Polyethylene flow activation energies

Molecular Weights, Flow Activation Energies and Type of Catalyst for a Series of Polyethylenes Examined for Long Chain Branching. 

Nakajima, N., G. A. Tirpak, and M. Shida Branching and flow activation energy of conventional high pressure process polyethylene. J. Pol5rmer ScL 3B. 1089 (1965). 

Interestingly, for the polymers produced with 1/MAO, 3/MAO, and 6/MAO, a clear deviation from linearity is seen only at the lowest Ce- At high ethylene concentration, the difference between expected t]o and measured t] a> = 0.02 rad s ) values became smaller and the flow activation energy values of these polymers were comparable to the values expected for linear polyethylenes [46, 51]. 

As shown in Table 4, introduction of 1-hexadecene as comonomer has a similar influence to hydrogen on the rheological properties of the polyethylene the tj o = 0.02 rad s ) and G values were lowered, indicating suppression of the LCB. The flow activation energy value, a remained almost unchanged due to two opposite effects at play simultaneously. For flow E, two different effects of the comonomer incorporation are present an increase in the comonomer content in a linear polymer will increase E, but for the LCB, a decrease in the LCB content would decrease the E value. 

Three assumptions have been made to estimate the molecular length required to achieve main chain scission (a) the simultaneous and concerted motion of the monomer units (b) the equal interaction energy between the corresponding monomer units in adjacent polymer chains (c) the flow activation energy for the corresponding monomer is an approximation for E. In the case of polyethylene, E is 1.01 kcal/mole and the bond energy is about 82 kcal/mole. 

We have also carried out some unpublished studies on the temperature dependence of hydrophobic recovery of plasma treated PDMS. The activation energy of this thermal restructuring process is 44 kJ/mol. This is more than the activation energy of viscous flow of PDMS (15 kJ/mol) 2 but much less than the only similar measurement of which we are aware for a carboxylic acid functionalized polyethylene surface (210 kJ/mol). ... 

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