N-(substituted phenyl)itaconimides as organic stabilizers for rigid poly(vinyl chloride) against thermal degradation

Several N-(substituted phenyl)itaconimide derivatives, N-(RPh)II, (R:-NO2, -COOH, -H, -OH, -OMe, -Me, -Cl or -Br) have been investigated as organic thermal stabilizers for rigid poly(vinyl chloride) (PVC) at 180 degreesC in air. Their stabilizing efficiencies are evaluated by measuring the length of the induction period (T-s), the period during which no detectable amounts of hydrogen chloride gas could be observed, and also from the rate of dehydrochlorination as measured by continuous potentiometric determination on one hand, and the extent of discoloration as well as the change in the mechanical properties of the degraded polymer on the other. Their stabilizing efficiencies were compared with that of dibasic lead carbonate (DBLC), barium-cadmium-zinc stearate (Ba-Cd-Zn stearate) and n-octyltin mercaptide (n-OTM), which are commonly used industrial stabilizers. The results clearly reveal the greater stabilizing efficiency of almost all the N-(RPh)II derivatives except those of the nitro-derivatives as compared with industrially used thermal stabilizers. This is well illustrated by the longer T-s values, and by the lower rates both of dehydrochlorination and discoloration as well as mechanical properties loss of the polymer during degradation relative to those of the reference stabilizers. The results also demonstrate how the stabilizing efficiency is affected both by the nature and position of the substituents in the phenyl ring of the itaconimide stabilizers. Thus, while N-(RPh)II derivatives with groups of positive resonance effect (+R) show higher values of T-s and lower rates of dehydrochlorination relative to those having groups of negative resonance effect (-R), the unsubstituted N-PhII lies between these two extremes. The stabilizing efficiency of N-(R-Ph)II derivatives is attributed to the replacement of the labile chlorines on the PVC chains by relatively more thermally stable stabilizer moieties. A radical mechanism for the stabilizing action of the investigated stabilizers is suggested. A synergistic effect is achieved when the materials under investigation were blended in various molar ratios with either of the reference stabilizers. This synergism attains its maximum when both the investigated and the reference stabilizers are taken in equivalent molar ratios. (C) 2002 Elsevier Science Ltd. All rights reserved.