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

Qiong Wu,Rosario Benavente,Rosa Barranco-García,José Manuel Gómez-Elvira,Alberto García-Peñas,Ernesto Pérez,María Luisa Cerrada

doi:10.3390/polym11081266

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.

Highlights

Incorporation of small quantities of a comonomer, mostly an α-olefin, into ethylene or propene polymerizations usually enhances the kinetics of the process
The phenomenon has been reported in Ziegler-Natta, Phillips, and metallocene catalysts with a large variety of comonomers [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34] and great concern exists in explaining its true nature, since it has important consequences from a production point of view [16]
Assignments were made according to literature [60,61] and they are shown in Figure 1 for the particular case of samples obtained at 60 ◦ C. They were identified in the figure using the established nomenclature branched polyolefin copolymers [62]

Summary

Introduction

Incorporation of small quantities of a comonomer, mostly an α-olefin, into ethylene or propene polymerizations usually enhances the kinetics of the process. This is what is known as the comonomer effect. The phenomenon has been reported in Ziegler-Natta, Phillips, and metallocene catalysts with a large variety of comonomers [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34] and great concern exists in explaining its true nature, since it has important consequences from a production point of view [16].

Methods

Results

Discussion

Conclusion