The thermolytic behaviour of trimethylsilyl trifluoromethanesulfonate, 1, trimethylsilyl trifluoroacetate, 2, and trimethylsilyl acetate, 3, has been investigated by ultraviolet photoelectron spectroscopy. Acetate 3 undergoes decomposition only to a small extent at 800 °C via the mechanism shown in Scheme 1 (X = Si); only acetic acid and starting material are detected. In contrast[Formula: see text]with this result, 1 and 2 decompose completely at 725–800 °C and yield products which cannot be derived via the mechanism shown in Scheme 1. Evidence is presented to support our proposal that the thermolysis of 1 yields trimethylsilyl fluoride, 6, and difluorooxathirane dioxide, 7, as primary products. The photoelectron spectra of 1, 2, 3, 6 and trimethylsilanol, 9, are presented. Molecular orbital eigenvalues of dimethylsilene, 4, dimethylsilanone, 5 (calculated using AMPAC and Gaussian 82), 6 and 9 (AMPAC) are reported. Molecular orbital contour diagrams are given for selected MOs of 6 and 9.

Under cationic conditions using triflic acid as the initiator, it is possible to oligomerize Ptrichlorosilylstyrene 2 to low molecular weight oligomers 14 with a maximum degree of polymerization of about 9. Termination of the process was shown to occur by an intramolecular FriedelLCrafts reaction, leading to highly functionalized, indane-terminated oligomers 9, 12, etc. At lower temperatures, the reaction is diastereoselective. The oligomerization process was shown to require electron-withdrawing groups on silicon; the replacement of C1 spectator ligands with alkoxy or alkyl groups led to protiodesilylation. The mechanism for formation of the indane-terminated oligomers is discussed.Key words: cationic polymerization, P-silylstyrene, stereoselective oligomerization, indene termination.RCsumC : Sous des conditions cationiques utilisant de l'acide triflique comme initiateur, il est possible de provoquer une oligomCrisation du P-trichlorosilylstyrkne, 2, en oligomkres 14 de bas poids molCculaire et comportant un degrC maximal de polymCrisation d'environ 9. On a montrC que le processus de terminaison se produit par une rCaction de FriedelLCrafts intramolCculaire conduisant B des oligomkres 9,12, etc. se terminant par des indanes hautement fonctionnalisCs. A des tempkratures plus basses, la rCaction est diastCrCosClective. On a montrC que le processus dLoligomCrisation nCcessite la presence de groupes Clectroattracteurs sur le silicium; le remplacement des coordinateurs C1 agissant comme spectateurs par des groupes alkoxyles ou alkyles conduit t i une protiodCsilylation. On discute du mecanisme de formation des oligomkres se terminant par un indane.Mots clks : polymCrisation cationique, P-silylstyrkne, oligomCrisation stCrCosClective, terminaison par un indkne.[Traduit par le rCdaction]