The molar substitution of an acrylic acid (AA) pendant group on a glycidyl methacrylate-methyl methacrylate copolymer was investigated to evaluate its affects on mechanical properties and thermal stability under UV curing. Structural analysis was conducted by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy ((1)H-NMR) to study the synthetic route of the acrylate copolymer. The mechanical behaviors of AA substituted copolymers were interpreted in terms of both their loss tangent and elongation at the break point, because AA increases the cross-linking density, which is directly proportional to the degree of homopolymerization; this relationship was monitored by (1)H-NMR with various molar substitutions. In addition, the optical and mechanical properties of the copolymers were also characterized by the extent of AA molar substitution. The optimal behavior was obtained at a molar substitution of 94.3% (equivalent to an AA/GMA molar ratio of 1.4) and satisfied both the transparency (> 89.3%) and elongation (> 7.4%) requirements for the complex-shaped coatings.