Propene-norbornene copolymers by C2-symmetric metallocene rac-Et(Ind)2ZrCl2:: Influence of reaction conditions on reactivity and copolymer properties

The copolymerization of propene and norbornene by catalytic systems composed by C-2 symmetric rac-Et(lnd)(2)ZrCl2 (1), methylaluminoxane, and triisobutylaluminum was investigated. Propene-norbornene (P-N) copolymers with about 50 mol % of norbornene are highly alternating at low temperature and pressure. The influence of propene pressure (1-8 bar) and temperature (30-70 degrees C) on activity, norbornene content, molar inasses, and glass transition temperatures of (P-N) copolymers has been assessed. A deeper analysis of the complex C-13 NMR spectra of these copolymers has allowed us to evaluate the diad composition, as well as the propene placement in the chain. A great number of 1,3-propene insertions were found, all occurring after an inserted norbornene unit, especially at high temperature and pressure. This indicates that the limiting step in P-N copolymerization is the difficulty to insert a P after N. For the first time, copolymerization parameters were estimated. It was found that P-N copolymers are alternating at temperature as low as 30-40 degrees C and tend to become random as temperature increases. Chain terminations are likely to occur when the last inserted unit is propene. This along with an increase in k(P) would explain the decrease of norbornene content, molar mass, and glass transition temperature, observed at high T and P.