Synthesis of Poly(alkyl/arylphosphazenes) via the Ambient Temperature Phosphite-Mediated Chain-Growth Polycondensation of (<i>N</i>-Silyl)bromophosphoranimines

The room temperature addition of stoichiometric amounts of trimethyl phosphite, P(OMe) 3, to N -silyl(halogeno)organophosphoranimines BrRR′P═NSiMe 3 in chlorinated solvents led to the direct formation of high molecular weight polyphosphazenes [RR′P═N] n . The majority of polymerizations were complete within 18 h. The polymers prepared include poly(dialkylphosphazenes) (e.g., [ n Bu 2 P═N] n 1b ), poly(alkylarylphosphazenes) (e.g., [PhMeP═N] n 1d ), new materials featuring unsaturated substituents (e.g., [ n Hex{H 2 C═C(H)CH 2 }P═N] n 1n ), and random copolymers (e.g., {[PhMeP═N] x −[Ph n BuP═N] y } where x: y = 2:1, 7a ). The precursor silylaminophosphines RR′P−N(SiMe 3 ) 2 ( 5a − q ) and bromo(silylamino)phosphoranimines BrRR′P═NSiMe 3 ( 4a − q ) were synthesized and fully characterized prior to polymerization studies. The presence of alkoxy, carboranyl, and/or phenyl substituents on the N -silylbromophosphoranimines, as found in BrEt[CF 3 CH 2 O]P═NSiMe 3 ( 4g ), Br(2-[Me]- o -C 2 B 10 H 10 )EtP═NSiMe 3 ( 4h ), or BrPh 2 P═NSiMe 3 ( 4i ), respectively, was found either to severely retard or to preclude polymerization altogether. The mild reaction conditions enabled the preparation of polyphosphazenes that are substituted with reactive alkyne groups (e.g., R = Et, R′ = −CH 2 C≡CSiMe 3 1p ), materials that have not been accessible using high-temperature thermal routes. These moieties undergo further convenient chemical transformations as illustrated by deprotection of 1p by TBAF·3H 2 O (TBAF = tetra( n -butyl)ammonium fluoride) as well as chemical cross-linking with the disiloxane HMe 2 SiOSiMe 2 H in the presence of Karstedt’s catalyst. The polyphosphazene materials were characterized by a variety of techniques including 1 H, 13 C, and 31 P NMR spectroscopy and GPC and, in selected cases, by IR, DLS, TGA, DSC, and WAXS.

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