Biologically active maleimido aromatic 1,3,4-oxadiazole derivatives evaluated thermogravimetrically as stabilizers for rigid PVC

摘要

Four novel N-aryl maleimide-bearing aromatic 1,3,4-oxadiazole systems were synthesized via a thermally induced cyclodehydration reaction of their corresponding precursors maleimido aromatic hydrazide derivatives. Their chemical structures were confirmed by elemental analyses, FTIR, H-1-NMR and mass spectroscopy. They showed a good antimicrobial activity against Bacillus subtilis, Streptococcus pneumoniae, Escherichia coli, Aspergillus fumigatus, Geotrichum candidum and Syncephalastrum racemosum using agar well diffusion method. The investigated derivatives are thermally stable and start decomposition in the temperature range above 250-300 A degrees C. They were investigated for thermal stabilization of rigid PVC using thermogravimetric analysis technique, in nitrogen. They showed a greater stabilizing efficiency as illustrated by their higher initial decomposition temperature and higher residual mass percent at particular temperatures relative to dibasic lead carbonate, cadmium-barium-zinc stearate complex and di-n-octyltin bis (isooctylmercaptoacetate) (n-octyltin mercaptide, n-OTM) reference thermal stabilizers. Their stabilizing efficiency is also demonstrated by lower rates of both discoloration and degree of chain scission of the polymer during degradation. The electron-donating substituent groups in the aromatic ring of 1,3,4-oxadiazole part of these derivatives increased their stabilizing efficiency.