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Controlled Ring-Opening Metathesis Polymerization of a Monomer Containing Terminal Alkyne and Its Versatile Postpolymerization Functionalization via Click Reaction Kyung Oh Kim, Jonglak Kim, and Tae-Lim Choi* Department of Chemistry, Seoul National University, Seoul 151-747, Korea S Supporting Information *
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the endo-tricyclo[4.2.2.02,5]deca-3,9-diene (TD)7 unit proceeded with much faster initiation than did ROMP of conventional norbornene monomers.7d,e This is because the reactivity of cyclobutene on TD-derived monomers is much higher than that with norbornene analogues, resulting in faster coordination of TD-derived monomers to the catalyst and thereby increasing the ki/kp ratio. Furthermore, living polymerization of the TD-derived monomers became possible even with the slow-initiating (but thermally stable) secondgeneration Hoveyda−Grubbs catalyst.7e This result led us to propose the use of TD monomers might improve the catalyst preference for the alkene (cyclobutene) over the alkyne, thereby allowing for the direct ROMP of monomers containing the unprotected terminal alkyne moiety. Herein, we engineer the monomer structure to include the more reactive cyclobutene group of the TD unit tethered to an alkyne, which is less reactive owing to steric protection offered by the dimethyl substituents at an adjacent site (Scheme 1). We show for the first time that this monomer successfully undergoes ROMP in a controlled manner. The resulting polymer had a high molecular weight (21 kDa) and narrow Đ (99 >99 >99 81 71 53
[M]/[I] = 100. bThe polymerization was terminated intentionally at certain conversion. cMn and Đ were calculated by THF SEC using PS standards. dConversion was calculated from ratio of the remaining alkene to internal standard by 1H NMR.
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dx.doi.org/10.1021/ma500877n | Macromolecules XXXX, XXX, XXX−XXX
Macromolecules
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Figure 2. (a) SEC traces and (b) plot of reaction time vs −ln([M]/[M]0) of poly(2).
Table 2. Postpolymerization Functionalization to Poly(2) via Cu-Catalyzed Azide−Alkyne Cycloadditiona
a Prepolymer with Mn = 14K and Đ = 1.09 was used. bMn and Đ were calculated by THF SEC using PS standards. cConversion was calculated by 1H NMR. dIsolated yield after precipitation in MeOH. e3 equiv of azide was used for CuAAC, and the reaction time was 1 day.
that the controlled ROMP of the alkyne-containing monomer was achieved without any defects, owing to proper application of a monomer containing an activated olefin within the TD subunit and a sterically protected alkyne. With polymer samples in hand, we shifted our focus to the postpolymerization functionalization of poly(2) by employing the click reaction. In an initial trial, poly(2), 3 equiv of n-heptyl azide, and a catalytic quantity of CuBr(PPh3)3 were heated to 50 °C in DMF for 20 h. Unfortunately, the reaction was not complete after this time (Table 2, trial 1), and it appeared that a more reactive catalytic system was required for this postpolymerization functionalization because the sterically hindered alkyne moiety was resistant to the CuBr(PPh3)3-
peak in SEC trace completely disappeared, with up to 81% conversion (DP = 81) of monomer 2 (Figure 2a). To further support this proposal, polymerization of 2, with [M]/[I] ratios of 50 and 70, was conducted, resulting in full conversion. The resulting polymer samples again showed small shoulder peaks in the SEC traces in each case, whereas in the cases where polymerization was terminated early, clear monomodal traces with narrower Đ (
