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

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.This research was funded by the Agencia Estatal de Investigacion (AEI, Spain), together with the European Regional Development Fund (FEDER, UE), grant number MAT2016-79869-C2-1-P. Human resources funding was provided by the Hong Kong University of Science and Technology, in the frame of the CSIC-HKUST cooperation, grant number HKUST2017-25, and by the Ministerio de Economía y Competitividad (MINECO, Spain), grant number BES-2014-07097