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

Abstract

An operationally simple approach to preparation of ωnorbornenyl macromonomers (MMs) is reported. Reaction of exo-N-(6hydroxyhexyl)-5-norbornene-2,3-dicarboximide or exo-N-(10-hydroxydecyl)-5-norbornene-2,3-dicarboximide with α-phenyl acrylate (α-PhA) led to novel end-capping agents, NBxPhA [x is 6 (n-hexyl) or 10 (ndecyl)]. Living anionic polymerization of styrene and methyl methacrylate followed by capping with NBxPhA yielded the desired MMs, ω-norbornenyl polystyrene (NBxPS) and ω-norbornenyl poly-(methyl methacrylate) (NBxPMMA). These MMs, formed with controlled molecular weights (M n = 2−5 kDa) and low dispersity (Đ = 1.02−1.07), upon ring-opening metathesis polymerization (ROMP) resulted in P(NB-g-PS) and P(NB-g-PMMA) bottlebrush homopolymers with ∼95% and ∼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 (Đ = 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, Đ = 1.09−1.32) displaying photonic crystal properties.

Cationic Bottlebrush Polymers from Quaternary Ammonium Macromonomers by Grafting‐Through Ring‐Opening Metathesis Polymerization

“…To confirm this behavior, the bottlebrush polymers made at different MM:G3 and after 53 min of polymerization were examined via SEC where the chromatograms (Figure 2c) showed unimodal curves of each bottlebrush polymer. A long tail at low molecular weight was observed in the polymerization of MM:G3 of 100, which may be from intramolecular chain transfer reactions or some termination during ROMP 71,81. As expected for controlled ROMP of PDMAEA‐C6‐Br 14, the M n was linearly related to the initial MM:G3 (Figure 2d).…”

“…A low loading of AIBN at 52 °C was used to avoid generating a high number of active radical chains, which subsequently suppressed chain end coupling or termination side reactions to generate MMs with one norbornene group (NB) per chain. Also, low percent conversions (35–45%) were targeted to avoid the polymerization of the norbornene groups 69–71 . 1 H‐NMR spectra confirmed that no undesired reactions took place during RAFT polymerization as indicated by good agreement of relative integration ratios of the norbornene olefin peaks and the peaks associated with the RAFT chain transfer agent at the other end of the chain (Figures S2 and S3, Supporting Information).…”

“…The molecular weight of MMs can also influence bottlebrush polymer synthesis via ROMP due to steric hindrance at the ruthenium active site on the propagating chains slowing monomer addition 71,84. To explore the range of suitable quaternary ammonium MM molecular weights for well‐defined bottlebrush polymerization, larger quaternary ammonium MMs (NB‐PDMAEA‐C6‐Br 19 and NB‐PDMAEA‐C6‐I 19 were prepared and polymerized under the same conditions as lower molecular weight MMs ([MM] 0 = 0.03 m and MM:G3 = 50:1, Table 2, entry 7).…”

“…Larger MMs significantly slowed ROMP yielding a k app of 0.014 min −1 ( Figure a and Figure S30, Supporting Information) and about 30% conversion at 1 min as compared to 48% conversion for the shorter MM chain. Steric crowding from the longer side chains surrounding the ruthenium active center likely was the cause 42,71,84. However, larger MMs also increased the [Br‐] 0 , which could have impacted the ROMP propagation rate as well.…”

“…Since the controlled polymerization of NB‐DMAEA‐C6‐Br 14 to varied DPs was demonstrated, amphiphilic bottlebrush block copolymerization was examined by utilizing NB‐PDMAEA‐C6‐Br 14 and a polystyrene MM, NB‐PS 17 . NB‐PS MMs have been widely polymerized by ROMP to yield well‐defined bottlebrush block copolymers using a variety of anchor norbornene groups 41,71,76. In this work, a NB‐PS MM with the same anchor group as the quaternary ammonium MMs was prepared from RAFT polymerization to obtain a 17 DP MM (2000 g mol −1 ).…”