Synthesis of Poly( <i>p</i> ‐Terphenyl <i>N,N</i> ‐Dimethylpiperidinium)s Using Asymmetric Ketone‐Based Branching Agent

ABSTRACT Poly(aryl piperidinium)s containing both alkaline stable ether‐free aromatic polymer backbone and heterocyclic quaternary ammonium groups are currently considered as one of the best candidates for the development of anion‐exchange membranes. The branching modification strategy allows accelerating the polymerization process and receiving the polymers with high molecular weight and enhanced characteristics. So far, the application of asymmetric branching agents is very limited. In this study, 4‐biphenylyl trifluoromethyl ketone (BTK) was used as AB 2 ‐type structuring monomer in superacid‐catalyzed Friedel‐Crafts polyhydroxyalkylation together with p ‐terphenyl which is B 2 ‐type monomer, and N ‐methyl‐4‐piperidone which is A 2 ‐type monomer. Polymers with different degrees of branching (1.5 and 3 equivalents of BTK) are synthesized. The presence of unreacted terphenyl, revealed by 1 H NMR and wide‐angle X‐ray diffraction, is highlighted, and measures are proposed to prevent its occurrence. On the basis of neutral polymers (NB‐PTP‐1.5 and NB‐PTP‐3), their quaternized counterparts (QB‐PTP‐1.5 and QB‐PTP‐3) with excellent film‐forming properties are obtained. Static light scattering measurements show that the values of molecular weight of different polymers are close, whereas particle size is bigger for a more branched polymer (according to dynamic light scattering analysis). Thermooxidative resistance of quaternized branched polymers is higher than that of linear polymers. Alkaline stability of polymers is confirmed by 1 H NMR.