Poly(Ethene-co-Norbornene) Obtained with a Constrained Geometry Catalyst. A Study of Reaction Kinetics and Copolymer Properties

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 one hour
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 both by 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 based on the proposed reaction scheme.