A study of the synthesis and characterization of ethylene/dicyclopentadiene copolymers using a metallocene catalyst

Copolymers of ethylene/dicyclopentadiene were produced using a Me2Si(Ind)2ZrCl2/methylaluminoxane catalyst system. The melting and crystallization points of the freshly prepared copolymers steadily decreased with increasing comonomer concentration. This was attributed to increased comonomer concentration in the polymer. When the comonomer incorporation, as measured by 13C NMR, is plotted against the comonomer concentration in the reactor, a plateau appears at concentrations higher than 0.12 mol/L. At concentrations greater than 0.12 mol/L time dependant crosslinking begins to be observed in the copolymers after exposure to air for several months. This crosslinking is also apparent in the thermosetting behavior of the copolymers when they are allowed sufficient time to crosslink. Copolymers with lower comonomer concentrations possess melting enthalpies even after several weeks, suggesting that there is a threshold concentration of 0.12 mol/L for the crosslinking process. Tensile tests of thermoplastic samples showed that incorporation of ca. 5 mol% of comonomer into the polyethylene main chain results in a semi-elastomeric material which possesses high strain recovery and whose strain hardening is similar to that observed for the homopolymer.