Phosphonium-containing polyelectrolyte networks (PENs) (P1-P4) were prepared by cyclotrimerization of bis(4-acetylphenyl)diphenylphosphonium bromide (M1) and 1,4-diacetylbenzene (M2) with p-toluene sulfonic acid in various M1:M2 ratios (1,0, 1:1, 1:2, and 1:4). The relative abundance of the PAr4+ units in each PEN was demonstrated to influence thermal stability, alkaline stability, water uptake, surface area, and CO2 uptake in predictable ways. Impressively, PENs with NTf2- counterions (Tf = CF3SO3) did not exhibit 5% mass loss until heating above 400 degrees C. Alkaline stability, tested by challenging a PEN with 6 M NaOH(aq) at 65 degrees C for 120 h, increased with increasing PAr4+ content, which reflected the enhanced reactivity of the HO- anion in more hydrophobic materials (i.e., PENs with lower M1:M2 ratios). The specific surface areas estimated by Brunauer-Emmett-Teller (BET) analysis for these PENs were above 60 m(2)/g under N-2 and nearly 90 m(2)/g under CO2. Notably, P3 (in which 33% of monomers comprise a phosphonium moiety) exhibited a CO2 uptake affinity of one CO2 molecule adsorbed for every phosphonium site. (c) 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 598-604