The dispersion of praseodymium phosphate (PrPO4) nanoparticles (NPs) can be beneficial in providing luminescent features and prolonging the lifetime of high-performance interpenetrating polymer networks based on poly(methyl methacrylate)/poly(urethane) (PMMA)/(PU), under Ultraviolet light and humidity. This chapter evaluates the structural, morphological, thermal, and mechanical effects of incorporating PrPO4 NPs of rod and semi-spherical morphologies. The dispersion analysis, through the visible region emission of PrPO4 NPs, by confocal laser scanning microscopy (CLSM), is performed to detect how the NPs are incorporated. Also, structural analysis of PMMA/PU and PrPO4 is achieved through Fourier transform infrared analysis (FT-IR) to known interactions and detect polymerizations of both phases. The hydrophilic or hydrophobic nature of PMMA/PU/PrPO4 and thermal stability is studied by contact angle and thermogravimetric (TGA) and differential scanning calorimetry (DSC) analyses. The tensile test, which determines the potential use of nanoindentation to evaluate the properties after being subjected to accelerated weathering conditions, is discussed. Results demonstrated that semi-spherical NPs provide tensile strength, whereas rod NPs impart ductility to PMMA/PU IPNs. Nanomechanical properties are prolonged with the addition of rod NPs during accelerated weathering essay. This makes PMMA/PU/PrPO4 IPNs attractive materials for outdoor applications where mechanical properties must be preserved.