Telechelic polycyclooctenes (PCOEs) have been successfully synthesized by ring-opening metathesis polymerization (ROMP)/cross-metathesis (CM) of cyclooctene (COE) using Grubbs’ second-generation catalyst (G2) in the presence of epoxide-functionalized chain-transfer agents (CTAs). The monofunctional epoxide oxiran-2-ylmethyl acrylate CTA (1) afforded the isomerized α-(glycidyl alkenoate),ω-propenyl functional (IMF) PCOEs. The use of 1,4-benzoquinone (BZQ) as additive completely inhibited the C═C isomerization process, thereby leading selectively to α-(glycidyl alkenoate),ω-vinyl telechelic (MF) PCOE. On the other hand, difunctional epoxide CTAs, bis(oxiran-2-ylmethyl) fumarate (3), bis(oxiran-2-ylmethyl) maleate (4), bis(oxiran-2-ylmethyl) (E)-hex-3-enedioate (5), and (Z)-1,4-bis(oxiran-2-ylmethoxy)but-2-ene (6), selectively afforded the corresponding α,ω-di(glycidyl alkenoate) telechelic PCOEs (DF) along with minor amounts of cyclic nonfunctional (CNF) PCOE. In the presence of these difunctional symmetric...