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The kinetics of the anionic ring-opening polymerization of several cyclodisilazanes substituted with different groups on silicon atoms has been investigated in tolueneketrahydrofuran (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 x lo4 L -mol-' -s-' for PAeDNMe 3 to 0,l L * mol-' -s-' for DiEeDNMe (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.

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The kinetics of ring‐opening metathesis polymerization of norbornene were investigated in cyclohexane using several Schrock complexes as initiators. Three different Schrock complexes were used: Mo(CHC(CH3)2Ph)(NAr)(O‐t‐Bu)2 (NAr = Ph (iPr) 2) (I), Mo(CHC(CH3)2Ph)(NAr)(OC(CF3)2CH3)2 (NAr = Ph (iPr) 2) (II) and W(CH‐t‐Bu)(NAr)(O‐t‐Bu)2 (NAr = Ph (iPr) 2) (III). The presence of alkoxy‐fluorinated ligands on II and on the corresponding propagating species enhances the polymerizability of norbornene and modifies the kinetic scheme compared to that of polymerizations initiated by the tert‐butoxy complex. The greater electropositive character of II compared to that of I results in a majority of metalla‐alkylidenic growing species being complexed to monomer; therefore, the coordination of the monomer is not the rate‐determining step for the process. In contrast, the major part of growing species, which are derived from the tert‐butoxy complex are in a non‐coordinated state and, thus, the ability of the initiator to complex the monomer is decisive. In addition, this study allows to quantify the stronger reactivity of W‐based complexes compared to that of Mo‐based ones. These results were all corroborated by prior theoretical studies using ab initio calculations.