Abstract
N-alkyl phosphoranimines were synthesized via the Staudinger reaction of four different alkyl azides with tris(2,2,2-trifluoroethyl) phosphite. N-adamantyl, N-benzyl, N-t-butyl, and N-trityl phosphoranimines were thoroughly characterized and evaluated as chain-capping compounds in the anionic polymerization of P-tris(2,2,2-trifluoroethoxy)-N-trimethylsilyl phosphoranimine monomer. All four compounds reacted with the active chain ends in a bulk polymerization, and the alkyl end groups were identified by 1H-NMR spectroscopy. These compounds effectively controlled the molecular weight of the resulting polyphosphazenes. The chain transfer constants for the monomer and N-benzyl phosphoranimine were determined using Mayo equation.
Highlights
IntroductionThe field of polyphosphazene synthesis has expanded significantly with the advent of more efficient and faster synthetic routes such as the ambient temperature preparation of poly(dichlorophosphazene) by the PCl5 -initiated polymerization of N-trimethylsilylP-trichlorophosphoranimine, [13,19] the polymerization of N-trimethylsilyl-P-tris(2,2,2trifluoroethoxy)phosphoranimine by antimony pentachloride initiator, [20] and poly (organophosphazenes) from partially halogenated phosphoranimines [21]
The synthetic route to the four N-alkyl phosphoranimines prepared in thisanionic study was forming polymer can react with a monomer molecule via chain growth condensation (with via the Staudinger reaction [43] is shown in Scheme 2, in which tris(2,2,2-trifluoroethyl) elimination of trimethylsilyl trifluoroethoxide), or it may react with a partially polymerized phosphite reacted with an alkyl azide to form the P-tris(2,2,2-trifluoroethoxy)-N-alkyl chain segment to advance molecular weight via a macrocondensation
We report more detailed experimental data obtained using these compounds, and present evidence of their incorporation as unique chain end groups during the formation of polyphosphazenes by the anionic route
Summary
The field of polyphosphazene synthesis has expanded significantly with the advent of more efficient and faster synthetic routes such as the ambient temperature preparation of poly(dichlorophosphazene) by the PCl5 -initiated polymerization of N-trimethylsilylP-trichlorophosphoranimine, [13,19] the polymerization of N-trimethylsilyl-P-tris(2,2,2trifluoroethoxy)phosphoranimine by antimony pentachloride initiator, [20] and poly (organophosphazenes) from partially halogenated phosphoranimines [21]. These reactions are examples of cationic polymerization of phosphoranimines. The cationic route has led to polyphosphazenes with functional and terminal groups at the chain ends [22,23,24,25,26,27]
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