New Antiozonants for Rubber Protection Based on Derivatives of a Naturally Occurring Molecule: Camphor

Abstract

Two new antiozonant molecules (for diene rubber compounds) have been synthesized using (1R,4R)(+)-camphor as key raw material derived from the renewable source Cinnamomum camphora tree. The diimine reaction product of p-phenylenediamine (p-PPD) and two molecules of camphor was reduced in situ with NaBH₄, yielding N,N′-dicamphyl-p-phenylenediamine (2Cam-PD). Similarly, the imine reaction intermediate between ADPA (4-aminodiphenylamine) and one molecule of camphor was reduced in situ, producing N-camphyl-N′-phenyl-p-phenylenediamine (Cam-PPD). The two new antiozonants were characterized by FT-IR spectroscopy and by DSC analysis in comparison to the diimine (2Cam-PD-diimine) and imine (Cam-PPD-imine) intermediates, respectively. DSC analysis was also made on the starting reagents p-PPD, ADPA, and (1R,4R)(+)-camphor. The properties of 2Cam-PD and Cam-PPD are discussed in comparison to the currently used antiozonants. Particular emphasis is addressed toward the analogies of 2Cam-PD with the “safe” antiozonant CCPD (N,N′-dicyclohexyl-p-phenylenediamine) and Cam-PPD with CPPD (N-cyclohexyl-N′-phenyl-p-phenylenediamine). The raw material fraction derived from the renewable source is 73.8% for 2Cam-PD and 45.2% for Cam-PPD.