Pendant cyclodicarbaphosphazatriene-containing monomers and polymers: Synthesis, crystal structures and polymerization behavior

The reaction of the dicarbaphosphazene, [NC(NMe2)]2[NPCl2] (2), with the sodium salt of 4-hydroxy-4′-vinylbiphenyl afforded the vinyl group containing monomer [NC(NMe2)]2[NP(Cl)(O-C6H4-p -C6H4-p-CH=CH2)] (3). Replacement of the lone chlorine atom of 3 by oxygen nucleophiles gave [NC(NMe2)]2[NP(OR)(O-C6H4-p -C6H4-p-CH=CH2)] [R = CH2CF3 (4); C6H5 (5); C6H4-m-CH3 (6); C6H4-p-Br(7)]. The X-ray crystal structures of 3-7 reveal that all the cyclodicarbaphosphazenes have a planar N3PC2 ring; the ring carbons are completely planar, while the geometry around phosphorus is pseudotetrahedral. The presence of weak intermolecular hydrogen bonding {C-H---X(Cl or Br), C-H---N, or C-H---π} interactions in 3-7 leads to the formation of polymeric architectures in the solid-state. The monomers 4-7 can be polymerized by a free-radical initiator to afford the corresponding air-stable homopolymers 8-11. These have moderate molecular weights with polydispersity indices ranging from 1.33 to 1.58. All of these polymers have high glass transition temperatures and have excellent thermal stability.