Palanichamy Sivasamy

The role of β-hydrogen in the degradation of polyesters

Abstract Linear polyesters based on phthalic anhydride and any one of the following C 4 diols, 1,4-butanediol, 2-butene-1,4-diol or 2-butyne-1,4-diol were synthesised by the melt condensation technique and characterised by infrared spectroscopy. The thermal degradation of the polyesters was carried out under high vacuum and the products separated and identified using gas chromatography—mass spectrometry. The results revealed that a decrease in the β-hydrogen content of the diol component leads to a decrease in the amount of phthalic anhydride formed during degradation. It was also observed that the amount of diol released during the degradation of the polyesters increases with the decrease in the β-hydrogen content of the diol component. The results emphasise the fact that β-scission is one of the primary degradation processes in polyesters when β-hydrogen atoms are available in the diol component.

A kinetic analysis of thermogravimetric data of radically polymerised N-phenylmaleimide

Abstract The thermal behaviour of the radically polymerised poly(N-phenylmaleimide) was studied, adopting the thermogravimetric method at heating rates of 1, 5, 10 and 50°C min−1 in a nitrogen atmosphere. The kinetic parameters, such as activation energy, reaction order, Arrhenius pre-exponential factor etc., have been calculated using different mathematical approximations available in the literature. It is observed that the energy of activation values and pre-exponential factors estimated for the degradation of poly(N-phenylmaleimide) from a single heating thermogram using different approximations decrease with increase in heating rate, whereas nearly constant values are observed in the Dharwadkar and Kharkhanavala approximation irrespective of the variation in sample size and heating rate. It is also observed that the different approximations, when applied to multiple heating data, give nearly constant values for the kinetic parameters. These values are broadly similar to that calculated using the Dharwadkar and Kharkhanavala approximation from a single heating thermogram.

PYROLYSIS MASS SPECTROMETRY OF HEXOLIC BASED POLYESTERS

Abstract Polyesters based on hexolic anhydride, hexolic-ethylene glycol (H-EG) and hexolic-1,4-butanediol (H-BD), have been synthesized for the first time by melt condensation in vacuum. Pyrolysis mass spectrometric studies have been done on these two polyesters at 300° C. From the mass spectral data, a plausible mechanism of degradation is proposed. To explain the different fragment ions formed during pyroly sis-electron impact, β-scissions in esters, acyl-oxygen and alkyl-oxygen bond homolysis, carbon-carbon bond scissions in the alkyl part of the glycol unit, pericyclic type reaction, McLafferty type rearrangement, retro Diels-Alder reaction, etc., have been invoked. In both the polyesters HCl is found to be one of the major products of pyrolysis. Further, the present study provides clues for the presence of ether linkages in the H-EG polyester.

Structural basis for intumescence – study of model compounds containing spiro phosphorus moiety and polymers containing such units

Spiro phosphorus compounds play a vital role, in recent years, in imparting flame retardancy and intumescence to the polymers. To ascertain the mechanism of the intumescency, model spiro phosphorus compounds, i.e., 3,9-disubstituted-2,4,8,10-tetraoxa-3,9-diphosphaspiro-[5,5]-undecan- 3,9-dioxide, were chosen (compound 1: substitution is chloro group and compound II: substitution is hydroxo group). The model compounds were investigated using Differential Thermal Analysis (DTA) and Thermal Volatilization Analysis (TVA), Vacuum Pyrolysis-MS and Off-line Pyrolysis followed by degradation product analysis by GC-MS. Dichlorospiro compound (I) showed an eruptive release of gases at 320 °C and dihydroxo spiro compound (II) at about 350 °C. The major components of the gas released were found to be HCl and H 2 O in the case of compound I and H 2 O in the case of compound II. The degradation product analysis showed the formation of wide varieties of substituted and condensed aromatic compounds in measurable quantities. From the acquired data, it is confirmed that the intumescence takes place within a narrow range of temperature (10°) and in this temperature limit extensive dehydrohalogenation and dehydration are taking place. Highly thermally reactive unsaturated hydrocarbons are produced which mainly undergo polymerization to aromatic compounds and finally to char.

A study of the thermal degradation behaviour of polyesters based on hexolic anhydride

Abstract The degradation behaviour of unsaturated polyesters containing hexolic anhydride has been studied. Pyrolysis experiments were performed using the TVA technique and the analysis of the products of pyrolysis was carried out utilising the gas chromatography-mass spectrometry technique. The formation of the various degradation products is discussed in the light of previously established mechanisms for polyester degradation. Special attention is devoted to a comparison of the present results on hexolic anhydride based polyesters with previously studied HET-acid based polyesters, which have similar structural characteristics in the chlorinated part of the molecule. The major degradation product from the hexolic moiety is hexolic anhydride. The degradation products resulting from the 1,4-butanediol components are similar for both hexolic- and HET-based polyesters. Contrary to the HET-acid based systems, the hexolic based polyesters yield considerably smaller quantities of hexachlorocyclopentadiene, which originates from the retro-Diels-Alder reaction.

