Synthesis and pyrolysis of silicon and tin containing poly(2,2′-dioxy-1,1′-biphenoxy-phosphazenes)

The polyphosphazene {[NP(O2C12H8)]0.5[NP(OC6H4Br)2]0.5}n (1) [(O2C12H8) = 2,2′-dioxy-1,1′-biphenyl] that, as an strictly alternating copolymer, can be considered nearly as the homopolymer [NP(O2C12H8)NP(OC6H4Br)2]n, was reacted first with tBuLi in THF at −78 °C to give the intermediate [NP(O2C12H8)NP(OC6H4Li)2]n (2) and subsequently with the chlorosilanes SiMe3Cl and SiMe2(C6H5)Cl or with the chlorostannane SnMe3Cl, to obtain the new polyphosphazenes {(NP[O2C12H8])0.5[NP(OC6H4SiMe3)2]0.5−x[NP(OC6H5)(OC6H4SiMe3)]x}n (3a) (x = 0.15–0.5), {(NP[O2C12H8])0.5[N(POC6H4SiMe2Ph)2]0.2[NP(OC6H5)(OC6H4SiMe2Ph)]0.3}n (3b), and {(NP[O2C12H8])0.5[NP(OC6H5)(OC6H4SnMe3)]0.5}n (4), having a very regular distribution of the silicon or tin organometallic sites along the chains. The pyrolysis of the polymers in air at 800 °C gave microcrystalline residues (characterized by IR, XRD, SEM and TEM-EDXA) consisting on phases of SiO2 · P2O5 · P2O7.9 · SiP2O7, or, in the case of the tin derivative, almost pure SnP2O7. The results indicate that, while part of the Si content is lost during the pyrolysis, almost all the tin in the original polymer was incorporated to the final residue.