A study on the effect of polyhedral oligomeric silsesquioxane (POSS) on the mechanical properties of polyethylene using molecular dynamics simulations

The influence of polyhedral oligomeric silsesquioxane (POSS) as a pendant group on polyethylene backbones was studied with atomistic molecular dynamics simulations. Neat polyethylene and three copolymers with various ratios of POSS units were modeled, and the volume-temperature curves were obtained. From the break of the slope of the curves, the glass transition temperatures were obtained. Meanwhile, the elastic moduli of the polymers were calculated from the stress and strain fluctuation formula. The results show that the glass transition temperatures of the four polymers are almost the same. However, the elastic modulus first decreases and then increases to the maximum, afterwards descending with the increasing ratio of the POSS content. Based on the analysis of the variation of every part of the potential energy, it was concluded that the torsion of the main chain and the relative movement between the chains contribute to the glass transition. On the other hand, the van der Waals interactions between the POSS unit and the main chains play an important role in the enhancement of the elastic modulus.