Para-Fluoro Postpolymerization Chemistry of Poly(pentafluorobenzyl methacrylate): Modification with Amines, Thiols, and Carbonylthiolates

A methacrylic polymer undergoing highly efficient para-fluoro substitution reactions is presented. A series of well-defined poly(2,3,4,5,6-pentafluorobenzyl methacrylate) (pPFBMA) homopolymers with degrees of polymerization from 28 to 132 and Đ ≤ 1.29 was prepared by the RAFT process. pPFBMA samples were atactic (with triad tacticity apparent in 1H and 19F NMR spectra) and soluble in most organic solvents. pPFBMA reacted quantitatively through para-fluoro substitution with a range of thiols (typically 1.1 equiv of thiol, base, RT, <1 h) in the absence of any observed side reactions. Para-fluoro substitution with different (thio)carbonylthio reagents was possible and allowed for subsequent one-pot cleavage of dithioester pendent groups with concurrent thia-Michael side group modification. Reactions with aliphatic amines (typically 2.5 equiv of amine, 50–60 °C, overnight) resulted in complete substitution of the para-fluorides without any observed ester cleavage reactions. However, for primary amines, H2NR, double substitution reactions yielding tertiary (−C6F4)2NR amine bridges were observed, which were absent with secondary amine reagents. No reactions were found for attempted modifications of pPFBMA with bromide, iodide, methanethiosulfonate, or thiourea, indicating a highly selective reactivity toward nucleophiles. The versatility of this reactive platform is demonstrated through the synthesis of a pH-responsive polymer and novel thermoresponsive polymers: an oligo(ethylene glycol)-functional species with an LCST in water and two zwitterionic polymers with UCSTs in water and aqueous salt solution (NaCl concentration up to 178 mM).