## 2 Results and Discussion  
Influence of Temperature and Catalysts on the Degree of Polymerization of Hydroxyl-Terminated Alkoxysilane Oligomers  
In order to obtain hydroxyl-terminated alkoxysilane monomer and oligomers, the reactions of a primary amine group of APTES with a five-membered EC were exploited in this work. The reaction proceeds via nucleophilic attack of amine on the carbonyl group  
Figure 2: Scheme of the synthesis of APTES-OH monomer and its (hyper) branched oligomers terminated with a hydroxyl group. in cyclic carbonate structure followed by ring opening of the carbonate to give a product comprising carbamate moiety (Figure 2). This type of reaction is well known in the literature and is also widely used for the synthesis of non-isocyanate PUR [51; 52; 53]. However, the nascent product of the reaction of APTES with EC contains a primary hydroxyl group and three ethoxysilane bonds in each molecule; therefore, it may undergo a consequent reaction based on the exchange of alkoxy substituents on silicon atoms, i.e., ethoxy with APTES-OH. The polycondensation process of the APTES-OH monomer takes place under favorable conditions, which may lead to the mixture of linear and (hyper) branched oligomers as presented in Figure 2.  
For the purpose of the screening of catalysts and conditions that influence the structure of products obtained, the equimolar amounts of the reactants were used, and the reactions were carried out in bulk, without a solvent (1.5 wt% of toluene or xylene was used as an internal standard for GC analysis), without a catalyst at temperatures of 20, 30, 50, 70, 90 and 110 \({}^{\circ}\)C and additionally, with 0.5 wt% of catalyst based on: Sn(II), Sn(IV), Zr(II), Zn(II) and Ti(IV) compounds, as well as following organocatalysts, DABCO, DBU, TEA and Ph3P, at temperatures of 30 and 50 \({}^{\circ}\)C. The list of performed reactions is presented in Table 1.  
The \({}^{1}\)H NMR spectra of the products T2 (25 \({}^{\circ}\)C, no catalyst), C8 (50 \({}^{\circ}\)C, Ti(IV) catalyst) and C9 (50 \({}^{\circ}\)C, Ti(IV) catalyst, vacuum) are shown in Figure 3. The spectrum of T2 (a) reveals signals for methyl (a, 1.2 ppm) and methylene (b, 3.8 ppm) protons in the oxyethylene groups bond to silicon as well as a signal of methylene protons at carbon bond directly to silicon (c, 0.6 ppm) and following methylene groups in propylene chain (d, 1.6 ppm and e, 3.15 ppm). The confirmation of monomeric product structure may be read from the signals of chemical shift at \(\delta\) 4.15 and 3.8 ppm, corresponding to the protons in methylene groups next to oxygen atoms of the formed urethane group (f and f'--in monomer and oligomer structure, respectively) and also hydroxyl group (g, overlapping with signal b), respectively. Moreover, the signals of protons bond to oxygen atoms in hydroxyl (h, 2.78 ppm) and to nitrogen in carbamate (i, 5.18 ppm) groups, correspondingly, are seen clearly. Additionally, there are minute signals at \(\delta\) 4.5 (j) and 2.62 ppm (k) revealing some small amounts of residual EC and APTES. When comparing the \({}^{1}\)H NMR spectrum of T2 with the ones of C8 and C9, one can see that increasing temperature, the introduction of catalysts and arbitrary