Thermal studies on ethylene–vinylcyclohexane copolymers prepared with bis-indenyl type metallocene catalyst systems

Abstract

Ethylene–vinylcyclohexane copolymers (EVCH) were synthesized with unsubstituted and substituted bis-indenyl type metallocene catalysts and their thermal and dynamic mechanical behavior was studied and compared to a series of metallocene catalyzed ethylene-1-hexene (EH) and ethylene-1-hexadecene (EHD) copolymers. Increasing comonomer incorporation in the chain decreased the melting point, the level of crystallinity, and the density of all copolymers, but the bulky size of the vinylcyclohexane (VCH) group made this decrease very insignificant for the EVCH copolymers. The influence of the VCH group was also noticed in the loss tangent curves by dynamic mechanical analysis as a very insignificant shift of the β-transition to lower temperatures at increasing comonomer content, a behavior quite opposite to the behavior of the EH and EHD copolymers. The storage modulus curves explained that the stiffness properties of the EVCH copolymers are as good or better than those of the EH and EHD copolymers at the same comonomer level. The intensities of the maximum in the loss tangent curves indicate that EVCH copolymers may have good impact properties. Fractionation studies by differential scanning calorimetry (DSC) using a self-nucleation/annealing (SSA) procedure confirmed a broadening of the lamellar thickness distribution as the amount of comonomer increased. Self-nucleation/annealing curves of highly branched EVCH and EH copolymers exhibited big similarities suggesting similar random comonomer distributions.