A New Insight into the Comonomer Effect through NMR Analysis in Metallocene Catalysed Propene–co–1-Nonene Copolymers

Abstract

The “comonomer effect” is an intriguing kinetic phenomenon in olefin copolymerization that still remains without a detailed explanation. It typically relates to the rate of enhancement undergone in ethylene and propene catalytic polymerization just by adding small fractions of an alpha-olefin. The difficulty lies in the fact that changes caused by the presence of the comonomer in reaction parameters are so conspicuous that it is really difficult to pin down which of them is the primary cause and which ones are side factors with marginal contribution to the phenomenon. Recent investigations point to the modification of the catalyst active sites as the main driving factor. In this work, the comonomer effect in the metallocene copolymerization of propene and 1-nonene is analysed and correlated to the comonomer role in the termination of the chain-growing process. The associated termination mechanisms involved furnish most of chain-free active sites, in which the selective interaction of the comonomer was proposed to trigger the insertion of monomers. A thorough characterisation of chain-end groups by means of the 1H NMR technique allows for detailing of specific transfer processes, ascribed to comonomer insertions, as well as evidencing the influence of the growing chain’s microstructure over the different termination processes available.

Microstructural details and polymorphs in poly(propylene‐ co ‐1‐nonene) copolymers synthesized at different polymerization temperatures

“…The presence of regiodefects is also observed, which are mainly associated with the homopolymer and copolymers with low comonomer content. [57] Comonomer distribution at the triad level as well as the average propylene length (n p ) are listed in Table 4 and have been also are also exhibited in other copolymers. In general, presence of diads is reported for comonomer compositions higher than 5 mol%, and they coexist with isolated units that are disrupting the polypropylene segments.…”

“…On the other hand, mmmr sequences are enlarged as comonomer content rises and also, significantly, as polymerization temperature increases. The growth in mmmr sequences could be explained from the temperature effect on frequency of error insertions, [ 57 ] as can be seen from the 13 C NMR peaks. Nevertheless, the appearance of other tacticity sequences could be associated with other effects.…”

“…The presence of regiodefects is also observed, which are mainly associated with the homopolymer and copolymers with low comonomer content. [ 57 ]…”

Integrated Effect of Comonomer and Catalyst on Copolymerization of Ethylene with Allylcyclopentane or Allylcyclohexane by Using Metallocene Catalysts

“…Comonomer effect is an important aspect in the study of coordination polymerization of olefin, and usually refers to the influence of the introduction of comonomer on the polymerization activity. [17][18][19][20][21] Although comonomers have a very significant effect on polymers, there are few reports on the study of polymer composition, structure and properties from the point of view of polymerization. [22,23] Previously, we studied the comonomer effects for olefin copolymerization by using metallocene and half-metallocene catalyst systems.…”

“…The polymerization behavior of catalyst is influenced by the introduction of comonomer. Comonomer effect is an important aspect in the study of coordination polymerization of olefin, and usually refers to the influence of the introduction of comonomer on the polymerization activity . Although comonomers have a very significant effect on polymers, there are few reports on the study of polymer composition, structure and properties from the point of view of polymerization .…”