Structural Basis for Intumescence – Part III – Thermal Degradation Study of Intumescent Polymers Containing Spirophosphorus Moiety in the Backbone

3,9-Dichloro-2,4,8,10-tetraoxo-3,9-disphosphaspiro-[5.5]-undecane-3,9-dioxide (spiro) was melt condensed with structurally different dihydric phenols to form poly aromatic spirophosphates. The thermal volatilization analysis showed eruptive release of gases above 300°C and the temperature region of release depends on the nature of the aromatic units incorporated in the polymer backbone. The thermal degradation in nitrogen atmosphere indicated the formation of phenol, substituted phenols, aromatics, alkyl and alkenyl substituted aromatics and condensed aromatics like azulenes, indanes and fluorenes. The source for the formation of these products is the spiropentadiene released from the spiro unit during degradation.

Structural characterization and thermal degradation of hexolic-anhydride-based polyesters

Abstract The structural characterization of the polyesters prepared by the melt condensation of hexolic anhydride with ethylene glycol and 1,4-butanediol was carried out using IR and 1 H and 13 C nuclear magnetic resonance (NMR) spectroscopies. From the thermogravimetric curves, the energy of activation for the degradation process was calculated by the method of Coats and Redfern. Flash pyrolysis-gas Chromatographie studies were performed at the temperatures 600 and 1000 °C. In contrast with similar polyesters based on 1,4,5,6,7,7-hexachloro -5-norbornene-2,3-dicarboxylic anhydride, the hexolic-anhydride-based materials yielded very low amounts of hexachlorocyclopentadiene during thermal degradation.

Thermal degradation of HET-acid based unsaturated polyester resins : a kinetic analysis of thermogravimetric data

Abstract The dynamic TG analysis of HET-acid based polyesters cured with styrene is presented. The Coats-Redfern analysis is applied.

Structural Basis for Intumescence—Part II: Synthesis and Characterization of Intumescent Polymers Containing Spirophosphorus Moiety in the Backbone

Taking the spirophosphorus compound 3,9-dichloro-2,4,8,10-tetraoxo-3,9-diphosphaspiro-[5,5]-undecane-3,9-dioxide as one of the reactive monomers, a family of aromatic spirophosphates was synthesized using dihydric phenols, viz., resorcinol, hydroquinone, 4,4′–dihydroxydiphenyl, bisphenol-A and fluorene dicarbinol as the other monomers. The polymers were synthesized employing melt condensation technique under vacuum and characterized using FT-IR, 1H-, 13C- and 31P-NMR spectroscopic methods. The number average molecular weight of the polymers was determined using vapour phase osmometry. Thermal properties of the polymers were studied using differential scanning calorimetry and thermogravimetry techniques. These studies indicated that the polymers containing spirophosphato moiety undergo eruptive degradations in the temperature region 310°–380°C leading to the formation of dense carbonaceous foam. The present study confirmed the spirophosphate structure as an essential requirement to show intumescence.

Effect of structure on the thermal degradation and flame retardancy of hexolic anhydride based polyesters

Based on the anhydrides like hexolic (5,6,7,8,10,10-hexachloro-3a,4,4a,5,8,8a,9,9a-octahydro-5,8-methanonaphtho-[2,3-c]-furan-1,3-dione), maleic and phthalic and diols like 1,4-butanediol, cis-2-butene-1,4-diol and 2,3-dichloro-2-butene-1,4-diol, a family of polyesters has been synthesized using azeotropic condensation technique. The structural characterizations of the polyesters have been carried out using infra-red, 1 H - and 13 C- nuclear magnetic resonance spectroscopic methods The thermal properties of the polyesters have been studied using thermogravimetric technique. The off-line pyrolysis of these materials was done The qualitative and semi-quantitative analyses of the volatiles as well as the heavy mass fractions of the degradation products were carried out using a gas chromatograph coupled to a mass selective detector (GC-MSD). Thermogravimetric data indicate that the thermal stability and the char residue of the polyester resins decrease in the order 1,4-butanediol based > cis-2-butene-1,4-diol based > 2,3-dichloro-2-butene-1,4-diol based polyesters. The GC-MSD data indicate that the amount of flame cooling agents (hexa-, isomeric penta-, tetra- and isomeric tri-chlorocyclopentadienes) produced during the pyrolysis of the polyesters increases in the order 2,3-dichloro-2-butene-1,4-diol based < cis-2-butene-1,4-diol based < 1,4-butanediol based polyesters. The trends observed in these two parameters which are contributing factors to the flame retardancy of the polyester materials were suitably explained on the basis of the effect of the structural changes in the diol part of the polyesters on the primary degradation mechanism, the β-chain scission process.