Impact of short chain branching on conformations of metallocene LLDPE melts: NMR, light scattering and MD simulation study

The influence of short chain branching on molecular conformations of melts and solutions of metallocene linear Low-density polyethylene (m-LLDPE) was studied by nuclear magnetic resonance (NMR) spectroscopy, light scattering, and Molecular Dynamics (MD) simulation techniques. Both T-2 relaxation measurements by NMR and MD simulations suggest the loss of molecular order in m-LLDPE at temperatures >135 degrees C. Similar trends were observed for the radius of gyration as measured by light scattering and calculated from MD simulations vs. branch content (BC) and type. At high BC (>40 branches/1000 C) m-LLDPE tends towards self assembly. Neither the branch type nor the BC has significant effect on the intermolecular orientation correlation function. This might be attributed to the fact that the high temperature of the melt results in loss of order in the chains. This lack of order is independent of BC or type. This result is in agreement with the results of the dihedral distribution analysis. Also, it is in agreement with our NMR T-2 measurements. The radial distribution functions are nearly identical indicating no effect of branch type at low branch density on the correlation between branches and backbone segments. However, increasing the BC to 80 branches/1000 C resulted in a change in the correlation between the branches and backbone segments.