Solid state C-13 NMR analysis of syndiotactic copolymers of propene with 1-butene

An analysis of the structure of syndiotactic copolymers of propene with l-b utene prepared with a single-center metallocene-based catalyst in a whole r ange of comonomer composition, by solid state C-13 NMR CPMAS spectroscopy, is presented. The presence of resonances of carbon atoms of butene and prop ene units in the spectra of all copolymers, with intensities depending on t he composition, possibly indicates the inclusion of the comonomeric units i n the unit cells of both homopolymers. The splitting of the resonance of me thylene carbon atoms in conformational environment TG.GT of propene units i n propene-rich copolymers has been explained by a conformational effect, as suming that the butene units, included in the crystalline phase of syndiota ctic polypropylene, produce a slight distortion of the local conformation c lose to the comonomeric units. The presence of additional signals at approx imate to 35 and approximate to 45 ppm, attributed to the resonances of back bone GT.TG and TG GT methylene carbon atoms, respectively, located at inter faces between propene (P) and butene (B) units, i.e. belonging to PB sequen ces, has been explained assuming that also in isolated butene units the lat eral ethyl groups assume the "double" gauche conformation, typical of the c hains of form I of syndiotactic poly(1-butene). (C) 1999 Elsevier Science L td. All rights reserved.