The development of polymer electrolyte membranes that are both structurally robust and chemically stable remains a major challenge for advanced thermoplastic materials used in electrochemical energy conversion systems. In this work, poly (vinyl alcohol) (PVA), a semi-crystalline thermoplastic polymer, was chemically functionalized in order to tailor its physicochemical, thermomechanical, and transport properties. This study is distinguished by a unified and systematic comparison of multiple chemical functionalization strategies under identical conditions, enabling a direct evaluation of their effects on structure property performance relationships. The influence of controlled incorporation of functional groups on the structure–property relationship was systematically investigated. Structural characterization by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) confirmed the success of the chemical modification and revealed variations in the degree of crystallinity as well as a reorganization of intermolecular hydrogen bonding. Thermogravimetric analysis (TGA) demonstrated improved thermal stability, with degradation temperatures shifting toward higher values. Tensile mechanical testing showed a significant increase in tensile strength and elastic modulus, indicating a reinforcement effect attributed to enhanced polar interactions within the modified polymer network. Oxidative stability tests further confirmed improved durability under aggressive conditions. Functionalization resulted in reduced water uptake and methanol permeability, accompanied by an increase in ion exchange capacity (IEC). Proton conductivity increased from 0.46 mS·cm−1 for pristine PVA to 13.3 mS·cm−1 for the modified membrane, representing an improvement of approximately one order of magnitude. This enhanced performance is attributed to the increased dielectric constant, induced polarization effects, and the formation of more efficient proton-conduction pathways within the polymer matrix. These results demonstrate that controlled chemical functionalization effectively modulates the crystalline amorphous balance and intermolecular interactions in PVA, leading to significant improvements in thermomechanical performance and transport properties. This study establishes a clear structure performance correlation framework for the design of high-performance thermoplastic membranes suitable for advanced electrochemical applications.
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