## 1 Introduction  
Styrene-divinylbenzene (S-DVB) copolymers are widely employed in various applications due to their chemical robustness, thermal stability, and tunable porosity. Thesecrosslinked polymers serve as versatile platforms for ion exchange resins, adsorbents, and catalysts, particularly in fields such as water purification, chromatography, and catalysis [1; 2; 3]. However, the intrinsic hydrophobicity and limited functional diversity of the base S-DVB matrix often necessitate chemical modification to enhance selectivity, reactivity, and biocompatibility [4]. Incorporating biologically active or heterocyclic compounds into S-DVB matrices has proven effective in enhancing their physicochemical properties. Among such modifiers, 5-hydroxy-6-methyluracil (HMU)--a derivative of uracil--is of particular interest due to its hydrogen-bonding capability, antioxidant activity, and nucleobase-like structural features. These properties open avenues for molecular recognition, metal ion coordination, and biological interfacing [5; 6; 7]. The functionalization of S-DVB with HMU is expected to introduce hydrophilic groups and aromatic nitrogen heterocycles, thereby altering the surface chemistry and potentially the sorption characteristics, swelling behavior, and thermal stability of the polymer matrix. Previous work has shown that nucleobase-modified polymers exhibit enhanced metal-binding capacities and increased interaction with biomolecules [8; 9], suggesting that similar enhancements may be observed upon HMU grafting.  
Other researchers have been interested in studying two-dimensional network supramolecular structures [1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14]. The use of HMU modifying the S-DVB copolymer at different percentages of the supported modifier is very important to constitute supramolecular network structures used for selective adsorption of several molecules [14; 15; 16].  
Knowing that the surface properties of polymeric materials are of paramount importance in applications ranging from chromatography and sorption technologies to biomedical and catalytic systems [17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30], it is therefore crucial to determine these properties, such as the surface energy components, particularly the London dispersive (\(\gamma^{\rm d}\)) and specific polar (\(\gamma^{\rm s}\)) contributions, that govern a material's interactions with gases, liquids, and biological species [31; 32; 33; 34; 35; 36]. Precise characterization of these components is essential for understanding interfacial phenomena, such as adhesion, wettability, sorption behavior, and chemical reactivity [37; 38; 39; 40; 41].  
Inverse gas chromatography (IGC) has emerged as a powerful and sensitive technique for assessing the thermodynamic surface properties of solids, especially polymers, in their native dry state. Unlike traditional techniques such as contact angle measurements, IGC enables the evaluation of surface energy under well-controlled and reproducible gas-solid interaction conditions, even for porous, irregular, or finely powdered materials [42; 43; 44; 45; 46; 47; 48; 49; 50; 51].  
In this study, we investigated the London dispersive and specific polar components of the surface energy of a styrene-divinylbenzene (S-DVB) copolymer modified by 5-hydroxy-6-methyluracil at different percentages. Using inverse gas chromatography at infinite dilution (IGC-ID), by applying our new methodology [40; 41; 52; 53; 54; 55], we determined the surface free energy parameters, assessed the acid-base character of the surfaces, and examined how HMU grafting affects the thermodynamic affinity of the polymer toward various probe molecules. This analysis provided critical insight into the physicochemical transformation of S-DVB surfaces following functionalization and their potential suitability for selective adsorption, separation, or biomedical applications.