MD Simulation Study of the Influence of Branch Content on Relaxation and Crystallization of Branched Polyethylene Chains with Uniform Branch Distribution

Linear low-density polyethylene (LLDPE) chains with different levels of branch content (BC), ranging from 10 to 80 branches/1000 C, distributed uniformly along the chain are simulated in vacuum at a temperature of 350K. The influence of BC on the relaxation and crystallization of LLDPE chains is studied. The collapse of the branched chains is found to occur via a local followed by a global collapse mechanism with branches acting as nucleation points for the collapse of the molecule leading to faster collapse of chains with higher BC. Branches are observed to selfassemble away from the backbone at high BC. Radius of gyration correlates to Mw by a power-law relationship: Rg=Ks α w M with α=0.35. The trans population is found to be dominant at all branch contents; however, it decreases with increasing BC. Increasing BC is found to decrease order and to strongly influence chain conformation. Chain conformation undergoes a transition from lamellar to a more random coil-like structure near a critical BC of 50 branches/1000 C. Branches are observed to be excluded from the lamella and to self assemble at high BC. This work also provides insight into the conformation adopted during the coil-globule transition experienced by a single chain in an infinitely dilute solution much below the θ temperature.