ω-Norbornenyl Macromonomers: In Situ Synthesis by End-Capping of Living Anionic Polymers Using a Norbornenyl-Functionalized α-Phenyl Acrylate and Their Ring-Opening Metathesis Polymerization

An operationally simple approach to preparation of omega-norbornenyl macromonomers (MMs) is reported. Reaction of exo-N-(6-hydroxyhexyl)-5-norbornene-2,3-dicarboximide or exo-N-(10-hydroxydecyl)-5-norbornene-2,3-dicarboximide with alpha-phenyl acrylate (alpha-PhA) led to novel end-capping agents, NBxPhA [x is 6 (n-hexyl) or 10 (n-decyl)]. Living anionic polymerization of styrene and methyl methacrylate followed by capping with NBxPhA yielded the desired MMs, omega-norbornenyl polystyrene (NBxPS) and omega-norbornenyl poly-(methyl methacrylate) (NBxPMMA). These MMs, formed with controlled molecular weights (M-n = 2-5 kDa) and low dispersity ((D) over bar = 1.02-1.07), upon ring-opening metathesis polymerization (ROMP) resulted in P(NB-g-PS) and P(NB-g-PMMA) bottlebrush homopolymers with similar to 95% and similar to 75% yield, respectively, signifying efficient end-capping efficiency. The factors affecting synthesis of NBxPS and NBxPMMA and their subsequent ROMP, such as [NBxPhA]/[sec-BuLi] ratio, the length of alkyl spacer, and varying molecular weights of the macromonomers, were optimized. Well-defined bottlebrush homopolymers with low polydispersity ((D) over bar = 1.02-1.39) were achieved at various degrees of polymerization (DP 50-600). Additionally, copolymerization of the homopolymers through sequential ROMP furnished the bottlebrush block copolymers (M-n = 262-1593 kDa, (D) over bar = 1.09-1.32) displaying photonic crystal properties.