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

A methacrylic polymer undergoing highly efficient para-fluoro substitution reactions\udis presented. A series of well-defined poly(2,3,4,5,6-pentafluorobenzyl methacrylate) (pPFBMA)\udhomopolymers with degrees of polymerization from 28 to 132 and Ð ≤ 1.29 was prepared by the\udRAFT process. pPFBMA samples were atactic (with triad tacticity apparent in 1H and 19F NMR\udspectra) and soluble in most organic solvents. pPFBMA reacted quantitatively through parafluoro\udsubstitution with a range of thiols (typically 1.1 equiv thiol, base, RT, < 1h) in the absence\udof any observed side reactions. Para-fluoro substitution with different (thio)carbonylthio\udreagents was possible and allowed for subsequent one-pot cleavage of dithioester pendent groups\udwith concurrent thia-Michael side group modification. Reactions with aliphatic amines (typically\ud2.5 equiv amine, 50–60 °C, overnight) resulted in complete substitution of the para-fluorides\udwithout any observed ester cleavage reactions. However, for primary amines, H2NR, double\udsubstitution reactions yielding tertiary (–C6F4)2NR amine bridges were observed, which were\udabsent with secondary amine reagents. No reactions were found for attempted modifications of\udpPFBMA with bromide, iodide, methanethiosulfonate, or thiourea, indicating a highly selective\udreactivity toward nucleophiles. The versatility of this reactive platform is demonstrated through\udthe synthesis of a pH-responsive polymer and novel thermoresponsive polymers: an\udoligo(ethylene glycol)-functional species with an LCST in water and two zwitterionic polymers\udwith UCSTs in water and aqueous salt solution (NaCl concentration up to 178 mM)