SYNTHESIS AND THERMAL AND PHOTOOXIDATIVE BEHAVIOR OF NOVEL AMINATED 2-HYDROXYBENZOPHENONE STABILIZERS IN POLYOLEFIN FILMS

Three light stabilizers have been prepared and characterized, based on the substitution of a tertiary amine group into the 3- and 5-positions of 2,4-dihydroxybenzophone (DHBZ) and 2-hydroxy-4-n.octoxybenzophenone (HOBZ) via the Mannich reaction. The derivatives prepared by this method were, the 3-N,N-diethylaminomethyl of the former and the 5-N,N-diethylaminomethyl and 5-morpholinomethyl derivatives of the latter. The thermal and photo-oxidative stabilization activities of the three compounds have been examined and compared with those of DHBZ and HOBZ in medium density polyethylene and polypropylene films at 0.1% w/w concentration using i.r. absorption and fluorescence spectroscopy and hydroperoxide analysis. In medium density polyethylene, all three aminated derivatives are weak antioxidants with the diethylaminomethyl derivative of DHBZ being the most effective. The commercial light stabilizers DHBZ and HOBZ were also weak antioxidants but less effective than the aminated derivatives. In polypropylene, similar results were obtained but in this case both the Mannich derivatives of HOBZ were effective. In the presence of a hindered phenolic antioxidant, Irganox 1010, all the stabilizers except the HOBZ were synergistic in the thermal oxidation of polyethylene whereas in polypropylene the effects were antagonistic. On photo-oxidation, the effects were reversed with antagonism being observed in the case of polyethylene and synergism in polypropylene but only in the case of the morpholinomethyl derivative of HOBZ. Surprisingly, the three aminated derivatives were less effective as light stabilizers than the two simple commercial benzophenone stabilizers HOBZ and DHBZ. Hydroperoxide formation is markedly reduced on oven-ageing of polypropylene by the aminated derivatives and is consistent with the ability of the tertiary amine group to scavenge oxygen and free radicals. Fluorescence quenching studies on the same polymer also show that the aminated derivatives are more effective quenchers than the corresponding commercial HOBZ and DHBZ stabilizers.