Solid State 13C-NMR Analysis of Syndiotactic Copolymers of Propene with 1-Butene

An analysis of the structure of syndiotactic copolymers of propene with l-butene prepared with a single-center metallocene-based catalyst in a whole range of comonomer composition, by solid state C-13 NMR CPMAS spectroscopy, is presented. The presence of resonances of carbon atoms of butene and propene units in the spectra of all copolymers, with intensities depending on the composition, possibly indicates the inclusion of the comonomeric units in the unit cells of both homopolymers. The splitting of the resonance of methylene carbon atoms in conformational environment TG.GT of propene units in propene-rich copolymers has been explained by a conformational effect, assuming that the butene units, included in the crystalline phase of syndiotactic polypropylene, produce a slight distortion of the local conformation close to the comonomeric units. The presence of additional signals at approximate to 35 and approximate to 45 ppm, attributed to the resonances of backbone GT.TG and TG GT methylene carbon atoms, respectively, located at interfaces between propene (P) and butene (B) units, i.e. belonging to PB sequences, has been explained assuming that also in isolated butene units the lateral ethyl groups assume the "double" gauche conformation, typical of the chains of form I of syndiotactic poly(1-butene). (C) 1999 Elsevier Science Ltd. All rights reserved.