ANIONIC RING-OPENING POLYMERIZATION OF 1,1,3-TRIMETHYL-1-SILACYCLOPENT-3-ENE - EFFECT OF TEMPERATURE ON POLY(1,1,3-TRIMETHYL-1-SILA-CIS-PENT-3-ENE) MICROSTRUCTURE

1,1,3-Trimethyl-1-silacyclopent-3-ene (I) undergoes anionic ring-opening polymerization on treatment with n-butyllithium and HMPA cocatalysts in THF to yield poly(1,1,3-trimethyl-1-sila-cis-pent- 3-ene) (II). Comparison of1H,13C, and29Si NMR spectra of II with those of model compounds, (Z)- and (E)-2-methyl-1,4-bis(trimethylsilyl)-2-butene (IV), permits assignment of polymer II microstructures. When the polymerization of I is conducted at -42 °C, the NMR spectra of II are consistent with a polymer in which cis-1,4-isoprene units are joined to dimethylsilylene units. A 1:2:1 distribution of head-to-head, head- to-tail, and tail-to-tail arrangements of adjacent cis-1,4-isoprene units is found. On the other hand, when the polymerization is conducted at -78 °C, the microstructure of II is predominantly head-to-tail. The mechanism of polymerization, which may account for the observed regioselectivity, is discussed. © 1990, American Chemical Society. All rights reserved.