# Poly-(3-ethyl-3-hydroxymethyl)oxetanes--Synthesis and Adhesive Interactions with Polar Substrates
## 3 Results and Discussion
In the FTIR spectra presented in Figure 5, O-H stretch (3324 cm\({}^{-1}\)), CH\({}_{2}\) stretch (2966 cm\({}^{-1}\), 2934 cm\({}^{-1}\) and 2880 cm\({}^{-1}\)) and backbone ether C-O-C stretch (1180 cm\({}^{-1}\) and 1047 cm\({}^{-1}\)) bands are present. It is known that isolated OH groups appear at the ca. 3600 cm\({}^{-1}\) wavenumber, whereas hydrogen-bonded hydroxyls appear at lower wavenumbers (3400-3200 cm\({}^{-1}\)) [40]. Thus, the band observed at 3324 cm\({}^{-1}\) proved the presence of intra- and intermolecular hydrogen bonds within the POXs. [PERSON] et al. demonstrated that the partial substitution of hydroxyls in a hyperbranched polymer reduces intramolecular hydrogen-bond formation [41]. No relationship between the reagents ratio in the POX and peak intensities could be seen, because the FTIR measurements were qualitative. On the other hand, it is clear that respective bands in the spectra of 1:5-1:50 occurred at identical wavenumbers, thus proving great similarity in their structures. The MALDI-TOF technique allows for a deeper insight into the morphologies and microstructures of polymers. It allows for the confirmation of the mass of repeating unit and the residual mass related to the end group or core molecule. A detailed analysis of the structure of the obtained POXs was performed with this technique. An exemplary MALDI-TOF spectrum is shown in Figure 6. The distance between the a-a (b-b or c-c) peaks was equal to 116 _m/z_, which corresponds to a repeating unit of poly(3-ethyl-3-(hydroxymethyl))oxetane). All signals were observed as sodium cation adducts. The most intensive series a can be ascribed to the molecules with the TMP core. The b series _m/z_ values were lower by 18 and can be ascribed to the macromolecules that contained one cyclic structure T\({}^{\prime}\) formed via the dehydration of the terminal T structure and cyclization (Figure 1) [2]. As the reaction was quenched with ethanol, the c series came from POX macromolecule end-capped with ethoxy group. Other signals were in the minority and may have come from products of water elimination. Figure 5: FTIR spectra of poly(3-ethyl-3-(hydroxymethyl)oxetanes). Theoretical macromolecule weight and size are determined by the amounts and structure of used reagents--the monomer to core ratio. In practice, thstatistical nature of polymerization yields a mixture of products of various shapes, branching degrees and molar masses [42]. The molar mass and dispersity of the synthesized polymers are presented in Table 2. One can see that dispersity grew with the growth of the TMP/EHO ratio. This is in agreement with the nature of the ring-opening multibranch polymerization reaction [14; 43]. The table does not show a clear relationship between the theoretical and observed values of the number-average (\(M_{\rm n}\)) and weight-average (\(M_{\rm w}\)) molar mass. This is not surprising because the GPC technique is considered to be error-burden when using polystyrene as the internal standard, because polystyrene's hydrodynamic radius is different from that of the POX. Difficulties in the reliable determination of true average molar mass of hyperbranched polymers by GPC have been described in the literature [44; 45; 46]. It is commonly agreed that the adhesive interactions of a liquid with a substrate are determined by the surface free energy of the phases, as well as by the interfacial tension between them [36]. It is apparent from Equation (3) that when the interfacial tension, \(\gamma_{\rm SL}\), is equal to zero, the work of adhesion is maximized. The data in Table 3 indicate that water contact angle (\(\theta\)) on the POX film (64-67\({}^{\circ}\)) was lower than that for the reference commercial hot melt adhesive (82\({}^{\circ}\)) and lower than that of polyurethane adhesives (75\({}^{\circ}\)) [47], which resulted from the highly polar character of POX due to a high abundancy of hydroxyl groups; this low water contact angle demonstrates strong adhesive interactions with polar substrates.