ANIONIC RING-OPENING POLYMERIZATION OF CYCLODISILAZANES .3. INFLUENCEOF THE SILICON SUBSTITUENT ON THE KINETICS OF POLYMERIZATION

The kinetics of the anionic ring-opening polymerization of several cyc lodisilazanes substituted with different groups on silicon atoms has b een investigated in toluene/tetrahydrofuran (THF) using benzyllithium as initiator. Two different behaviours were observed: for hindered sub stituents (phenyl or allyl), the polymerization is not living; for les s hindered groups, the polymerization is living but the rate constants differ markedly from one cyclodisilazane to another. They vary from 9 x10(-4) L . mol(-1) . s(-1) for (DNMeDNMe)-D-Et 3 to 0,1 L . mol(-1) . s(-1) for (DNMeDNMe)-D-2Vi (8) These variations show that the presenc e of vinyl,stoups on the monomers tremendously increases the rate of p olymerization. In order to discriminate the monomer reactivity from th e active center reactivity, a model reaction between lithium silylamid es and triethylchlorosilane has been kinetically studied (each lithium silylamide was chosen to modelize one particular active center). Cont rary to the corresponding monomers, the less hindered is the silylamid e, the faster is the reaction. Thus, the difference of reactivity betw een the monomers and the reactive center models is so high that the po lymerization of cyclodisilazanes can be considered as principally cont rolled by the reactivity of the monomers.