## 1 Introduction  
Poly(methyl methacrylate) (PMMA) is commonly used in fabricating polymer optical fibers (POF). POFs are desirable for their potential in telecommunications applications [1; 2], all-optical switches [3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15], light-driven actuators [16], and sensors [11; 17]. Environmental factors such as temperature, humidity, and sunlight strongly change the polymer's physical and mechanical properties [18; 19]. The operational lifetime of a material depends on interactions with its surroundings. Characterizing their mechanical properties such as Young's modulus under various conditions can be used to model their stability and to determine the proper time for their replacement [19]. Adding dye to the polymer matrix changes its refractive index and enables the fabrication of fiber cores that act as optical waveguides while also imparting a nonlinear optical susceptibility to the material, making it an attractive candidate for fiber-optic-based all-optical device applications [2; 20]. These materials also potentially act as light-actuated shape-shifters due to the DR1 dopant, which is an azobenzene dye with two phenyl rings separated by an azo bond (\(-\)N=N\(-\)) with two isomer states [21]--the elongated trans form and a bent cis form. Upon irradiating with specific wavelengths of light, DR1 undergoes trans-cis and/or cis-trans photoisomerization. The cis-trans transition can also be driven through thermal excitation [16; 22; 23]. Therefore, the dopants can induce photomechanical effects in the host material through a photothermal change in isomer population or direct photoisomerization, which can be used for photoswitching [21; 22]. Heat and light can induce both thermomechanical and photomechanical responses in azobenzene-doped materials that lead to a change in their mechanical properties [16; 23]. In contrast, crystalscan have a larger photomechanical response due to their high molecular density [24], but crystals cannot be fabricated into long lengths of optical fiber. Adding a low-molecular-weight dopant dye to PMMA influences the thermomechanical and photomechanical properties. The addition of dye with sufficient concentration is observed to plasticize the polymer by increasing the free volume of the system [2]. The plasticization decreases the glass transition temperature [25; 26] and Young's modulus [2; 25; 26] of the polymer. However, depending on the conditions, the interaction of dye and host polymer inhibits chain mobility and the free volume while increasing its packing efficiency, which leads to a higher Young's modulus but with lower \(T_{g}\). This behavior is known as antiplasticization [2; 25; 26; 27; 28; 29]. DR1 is a low-molecular-weight molecule; so, it is expected to plasticize the polymer by decreasing its \(T_{g}\)[30] and stiffness [2]. However, as we will show below, we see evidence of antiplasticization. [PERSON] et al. studied the mechanical properties of PMMA such as elastic modulus, yield stress, ultimate tensile stress, and strain at fracture at 20-80 \({}^{\circ}\)C in 20 \({}^{\circ}\)C increments using uniaxial tension and three-point bending tests. They also presented a numerical analysis for identifying the material parameters for elastoplastic and two-layer viscoplasticity constitutive material models. Both tests demonstrated that all parameters were affected by increasing temperature and, at high temperature, (80 \({}^{\circ}\)C) PMMA shows superplastic behavior [31]. [PERSON] et al. demonstrated a method for measuring Young's modulus of materials, including polymers, by processing the image of a bending cantilever beam. To measure the temperature-dependent Young's modulus, they used a controllable oven and estimated the glass transition temperature (\(T_{g}\)) of polymer samples by presenting an equation that explains the behavior of the elastic modulus near \(T_{g}\)[32]. [PERSON] et al.