formation mechanisms are chosen from results for the following polymers: BIOPOL, polyisobutylene, polymethylacrylate, natural rubber, and polystyrene.

Thermal degradation of polymers in the melt, 2. Kinetic approach to the formation of volatile oligomers by thermal degradation of polyisobutylene

AbstractThe thermal degradation of polyisobutylene is characterized by kinetics consisting of four types of intramolecular hydrogen abstraction (back‐biting) of primary (p) and tertiary (t) terminal macroradicals (R and R) and the successive β scission at the inner position of the main chain. This reaction affords four types of terminal monoolefins in the volatile oligomers. Assuming the reaction occurs competitively under a steady state regarding the on‐chain macroradicals, the composition of the monoolefins are represented as the rate ratios of the respective back‐biting processes. The rate ratio between the abstractions of different types of hydrogens (CH2 and CH3) from the same type of macroradicals is expressed only by the rate constant ratio. The (TTD)p/(TVD)p and (TTD)t/(TVD)t ratios remain constant during degradation, independently of the decreases in volume and molecular weight of the reacting polymers and this tendency agrees fairly well with the kinetic expectation. This result suggests that back‐biting depends only on the local motion of the reacting chain ends. The ratios between the abstractions of the same type of hydrogen from different macroradicals are expressed by the product of the rate constant ratio and the integrated macroradical concentration ratio ([R]/[R]). The observed values of (TTD)p/(TTD)t and (TVD)p/(TVD)t decrease with reaction time. This decrease results from the decrease in macroradical concentration.

Thermal degradation of polymers in the melt, 1. Characterization of volatile oligomers formed by thermal degradation of polyisobutylene

AbstractChemical structures of a number of components of volatile oligomers including (n+2)‐mers (n ≧ 0) produced by thermal degradation of polyisobutylene were systematically determined by high‐resolution capillary gas chromatogaphy/mass spectrometry (GC/MS). The total ion current (TIC) chromatogram consists of about 100 peaks ranging from dimers (2‐mers, n = 0) to dodecamers (12‐mers, n = 10) and most of the main peaks are classified into four types of terminal monoolefins: a trisubstituted olefin with a tert‐butyl end, a vinylidene olefin with a tert‐butyl end, a trisubstituted olefin with an isopropyl end, and a vinylidene olefin with an isopropyl end. The formation of these monoolefins is reasonably interpreted by intramolecular hydrogen abstractions (back‐biting) of primary and tertiary terminal macroradicals and subsequent β; scissions at the inner position of the main chain. In all the chromatograms of each (n+2)‐mer (n ≧ 1), the retention times of terminal trisubstituted types of monoolefins were shorter than those of terminal vinylidene types of monoolefins, in contrast to the elution order of dimers. The relative intensities between the interesting peaks of each (n+2)‐mer (n ≧ 1) clearly represent that back‐biting more predominantly occurs at the methylene hydrogen rather than at the methyl group consistent with the difference in the bond dissociation energy of the HC bond of interest, as opposed to the steric hindrance mechanism5,7.

Polymer degradation discussion group— Thermal degradation of polymers—in honour of professor Norman Grassie

Polymer degradation discussion group— Thermal degradation of polymers—in honour of professor Norman Grassie

Polymer degradation discussion group, thermal degradation of polymers, in Honour of prof. Norman Grassie

Macromolecular Rapid CommunicationsVolume 16, Issue 3 p. 231-231 Announcement Polymer degradation discussion group, thermal degradation of polymers, in Honour of prof. Norman Grassie First published: March 1995 https://doi.org/10.1002/marc.1995.030160314AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume16, Issue3March 1995Pages 231-231 RelatedInformation

Polymer degradation discussion group, thermal degradation of polymers in honour of prof. Norman Grassie

Polymer degradation discussion group, thermal degradation of polymers in honour of prof. Norman Grassie

Polymer degradation discussion group, thermal degradation of polymers in Honour of Prof. Norman Grassie

Polymer degradation discussion group, thermal degradation of polymers in Honour of Prof. Norman Grassie

An enclosed Curie point pyrolysis-GC technique for studying the oxidative or thermal degradation of polymers and volatile oligomeric oils

The technique of pyrolysis-GC has been extended to the study of oxidative degradation by a method that can also deal with volatile oil samples and oligomers. This has been done by pre-degrading the sample in a sealed capillary tube containing either air or inert gas, and then breaking open this tube within the carrier gas flow at the injection port of a GC apparatus. This approach is possible because the sample is deposited on a Curie-point filament wire within the sealed tube, and this wire can be rapidly heated in the usual way by an external RF field. The new technique can therefore be described as enclosed Curie-point pyrolysis (ECP). Although there is a need for improving the reproducibility of the absolute product yields obtained by ECP, the relative yields of products display very good reproducibility. Examples of the use of the approach to study the oxidation of polyisobutylene oils are provided. The results show distinct oxidation products which are not present in the thermolysis pyrograms. A comparison of results from conventional resistive filament pyrolysis with those from the ECP method provides a procedure for distinguishing gas-phase versus melt-phase secondary reactions of the pyrolysis and oxidation products.

Initiation processes in polymer degradation

Thermal degradation of vinyl polymers often occurs by a free radical propagation process and thermooxidative degradation almost always does. The nature of the initiation process, particularly in commercial polymers, is not well understood and is normally considered to be be due either to homolysis of the weakest CC or CH bond in the molecule or to the direct reaction of oxygen with the polymer to give free radicals. In practice neither of these is likely under conditions to which polymers are subjected during manufacture and use and the evidence suggests that mechanochemical scission of the polymer chain to macroalkyl radicals is the primary initiating process leading to the formation of hydroperoxides which are the cause of subsequent degradation. It is shown that alkyl radical traps effectively remove macroalkyl radicals during processing, thus delaying mechanooxidation. The nitroxyl radicals formed also contribute to subsequent environmental stabilisation of elastomers and thermoplastic polymers.

Thermal degradation of polymers of captodative substituted olefins

AbstractThermal degradations of the polymers of some captodative substituted olefins were studied by means of thermal gravimetry, infrared and electron paramagnetic resonance (EPR) spectroscopy, and evolved gas analysis. It was found that the initial degradation temperature of the homopolymers varies from 166 to 291°C and is correlated to the magnitude of the EPR coupling constant of the β‐hydrogen of the radicals derived from the corresponding captodative olefins. It was also found that poly(methyl α‐methoxyacrylate) depolymerizes to the monomer, while poly(α‐cycanovinyl acetate) eliminates mainly acetic acid to give a polyene.