Poly(ethene-<i>c</i><i>o</i>-norbornene) Obtained with a Constrained Geometry Catalyst. A Study of Reaction Kinetics and Copolymer Properties

Abstract

Poly(ethene-co-norbornene) was synthesized in toluene using Me2Si(Me4Cp)(NtBu)TiCl2 activated with methylaluminoxane (MAO) as catalyst. We found that at 50 °C the molecular weight increases with time for up to 1 h, and very little chain transfer occurs; thus, the copolymerization can be considered as quasi-living. The quasi-living nature requires high norbornene feed fractions; it is more pronounced at low temperatures and short reaction times. Mw/Mn = 1.3 (Mn = 100 kg/mol) was the lowest polydispersity index obtained when the copolymerization reaction was conducted at 50 °C. Poly(ethene-co-norbornene) containing long chain branches was obtained; the degree of branching decreased with an increasing norbornene molar fraction in the feed. The presence of long chain branches was confirmed by both size exclusion chromatography and rheology; the branches were found evenly distributed in the copolymers. Rheology of poly(ethene-co-norbornene) was analyzed; the GN° minimum could be reached, most probably, because bulky bicyclic norbornene units inhibit crystallization. Compared to the literature data, the low level of long chain branches incorporated into our poly(ethene-co-norbornene) samples does not significantly affect the glass transition temperature. The relationship between the experimental conditions and the polymer architecture is discussed on the basis of the proposed reaction scheme.