Anionic ring‐opening polymerization of cyclodisilazanes, 3. Influence of the silicon substituent on the kinetics of polymerization

Abstract

AbstractThe kinetics of the anionic ring‐opening polymerization of several cyclodisilazanes substituted with different groups on silicon atoms has been investigated in toluene/tetrahydrofuran (THF) using benzyllithium as initiator. Two different behaviours were observed: for hindered substituents (phenyl or allyl), the polymerization is not living; for less hindered groups, the polymerization is living but the rate constants differ markedly from one cyclodisilazane to another. They vary from 9 × 10−4 L · mol−1 · s−1 for DNMeEtDNMe 3 to 0,1 L · mol−1 · s−1 for DDNMe (8). These variations show that the presence of vinyl groups on the monomers tremendously increases the rate of polymerization. In order to discriminate the monomer reactivity from the active center reactivity, a model reaction between lithium silylamides and triethylchlorosilane has been kinetically studied (each lithium silylamide was chosen to modelize one particular active center). Contrary to the corresponding monomers, the less hindered is the silylamide, the faster is the reaction. Thus, the difference of reactivity between the monomers and the reactive center models is so high that the polymerization of cyclodisilazanes can be considered as principally controlled by the reactivity of the monomers.