Determination and Application of the Cohesive Energy Density of Amorphous Polyethylene at Room Temperature
The cohesion energy density describes the magnitude of intermolecular forces,which is one of the most fundamental concepts in polymer physics.The physical properties of polymers are closely related to the cohesion energy density.In undergraduate polymer physics teaching,polyethylene,due to its high crystallinity,was often described as the only exceptional case of the rule that"the density of cohesion energy is used to determine the macroscopic use of the material".It is highly desired to prepare completely amorphous polyethylene at room temperature.In this paper,an α-diimine nickel catalyst(NiB)was used to catalyze the pressurized polymerization of ethylene to successfully synthesize amorphous polyethylene(Mw:2.01×105 g/mol,PDI:1.80,Branches:107/1000C,Tg:-63.1 ℃,p:0.856 g/cm3)at room temperature.The maximum characteristic viscosity method was used to measure the cohesive energy density of polyethylene as 259 J/cm3,which was very close to the value estimated by the group contribution method.The amorphous polyethylene exhibited a rubbery macroscopic behavior at room temperature.As a result,the correlation between the measured cohesion energy density(＜300 J/cm3)and the rubbery macroscopic behavior is not exceptional but follow the general rule.
Polymer physicsCohesion energy densityAmorphous polyethylene
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