Hyperbranched Polyfluorinated benzyl ether polymers: Mechanism, kinetics, and optimization

Abstract

Highly fluorinated, hyperbranched polymers were synthesized from the polycondensation of AB 2 monomers, 3,5-bis[(pentafluorobenzyl)oxy]benzyl alcohol and 3,5-bis[(pentafluorobenzyl)-oxy]phenol with potassium carbonate base, and 18-crown-6 phase transfer agent in a variety of polar aprotic solvents. The regioselectivity of the polymerization was optimized and was found to be temperature dependent. The new polymerization technique produced higher molecular weight polymer using safer conditions than earlier methods. The resulting optimization was used to control substitution of oxygen-bearing nucleophiles along nonactivated fluoroaryl systems in high yield. Water was found to induce side reactions that generate a highly conjugated fluoroaryl phenol with lowered reactivity. The removal of a methylene spacer in the polymer backbone of the hyperbranched polymer produced a polymer with greater thermal stability. The reaction conditions for polymerization were found to be general for nucleophilebearing perfluorinated systems. V C 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52,[985][986][987][988][989][990][991][992][993][994]

Synthesis and physical properties of highly branched perfluorinated polymers from AB and AB2 monomers

“…All monomer and polymer syntheses were adapted from methods developed in previous work . Perfluorinated monomers were synthesized by the reaction of 2,3,4,5,6‐pentafluorobenzyl bromide with the corresponding aromatic alcohol using K 2 CO 3 as base and 18‐crown‐6 as phase transfer agent in acetone.…”

“…All polymerizations were carried out at room temperature to control nucleophilic aromatic substitution selectivity. Deprotonation of the benzyl alcohol at room temperature generates an alkoxide anion capable of selective nucleophilic aromatic substitution at the para ‐position relative to the point of attachment for pentafluorophenyl groups; increasing the temperature has shown to lead to unwanted side reactions along the ortho‐ position of pentafluorophenyl rings . This substitution behavior is attributed to the stability of the Meisenheimer complex associated with nucleophilic aromatic substitution (S N Ar) processes .…”

“…This substitution behavior is attributed to the stability of the Meisenheimer complex associated with nucleophilic aromatic substitution (S N Ar) processes . Additionally, the polycondensation of branched perfluorinated aromatic systems becomes increasingly sensitive to water as temperature increases and should remain at room temperature to prevent unwanted crosslinking reactions and gelation …”

“…The polymerization of 1 was adapted from previous methods . Concentration was kept constant for all fluoropolymer polymerizations (0.8 M).…”

“…So far, few papers address poor mechanical properties of hyperbranched polymer membranes while retaining the original AB n monomer system for producing hyperbranched polymers. In recent work, a new route for the polycondensation of perfluorinated, benzyl ether‐linked, hyperbranched polymers was developed . In this work, the copolymerization behavior of fluoroaryl AB 2 + AB systems is examined in an effort to enhance mechanical properties of hyperbranched polymer membranes.…”