One new and one established functional cyclooctene were prepared and (co)polymerized using ring-opening metathesis polymerization. The resulting polymers were hydrogenated to yield the corresponding functional polyolefins that were structurally equivalent to copolymers of ethylene and either methyl methacrylate, t-butyl acrylate, or acrylic acid after deprotection. The copolymers that incorporate methyl methacrylate into the backbone were used as compatibilizers for poly(methyl methacrylate)/polyethylene blends. The copolymers that incorporate t-butyl acrylate into the backbone yielded elastomers that could be thermally crosslinked. V C 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3117-3126 KEYWORDS: compatibilization; copolymer; methyl methacrylate; ROMP; thermoset polyolefins INTRODUCTION The ring-opening metathesis polymerization (ROMP) of functionalized cyclooctenes (COEs) followed by hydrogenation of the olefinic groups in the polymer backbone is a powerful method for the preparation of functionalized polyolefins. Many 3-substituted COEs provide regiospecific polymers 1 while 4-and 5-substituted COEs typically give regioirregular polymers. The broad utility of this approach to materials useful for a wide variety of interesting applications has been clearly demonstrated in the literature. [2][3][4] The success of these approaches can be in large part attributed to the robust nature of ruthenium-based metathesis catalysts developed by Robert H. Grubbs and coworkers. [5][6][7] Indeed, these catalysts have been referred to by some as empyrean. 8