Experimental evidence for the regiospecific primary mode of styrene insertion into metal‐carbon bonds of an isospecific Ziegler‐Natta catalyst

Abstract

StyreneA-hexene copolymers of different chemical composition were prepared with a classical isospecific Ziegler-Natta catalyst, TiCh(H)-AlE+. Their structure and the distribution of the monomeric units was analyzed by GPC double detection and 'H and 13C NMR. The chemical arrangement of isolated and blocked styrene monomeric units between sequences of hexene monomeric units was also investigated. 13C chemical shifts of carbon atoms in the copolymers and in addition in model molecules of the two modes of styrene addition indicate that styrene insertion into carbon-metal bonds of the catalyst proceeds according to a primary mode. Mechanistic implications of these results are discussed.0025-1 16)3/87/$03.00 K Results and discussion Synthesis of styrene/]-hexene copolymersStyreneA-hexene copolymers of various chemical composition were prepared in toluene and heptane at 45 "C with the isospecific Tic& (a)-AlEt, (I : 3) catalyst25). Percentages of styrene and I -hexene monomeric units in the copolymers, determined by H NMR, are given in Tab. 1. In order to obtain a comparison with previous data reported by Anderson (a-Tic&-AlEt, (1 : 3), r, = 10, rs = 0,2)z6) an apparent monomer reactivity ratio was calculated using the Fineman-Ross method (r, = 9,8; r, = 0,6). The data are in good agreement. The significance of the reactivity ratios will be examined in more detail in a following section. Gel permeation analysis of the copolymers