Cyclobutenes containing pendant groups of varying sizes were polymerized via ring opening metathesis polymerization using Grubbs catalyst 2nd generation (G2). The rate of polymerization depended on the size of the pendant groups attached to the cyclobutene rings, with longer side-chains producing slower polymerization rates and narrower molecular weight distributions. The polymerization of these new molecules proceeded with first order kinetics, consistent with a living polymerization. Chain extension experiments produced cyclobutene-based diblock copolymers with polydispersity indices below 1.33. The synthetic methods in this report will allow the use of G2 to access new complex polymeric architectures with a higher density of pendant groups than those derived from norbornene analogs and cyclooctene moieties. (c) 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 1929-1939