New combined phenol/hindered amine photo- and thermal-stabilizers based on toluene-2,4-diisocyanate

Abstract

Reactions of toluene-2,4-diisocyanate with different phenols and different HAS (hindered amine stabilizers) were used to prepare new combined phenol/HAS. As a phenol 2- tert-butyl-4-methoxyphenol ( I); 2- tert-butyl-4-methylphenol ( II); 2,4-di- tert-butyl-6-methylphenol ( III) and 2,4-di- tert-butylphenol ( IV) were used. HAS represented 4-hydroxy-2,2,6,6-tetramethylpiperidine ( TMP), 4-hydroxy-1,2,2,6,6-pentamethyl-piperidine ( PMP), 4-amino-2,2,6,6-tetramethylpiperidine (ATP), 4- N-butyl-amino-2,2,6,6-tetramethyl-piperidine ( BATP) and 4-hydroxy-2,2,6,6-tetramethylpiperidin- N-oxyl ( TMP-NO ·). Symmetrical phenol–phenol and HAS–HAS were also prepared. The synthesized compounds were tested as light and thermo stabilizers in polypropylene (PP). Non-oxidized as well as partially oxidized PP was used. The stabilizing efficiency depends on the structure of the phenol as well as the HAS. Concerning the phenol structure the best efficiency at photo oxidation was obtained with combined phenol/HAS containing 2,6-disubstituted phenol III for all HAS used. Efficiencies of phenols with just one substituent in the ortho position in combined additives were much lower. This difference was rather small in the case of thermo oxidation. Among the HAS the best performance was obtained from derivatives of TMP and PMP in photo oxidation of non-oxidized PP matrix. PMP derivatives in contrast to TMP ones did not stabilized partially oxidized PP very well. The efficiency of combined phenol/HAS was much higher than the efficiency of symmetrical HAS/HAS despite two times higher concentration of the active part in the symmetrical molecules. All combined additives showed very good ability to stabilize PP against thermo-oxidation. The highest efficiency was reached with TMP derivatives—about 12 000 to 14 000 h to reach carbonyl absorption 0.2 at 110 °C.