Facile Access to gem-Trifluoromethyl/Boron-Functionalized Polymers via Free-Radical Copolymerization and Cotelomerization

Abstract

Functional fluoropolymers are important for various applications due to the integrated characteristics of functional groups and fluorocarbon segments. Herein, we developed (1) thermally initiated and visible-light-initiated copolymerization of (trifluoromethyl)­vinyl boronic esters (CF3VBs) and unconjugated alkenes (18 examples, including vinyl ethers, esters, and amides), enabling the efficient synthesis of a broad scope of fluoropolymers in 71–92% yield and variable fractions of gem-CF3/B substituents (F CF3VB = 0.26–0.84) at different molar masses (M n = 5.2–33.4 kDa) and (2) visible-light-initiated cotelomerization of CF3VB and unconjugated alkenes with p-tolyl disulfide as a telogen (M n = 3.6–13.0 kDa). Reactivity ratios for copolymerization were determined by the Meyer–Lowry method at 65 °C (for BVE: r CF3VB = 1.254, r BVE = 0.006; for VAc: r CF3VB = 0.235, r VAc = 0.042; for NVP: r CF3VB = 1.067, r NVP = 0.063). The achieved high fractions of CF3VBs in copolymers are also confirmed by density functional theory (DFT) calculation results. Through post-polymerization modifications, gem-CF3/B units could transform into various copolymers and terpolymers with geminal functionalities (e.g., gem-CF3/OH, gem-CF3/vinyl, gem-CF3/furan). The increase of geminal functionalities enables clearly amplified chemical responsiveness toward pH variation, as demonstrated by fluoropolymers with gem-CF3/OH.

Electron-Poor Butenolides: The Missing Link between Acrylates and Maleic Anhydride in Radical Polymerization

“…The agreement of these observations with our DFT thermochemistry calculations is remarkable. We calculated the energy barrier for the addition of MVE- or NVP-based radicals to their parent monomers or to butenolides ( 1a or 2a ) and repeated the operation for the subsequent addition of the resulting radicals (Figure at the MN15/def2tzvpp/SMD=THF level of theory) . In nearly all cases, homoaddition is disfavored by 1.8–7.8 kcal/mol compared to heteroaddition, altogether supporting an alternating copolymerization mechanism.…”

“…The differences observed in the rate of copolymerization seem to correlate to the electron-withdrawing character of the acetal substituent, and we performed DFT calculations to support these observations (at the MN15/def2tzvpp/SMD=THF level of theory) . Considering an alternating radical copolymerization mechanism, , we were happy to find that the addition of the methyl vinyl ether (MVE) radical to a butenolide has a lower activation barrier with acetyl and benzoyl substituents than with a methoxy group and that there is a higher gain in energy as well (Figure ).…”

Characterization of Styrene–Vinyl Alcohol Copolymers by CP-MAS NMR Spectroscopy

“…25 Very recently, Chen et al reported free-radical polymerization of gem-trifluoromethyl/boron-functionalized monomers. 26 An advantage of organoborane monomers is a closer match in reactivity ratios with St that allows for higher incorporation of hydroxyl side chain precursors in copolymers. For example, we have reported styrenic copolymers with 50, 75%, and as high as 90% incorporation of BN2VN.…”

“…BN2VN’s aromaticity results in a close agreement in reactivity ratios with styrene (St) during radical polymerization ( r 1 (St) = 2.30; r 2 (BN2VN) = 0.423) and compatibility with coordination polymerization catalysts. , Organoborane oxidation under aqueous or organic conditions afforded vinyl alcohol (VA) (co)­polymers. , Ouchi and Nishikawa have described isopropenyl pinacol boronate ester (IPBpin) as an electron-rich monomer that copolymerizes with St ( r 1 (St) = 1.41; r 2 (IPBpin) = 0.085) and can be oxidatively converted to methyl vinyl alcohol residues. , In 2021, Ouchi and Nishikawa reported vinyl pinacol boronate ester (VBpin)–styrene copolymerizations ( r 1 (St) = 3.77; r 2 (VBpin) = 0.25) and postpolymerization organoborane oxidation . Very recently, Chen et al reported free-radical polymerization of gem-trifluoromethyl/boron-functionalized monomers …”

Orthogonal C–B Bond Transformation as an Approach for Versatile Synthesis of End-Functionalized Polymers

“…Considering the wide range of transformability of the boronyl group, this strategy would contribute to the versatile synthesis of end-functionalized polymers. Recently, PPM using a carbon–boron bond as the reaction site has attracted attention, and indeed many papers have been reported by some groups other than ours . The orthogonal transformation approach would open the door to syntheses of other types of inaccessible end-functionalized polymers.…”