The Controlled and Regioselective Macromolecular Nitration of Poly(2,2'-dioxy-1,1 '-biphenylphosphazene) in Concentrated Sulfuric Acid

The polyphosphazene [NP(O 2 C 12 H 8 )] n (1) [(O 2 C 12 H 8 ) = 2,2'-dioxy-1,1'-biphenyl] was reacted with different molar ratios of 65% aqueous HNO 3 (or with LiNO 3 ) in concentrated (98%) sulfuric acid under different experimental conditions to give the nitrated polymers 5,5'-3,3'-{NP[02C 12 H 8-x (NO 2 ) x ]} n (2) (x = 0.2 to 2) opening the route to further functionalization of (1) directly in the dioxy-biphenyl-phosphorus cyclic units. The reaction was not perfectly randomized and was not regiospecific but showed high regioselectivity in favor of the 5,5' positions. The glass transitions of the products (in the range 161-238 °C) showed a linear dependence with the NO 2 contents evidencing the lack of chemical regularity along the chains. The TGA thermograms of the nitrated polymers showed that the decompositions were faster the higher the NO 2 contents leaving less final residue at 800 °C, demonstrating the destabilizing effects of the NO 2 on the polyphosphazene. Various attempts to reduce the NO 2 groups to NH 2 are also described.