Considering the beneficial effect of CuO particles on the speed of thermal decomposition and the mass of solid residue formed during HIX pyrolysis, we have expanded research on this issue by synthesizing materials that may contain a much larger amount of this oxide than before, which can also give residual carbonaceous materials extremely rich in metallic copper. As polymeric hosts, carboxylic cation exchangers (CCEs) with -COOH groups having both macroreticular and gel-like structure were used. As a result of the low molecular weight of the aliphatic carboxylic acid (acrylic acid or methacrylic acid) forming the polymeric skeleton, their ion exchange capacity (the number of ionogenic groups per mass unit) is several times higher than the sorption capacity of anion exchangers with trimethyl ammonium functional groups used previously as support for CuO [45; 46; 47]. As regards the synthesis of cationites with a CuO deposit, this has so far only been performed for strongly acidic sulfonic cationic receiving HIX for low-concentration ammonia nitrogen removal from water [48]. A CCE with a CuO deposit has not yet been described, but the stabilization of metallic copper nanoparticles inside the CCE matrix has been reported [49; 50]. CCEs are weakly acidic resins, highly selective with respect to the H\({}^{+}\) ion and in contrast with strongly acidic ones, first of all sorb hydrogen ions from among all cations (in this form, they do not split neutral salts). A small, stoichiometric excess of a strong mineral acid is sufficient to convert the resin into the H\({}^{+}\) form. The degree of ionization of their less-dissociated active groups corresponds to that of acetic acid. The effective pH range is between 6 and 14. A relatively high degree of affinity exists for the earth alkaline metal ions. CCEs are used primarily for the removal of cations from basic solutions (dealkalization, softening of high salinity waters), for the splitting of weakly alkaline saltsof polyvalent cations, and also for the isolation and purification of biochemicals such as antibiotics, vitamins, alkaloids, and enzymes [51; 52; 53; 54; 55]. The use of CCEs for reducing the volume of radioactive waste generated in nuclear power plants was also considered [56; 57]. Given the high sorption capacity of CCEs (which is many times higher than other ion exchange resins), the aim of this work was to synthesize HIXs rich in CuO fine particles and examine their thermal properties compared to pure resins. The research was intended to answer the following questions. How much CuO can be introduced into the skeleton of both cationites, and does the gel-type structure limit the mass of this deposit? Can CCEs containing CuO be used in the H\({}^{+}\) form without losing the deposit? What is the effect of the ionic form of the functional groups (Cu\({}^{2+}\), H\({}^{+}\)) and CuO deposit on the decomposition of both resins under air and N\({}_{2}\) atmospheres? During pyrolysis, will the cracked polyacrylic matrix containing -COOH groups (with oxygen atoms) reduce Cu (II) and create an additional amount of carbon char (as in the case of polystyrene matrix of anion exchange resins)? What is the mass and composition of the solid residue depending on the thermal analysis atmosphere? The research described here concerns the synthesis of HIXs particularly rich in a cupric deposit, shows the effects of various factors on the thermal decomposition of synthesized composite materials, and is also related to an important area of modern research-carbothermal synthesis of metal-char composites, which are forward-looking materials. Thanks to the presence of dispersed metallic copper fine particles within the carbonaceous phase, they represent reagents that can be useful for mediating environmentally important processes.