The role of monomer geometry on the properties of polyolefins: A numerical study

We explore the role of monomer geometry on the structural, dynamic, and thermodynamic properties of polyolefis by employing all-atom molecular dynamic simulations. Specifically, we compare properties of atactic polyolefins in the molten state including polypropylene (aPP), a short-chain branched polymer: poy(1-hexene) (aPH), and a polymer having cyclic olefins: poly(vinyl cyclobutane) (aPVCB). We find polymers having the same chain mass and atom composition (hydrocarbon-based molecules), but having different monomer architecture differ strongly in material properties. In particular, the polymer glass transition ( $T_{\mathrm{g}}$) and bulk modulus ( $B$) show higher values for aPVCB in comparison to aPP and aPH. This increase is caused by having the carbon atoms in a cyclic structure, making aPVCB achieve higher mass and energy densities. By contrast, adding linear short side chains to polymer backbones causes a reduction in $T_{\mathrm{g}}$ and $B$, since side chains make backbones displace each other reducing their packing and thus their mass and energy densities. More broadly, our numerical results suggest that the incorporation of VCB monomers to linear polyolefins will enhance their properties, opening the possibility for designing a new set of materials.