Study of the crystallization behavior of model polyolefins under quiescent and flow conditions using hyphenated techniques of rheology, NMR, and X-ray scattering
Experimental and Theoretical Physics of Polymers
Polymer Materials
Final Report Abstract
Model polyolefins with a narrow molecular weight ranging from 10 kDa to 5300 kDA with a narrow polydispersity and a low side chain content were synthesized using a MAO activated early transition metal catalyst. The polymerizations were performed in either a metal reactor or a custom-made glass apparatus. The pre-catalyst requires activation by an aluminum alkyl, and synthesis of polyethylene’s without residues arising from the co-catalyst required a modification of the polymerization procedure. All of the received 13 model mono-dispersed PEs from the cooperation partner, University of Konstanz, were firstly checked about the purity. Three of them contained substantial Al2O3 impurities, and the PE11 (Mw = 11 kg/mol) exhibits fast crystallization thus challenging for rheological measurement. Therefore, the 9 left model PEs were adapted together with one commercial grade PE for Rheo-NMR studies. The experimental protocol of Rheo-NMR on PE has been established for the first time, including the specific temperature calibration, rheometer setting, NMR setting as well as data-batch process. According to the correlation results, the complex viscosity |η∗| of the materials increases as a function of the volume fraction of crystals, ϕc. However, the |η∗|(ϕc) of the monodispersed model PEs maintains an extended Einstein behavior while the poly-dispersed PEs and i-PP only exhibit a sigmoidal growth. We thus submit that molecular weight distribution is a major parameter for controlling the PE crystallization process – our findings have thus key potential implications for different industrial applications.
