2.5. Fourier-Transform Infrared (FTIR) Analysis PCL Diol and PUA

In order to identify the functional groups of synthesized PCL diol and m-PUA, a Fourier-transform infrared (FTIR) spectrometer was used. FTIR analyses were carried out on a NICOLET iS5 FTIR spectrometer (Thermo Fisher Scientific, Waltham, MA, USA) equipped with zinc selenide (ZnSe) plate for iD3 attenuated total reflectance (ATR).

The degree of conversion (DC) of three polymerized PUA and twelve differing printed formulas were obtained by using the FTIR. Each material was measured at three time points, including before polymerization, after printing and after post-curing process. The degree of conversion was calculated for each sample using the following equation:

where A_monomoer is the absorbance at 810 cm⁻¹ before exposure to the UV light, A_polymer is the absorbance at 810 cm⁻¹ after exposure to the UV light, C=O_monomer and C=O_polymer are the absorbances within 1720–1730 cm⁻¹ of carbonyl stretching before and after exposure to the UV light, respectively.