Two series of polyolefin-based bottlebrush polymers were synthesized using ring-opening metathesis polymerization of norbornenyl-functionalized macromonomers to compare the rheology of systems with and without the presence of side chain entanglement. The first series of bottlebrushes includes atactic polypropylene (aPP) branches with a fixed length of Mbranch = 2.05 kg/mol and variable backbone degree of polymerization ranging from 11 to 732 (Mw = 22–1500 kg/mol). The branches in this series are shorter than the entanglement molecular weight of aPP (Mbranch/Me ≈ 0.5). The second series utilizes poly(ethylene-alt-propylene) (PEP) branches with Mbranch = 6.7 kg/mol and variable backbone degree of polymerization ranging from 13 to 627 (Mw = 89–4200 kg/mol). The branches in this series exceed the entanglement molecular weight of PEP (Mbranch/Me ≈ 3.5). The linear viscoelastic responses of each sample were examined using small-amplitude oscillatory shear measurements, and dynamic master curves were constructed...