## 1 Introduction  
The manufacturing conditions of polymeric materials are critical since they determine the resulting polymer structure, and as an outcome, its final properties and performance characteristics [1; 2; 3; 4]. Therefore, it is important to monitor polymers during the fabrication process to enhance our understanding of their relationship to the final quality of the manufactured parts. Ensuring polymers have the required characteristics will help improve their reliability when used in primary structures in fields such as aerospace, automotive, biomedical, electrochemical, etc. When manufacturing polymers, solvents play an important role since they allow for a reduction in the polymer's viscosity during a coating process or assist with the dispersion of fillers into the polymer matrix [5; 6; 7]. This inevitably raises the concern of improperly removing the solvent from the polymer before obtaining its final structure. It has been shown that the incorrect removal of the solvent affects both the physical and chemical properties of polymers [8; 9; 10; 11]. For example, [PERSON] et al. showed that the presence of solvent in sodium dodecyl sulfate decorated graphene hybrid electrically conductive adhesives significantly decreased their lap shear strength due to the presence of voids and bubble formation [12]. [PERSON] et al. experienced a decrease in tensile strength and hardness of 17 and 9%, respectively, when adding 16 wt.% of acetone in an epoxy resin [6]. Their study also showed that having this amount of acetone caused a decline in the epoxy's adhesion strength from 13 MPa to 4.9 MPa, which signifies a reduction of ~62%. In addition, [PERSON] et al. demonstrated that residual solvent content in an epoxy resin affected its curing mechanics and decreased its crosslinking density. This lowered the glass transition temperature (T\({}_{\text{g}}\)) of the resin by ~8.5 \({}^{\circ}\)C when they added 5 wt.% of cellular nanocrystals as a filler due to a decrease in the homogeneity of the material [13]. Since having residual solvent can negatively affect the properties of a polymeric material, it is important to have a precise evaluation method to determine if the solvent is present in the final structure. Destructive testing, which involves using lab-type instrumentation that requires a specific sample preparation and geometry, is mainly performed to characterize the mechanical properties of materials [14; 15; 16; 17; 18; 19; 20; 21]. It has also been used to characterize the curing kinetics of polymeric materials. Tests include dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), tensile testing, lap shear testing, etc. However, this type of equipment cannot be taken in-field to perform in situ testing. Therefore, it has become essential to develop a non-destructive in situ method to evaluate the degree of reaction and the viscoelastic properties of polymers during curing and after they have been manufactured [22; 23]. Acoustics, consisting of the propagation of sound waves, have been used as a non-destructive evaluation method for different types of materials such as metals [24; 25; 26], ceramics [27; 28], and polymers [22; 29], due to their accuracy and sensitivity. Ultrasonics, which involve the use of acoustic waves at high frequencies (20 kHz-100 MHz), can be used to detect small changes in adiabatic moduli with high precision. Therefore, ultrasonics can be implemented to evaluate phase transitions during curing and the physical properties of materials [22; 30]. For example, the ultrasonic pulse-echo method can be implemented to measure the sound speed of a material with a short pulse of ultrasound generated by a transducer, from which elastic constants of the material can be determined [30]. [PERSON] et al. used ultrasonics to monitor the cure state of thermosetting resins and showed how ultrasonic wave propagation was more sensitive to variations in moduli during the vitrification stage of the curing process compared to DSC [31].