Nitration Study of Cyclic Ladder Polyphenylsilsesquioxane

Several nitration reagents including fuming nitric acid, HNO₃-H₂SO₄, KNO₃-H₂SO₄, HNO₃-KNO₃, CH₃COOH-KNO₃, (CH₃CO)₂O-HNO₃ were used to nitrate cyclic ladder polyphenylsilsesquioxane (CL-PPSQ) in different conditions in order to enhance the compatibility of the CL-PPSQ in polymers, the NO₂-PPSQ was obtained. FTIR, element analysis, GPC, TGA and ¹H NMR were used to characterize the structures of the nitrated products. The results show that the nitrating abilities of the fuming nitric acid, HNO₃-H₂SO₄ and KNO₃-H₂SO₄ are very strong. Many nitro groups can be linked with phenyl groups in CL-PPSQ, but with low molecular mass, fracture occurs in siloxane segment. However, the M_n of the product NO₂-PPSQ sharply drops by 50% compared with that of CL-PPSQ, so the nitration reagents can break the cyclic structure of CL-PPSQ. The nitrating reagents of HNO₃-KNO₃ and CH₃COOH-KNO₃ have no nitration effects on CL-PPSQ. At last, NO₂-CL-PPSQ was prepared using (CH₃CO)₂O-HNO₃ because of the moderate nitration process and ability. The cyclic structure of PPSQ is remained, although the number of-NO₂ group is not too much. At the same time, the nitration mechanism using different nitration reagents was analyzed. A certain amount of NO₂⁺, which is a kind of activator owning strong nitration ability, can be found in the fuming nitric acid and H₂SO₄-HNO₃(KNO₃) systems. As to the (CH₃CO)₂O-HNO₃ system, the main activator is CH₃COONO₂.