The formation and significance of polyconjugated systems in thermal and thermo-oxidative processes

Abstract

The processes of formation of polyconjugatcd fragments during thermal oxidation of polymers and the reactions of low molecular compounds yielding polymers with an extended system of conjugation are considered. It is shown from the experimental data that the polyconjugated system (PCS) formed during thermal oxidation and thermolysis exerts initiating or activating action during the process. The cause of such properties of the PCS is the existence in macromolecules of stable biradicals capable of complex formation with diamagnetic molecules. in this complex the radical reactivity is enhanced due to an increased probability of ST transfer (effect of local activation). Initiation of hydroperoxide decomposition caused by the PCS explains the high synergetic action of mixtures of polyconjugated polymers formed during thermal oxidation or thermolysis of monomeric inhibitors (bisphenols, aromatic amines, etc.) and initial monomers not subjected to such treatment. It is shown that during thermolysis along with paramagnetic centres (PMC), the active radicals are formed due to the rupture of valence bonds. These a-radicals stabilized by a rigid matrix diminish the thermal-oxidative stability when molecular mobility is 'frozen'. The activity of a-radicals, under proper conditions, can suppress the inhibiting effect of stable PMC complexes and cause transition from oxidation to burning. The probability of purposeful regulation of PCS action is associated with the information about the PMC formation mechanism during the growth of polyconjugated chain. The author's attitude concerning the existence of paramagnetic branched chains resulting from local ic-bonds unpairing in PCS is considered. Due to this fact a paramagnetic avalanche is formed because of ST transition activation in a complex with other macromolecules by PMC formed during the preceding step. The advanced theory is in excellent agreement with known experimental data and may be useful for interpretation and prediction of the results of future investigations. By means of thermodynamic calculations it is easy to show that in many cases the propagation of a polyconjugated chain is the most probable process in the thermal and thermo-oxidative destruction of organic compounds1. The reason for this is connected with the decrease in internal energy for the transition from 'saturated' compounds to substances with a system of