Control of End Groups in Anionic Polymerizations Using Phosphazene Bases and Protic Precursors As Initiating System (XH-Bu^<i>t</i>P₄ Approach): Application to the Ring-Opening Polymerization of Cyclopropane-1,1-Dicarboxylates

Abstract

A synthetic method involving the in situ generation of an anionic initiator X− obtained by reaction of its conjugate acid precursor XH with ButP4 phosphazene base was tested as a possible way to easily and better control the end groups of polymers derived from the anionic ring-opening polymerization of cyclopropane-1,1-dicarboxylates. Several types of precursors were investigated, including thiols, alcohols, a carbazole, and a malonate. In all but one cases, a living polymerization mechanism could be observed, which was exploited to control the nature of the terminal end groups by reaction of the propagating malonate carbanion R−C(COOPr)2− with alkylating agents. It was also demonstrated that toluene was a much better solvent than the traditional one used in these reactions (THF) as a larger range of available temperatures was available despite an almost identical solvent influence on the polymerization. Exploitation of this feature provided access to higher degrees of polymerization than previously possible.