Thermodynamics and rheology of cycloolefin copolymers

Cycloolefin copolymers of ethylene and norbornene, with norbornene content in the range from $36to62mol%$⁠, were studied with respect to the thermal, thermodynamic, and rheological properties using differential scanning calorimetry, pressure-volume-temperature, and dynamic mechanical measurements. All copolymers obey the principle of time-temperature superposition, i.e., they can be considered as thermorheologically simple except for a temperature range in the vicinity of $Tg$⁠. Despite this, the results on (i) the ratio of activation energies $EV*∕H*$ used to quantify the origin of the liquid-to-glass transition, (ii) the pressure coefficient of the glass temperature $Tg(P)$⁠, and (iii) the dynamic fragility $m$ suggest increasing dynamic heterogeneity with increasing norbornene content that is driven by the structural heterogeneity along the backbone.