## 2 Results and Discussion
At the same time, the amount of released EtOH increased rapidly in these systems; therefore, the listed catalysts (principally Ti(IV)) appear to be the most effective for the synthesis of APTES-OH oligomers. DBU, TEA and Ph\({}_{3}\)P catalysts are not so effective in the formation of condensation products. In summary, the best conditions to obtain a monomeric product (APTES-OH) are to carry out the reaction at a temperature of 20-25 \({}^{\circ}\)C, without the use of a catalyst. On the other hand, in order to obtain the APTES-OH oligomers with the greatest efficiency, the reaction should be carried out at an elevated temperature (50-90 \({}^{\circ}\)C) with the use of Ti(IV) as a catalyst. For this reason, it was also decided to carry out a synthesis using the Ti(IV) catalyst and to collect the low-molecular-weight EtOH by-product through vacuum distillation for 3.5 h. The analysis results obtained for this sample are presented in the further course of the work. The conversion of EC and the APTES-OH content during the reaction depending on the catalyst used as well as the amount of ethanol released in relation to the EC conversion are shown in Figure 5. One can say that the alcohols of  
Figure 4: The conversion of EC during non-catalyzed synthesis of APTES-OH depending on the reaction temperature (**A**,**B**), the content of APTES-OH (**C**) and ethanol (**D**) in relation to the conversion of EC depending on the reaction temperature. the Si-OEt bond in APTES-OH and its oligomers by hydroxyl group contained in them is the transesterification process. These kinds of processes are sufficiently catalyzed by Ti(IV) alkoxides, e.g., in the case of PET synthesis. Here, we would expect that the catalytic effect of Ti(IV) alkoxide is caused by its coordinate unsaturation, the electrophilicity of metal and the electron-withdrawing effect of the O-Ti bond in the Si=(O)\({}_{2}\)=Ti complex comprising APTES-O-Ti and APTES-OH (Si-OEt bond) molecules. Titanium tetralcoholates exhibited high catalytic activity in Si-OEt hydrolysis shown by [PERSON] et al. [54]. The formation of monomer and oligomeric structures is confirmed by GPC (Figure 6) and MALDI-ToF analyses (Figure 7). Molar mass distribution given by GPC reveals that the formation of monomer and oligomeric structures is more complex than that of GPC. The formation of monomer and oligomeric structures is confirmed by GPC (Figure 7). Figure 5: The conversion of EC (at 30 \({}^{\circ}\)C for (**A**) and 50 \({}^{\circ}\)C for (**B**)) during the reaction depending on the catalyst used, the APTES-OH content (at 30 \({}^{\circ}\)C for (**C**) and 50 \({}^{\circ}\)C for (**D**)) depending on the catalyst and the amount of ethanol (at 30 \({}^{\circ}\)C for (**E**) and 50 \({}^{\circ}\)C for (**F**)) released in relation to the EC conversion. APTES-OH monomer was obtained with satisfactory yield (88%) and selectivity in the case of sample T2 (25 \({}^{\circ}\)C, no catalyst). There are just small amounts of condensation products identified principally as dimers and trimers. On the other hand, when the Ti(VI)-based catalyst was used, and the temperature was elevated in the process up to 50 \({}^{\circ}\)C (C8), the complex, multimodal molar mass distribution was exhibited, and Mn of the product increased significantly, and thus, its ability to form oligomeric (branched) structures. Moreover, the condensation equilibrium was shifted toward higher oligomers (Mn 2500 g/mol), while vacuum distillation of the by-product was applied to the system (C9). The results of the MALDI-ToF analysis confirmed the conclusions drawn previously for the C8 (50 \({}^{\circ}\)C, Ti(IV)) and C9 (+vacuum) products, and it showed the m/z signals belonging to monomer (n1; minor) and oligomers comprising up to 16 and 22 monomeric units, respectively.