In this study, the efficiency of several potential long lasting antiozonants was studied by ozonolysis of model olefins. 2-Methyl-2-pentene was selected as a model for natural rubber (NR) and 5-phenyl-2-hexene as a model for styrene butadiene rubber (SBR). A comparison was made between the efficiency of conventional antiozonants like N-(1,3 dimethylbutyl)-N-phenyl-p-phenylene diamine (6PPD), N-isopropyl-N-phenyl-p-phenylene diamine (IPPD), and a mixture of diaryl p-phenylene diamines (Wingstay 100) and some newly synthesized antiozonants. The stearic acid salt of 6PPD (PPD-C18), 2,4,6-tris(4-(phenylamino)phenyl)-1,3-5-triazinane (ADPAT), and 4-pyrole diphenylamine (PDPA) showed a higher efficiency than the conventional antiozonants in both NR as well as SBR model system. Special attention was paid to the carboxylic acid salts of 6PPD such as PPD-C18, which has shown good long-term protection of passenger tire sidewall compounds. It was demonstrated that by varying the chain length, C7, C18, and C22, of the carboxylic acid part of the 6PPD salts, the ozone protection was not influenced under the selected test conditions. The 6PPD salts made from strong acids like succinic acid (SA) and methyl sulfonic acid (MSA) appeared to be less efficient than PPD-C18. It was also investigated whether the reactions between ozone and the double bonds of the model rubber could be measured online by a spectroscopic technique. It was demonstrated that near infrared spectroscopy is a suitable technique to study these reactions. FT Raman looked also a promising technique because of the high response factor of double bonds. However, the addition of p-phenylene diamines (PPDAs) to the sample solution resulted in a strong discoloration (dark brown) and therefore in a high fluorescence background signal. This technique can therefore not be used for the evaluation of staining antiozonants.
- Differential scanning calorimetry (DSC)