Anionic ring-opening polymerization exchange reaction

Anionic ring-opening polymerization of POx initiated by partially deprotonated dipropyleneglycol (DPG) in the presence of the phosphonium cation tetrakis[cyclohexyl(methyl) amino jphosphonium as counterion (P Scheme 14) has been reported by Rexin and Miilhaupt. An alcohol/phospho-nium alkoxide mixture (95/5) was utilized to control reactivity, making use of a fast proton exchange reaction between dormant hydroxy compounds and active phosphonium alkoxide ends (Scheme 16). 

Summary Phosfdiazene bases represent a new class of highly active non-ionic catalysts that rapidly polymerize cyclosiloxanes with equilibrium attained in very short reaction times at very low catalyst levels. To date, phosphazene base catalysts have been considered an academic curiosity because of the complicated and hazardous synthetic protocol used to prepare them. A facile synthetic process has been developed, which yields ionic phosphazene bases in three steps with an overall yield of qrproximately 75%. This is achieved through nucleophilic substitution of ionic phosphonitrilic chloride oligomers with secondary amines, followed by anion exchange. These ionic phosphazenes were found to exhibit similar reactivity in the ring-opening polymerization of cyclosiloxanes to that of the non-ionic phosphazene base. 

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