Self-Controlled Synthesis of Hyperbranched Poly(ether-ketone)s from A(2) + B-3 Approach in Poly(phosphoric acid)

Abstract

Self-controlled synthesis of hyperbranched poly(ether-ketone)s (HPEKs) were prepared from "A(2) + B-3" approach by using different monomer solubility in reaction medium. 1,3,5-Triphenoxybenzene as a hydrophobic 13,3 monomer was reacted with commercially available terephthalic acid or 4,4'-oxybis(benzoic acid) as a hydrophilic A(2) monomer in a hydrophilic reaction medium, polyphosphoric acid (PPA)/phosphorous pentoxide (P2O5). The resultant HPEKs were soluble in various common organic solvents and had the weight-average molecular weight in the range of 3900-13,400 g/mol. The results implied that HPEKs were branched structures instead of crosslinked polymers. The molecular sizes and shapes of HPEKs were further assured by morphological investigation with scanning electron microscopy (SEM) and atomic force microscopy (AFM). Hence, the applied polymerization condition was indeed strong enough to efficiently facilitate polycondensation via "direct" Friedel-Crafts reaction without gelation. It could be concluded that the polymer forming reaction was kinetically controlled by automatic and slow feeding of the hydrophobic B-3 monomer into the hydrophilic reaction mixture containing hydrophilic comonomer. As a result, hyperbranched structures were formed instead of crosslinked polymers even at full conversion (equifunctional monomer feed ratio).