title: A cooperative role for the counteranion in the PCl5-initiated living, cationic chain growth polycondensation of the phosphoranimine Cl3P═NSiMe3.
abstract: The counteranion associated with the cationic initiator [Cl(3)P═N═PCl(3)](+) ([4](+)) generated during the PCl(5)-initiated living, cationic chain growth polycondensation of the N-silylphosphoranimine Cl(3)P═NSiMe(3) (3) to give poly(dichlorophosphazene), [N═PCl(2)](n) (2), has been found to have a dramatic effect on the polymerization. When the counteranion of [4](+) was changed from PCl(6)(-) or Cl(-) to the weakly coordinating anions [BAr*(F)(4)](-) and [BAr(F)(4)](-) (Ar*(F) = 3,5-{CF(3)}(2)C(6)H(3), Ar(F) = C(6)F(5)) instead of the polymerization of 3 being complete in 4-6 h, no reaction was observed after 24 h. Remarkably, the polymerization of 3 may be initiated by Cl(-) anions even in the absence of an active cation such as [4](+). However, in the presence of [4](+), the reaction proceeded significantly faster and allowed for molecular weight control. These results reveal that the currently accepted mechanism for the PCl(5)-initiated living polymerization of 3 needs to be revised to reflect the key role of the counteranion present.
authors.affiliation: School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, UK.
authors.forename: Vivienne
authors.initials: V
authors.lastname: Blackstone
authors.forename: Stefan
authors.initials: S
authors.lastname: Pfirrmann
authors.forename: Holger
authors.initials: H
authors.lastname: Helten
authors.forename: Anne
authors.initials: A
authors.lastname: Staubitz
authors.forename: Alejandro
authors.initials: A
authors.lastname: Presa Soto
authors.forename: George R
authors.initials: GR
authors.lastname: Whittell
authors.forename: Ian
authors.initials: I
authors.lastname: Manners