## 3 Results and Discussion
### MALDI-TOF Analysis  
Although the MALDI is a technique that can be interpreted only in a semi-quantitative approach and the mechanism of ionization is not yet known entirely, the ionization techniques, such as electrospray ionization (ESI) and MALDI, have the advantage of analyzing intact polymer/oligomer molecules, avoiding fragmentation reactions. It is a soft ionization technique and the polymer/oligomer is not influenced by the solution preparation methods. Once the technique is carried out in a solid state (the solvent must be evaporated in the sample preparation), the sample preparation has a short time. It has considerably high sensitivity, and also, MALDI is a suitable technique to characterize factors such as the polydispersion, data of the repeat units, impurities, and additives in synthetic polymers. It can also be applied to a considerable range of polar and non-polar polymers with an extensive range of molecular masses [35; 36; 37; 38; 39]. In previous times, before the ionization sources coupled with mass spectroscopy, there were not many techniques able to evaluate mass distribution in polymer samples. The secondary ion mass spectrometry (SIMS) and field desorption (FD) could give information about the mass distribution but with a considerable limitation, in that the polymers must be soluble and with maximum molecular mass near to \(10\times 10^{3}\) Da-mol\({}^{-1}\)[40]. NMR spectroscopy and chromatography techniques can provide information about the molecular structures and molecular size, but the distribution concerning chain sizes cannot be fully understood with these methods for a large range of synthetic polymers [41]. To observe the composition of the resins with respect to molecular size, the photoresists were evaluated by MALDI-TOF in view of their oligomer content. There is no influence of the solvent  
Figure 7: TGA of photo resins. content and catalyst, the range of molar size of these compounds is low compared to the range applied in this analysis. The major composition of oligomers present in the samples corresponds to the dimer (region of 715 Da) and trimer (region of 1067 Da) molecules, as Figure 8 shows. Although the major compounds are the same, there are distinct profiles in the samples (e.g., in the mass profile of sample EPR-S2_f are several mass peaks that are not observed in the spectra of the other samples). These differences are due to the synthesis procedure applied. Observing with more details, the range of low-mass spectra (Figure 9, region between 500 and 800 Da), the samples can be separated into groups: the samples EPR-S2_c and EPR-s2_f; samples EPR-S2_b and EPR-S2_e; samples EPR-S2_a, EPR-S2_g, and EPR-S2_h; the sample EPR-S2_d; and finally, the EPR-S1 series. The samples EPR-S2_c and EPR-S2_f presented several mass peaks in the low-mass region, meaning that the polymer chains vary (high polydispersity) or/and had several secondary products. The samples EPR-S2_b and EPR-S2_e are composed mostly of dimers and trimers of the same size approximately. Also, among the samples EPR-S2_a, EPR-S2_g, and EPR-S2_h, the spectral profile is similar. The compositions of sample EPR-S2_d and the EPR-S1 series consist mostly of dimer molecules. These differences in molecular size distribution might result directly in different physical-chemical properties. Moreover, in the spectra, it is also possible to observe several peaks that represent the oligomers in different compositions regarding the bonds with the epoxy groups. The theoretical possibilities are monomer two possible peaks; dimer four possible peaks (see Figure 10 using the dimer as an example); trimer six possible peaks; tetramer eight possible peaks; pentamer ten possible peaks; and hexamer twelve possible peaks. Figure 8: Matrix assisted laser desorption ionization time of flight (MALDI-TOF) of the photo resin samples. These possibilities do not consider the secondary products that can be generated during the epoxidation step. As a result, the molar mass can vary around 30%.