The Solid State sup (29) Si and sup (13) C NMR of Poly(di- n-alkylsilanes).

(A chapter in an ACS Advances in Chemistry Series, representing a contribution to the Symposium on Solid State NMR of Polymers at the North American Chemical Congress, sponsored by the Division of Polymer Chemistry of the American Chemical Society; Toronto, June 6-9, 1988.) Poly(di-n-hexylsilane) is composed of a crystalline phase (I) in which the silicon main chain has an all-trans or planar zigzag conformation, together with a less ordered phase (II) in which non-trans conformations are present. The solid state sup (29) Si NMR spectrum exhibits two resonances, the more shielded of which corresponds to Phase II. A I -> II transition occurs at 40degrees-42C, above which only the more shielded sup (29) Si resonance is observed. The sup (13) C spectra are consistent with the disordering of the sidechains in Phase II. The Phase I sup (13) C resonances exhibit a doubling which is not at present understood. Poly (di-n-pentylsilane) and poly(di-n- -butylsilane) exhibit I -> II transitions at 70degrees and 87degrees, respectively. Their sup (29)Si spectra show strikingly different behavior from that of the poly(di-n-hexylsilane). The crystalline phase (I) shows a more shielded resonance than that of the disordered phase. This is consistent with the X-ray findings of a 7/3/ helical backbone bond arrangement. The phase I sup (13) C spectrum of poly(di-n-butylsilane) shows peak doubling similar to that of the dihexyl polymer.