## 2 Results and Discussion  
### Synthesis of Polyols and Polyurethanes  
The aim of the first part of this study was to obtain poly(\(\varepsilon\)-caprolactone) diols (PCL diols) which could be applied as precursor of further polyurethanes (PUs) synthesis. The polymerization reactions of \(\varepsilon\)-caprolactone (CL) in the presence of diethylene glycol (DEG) and the lipase from _Candida antarctica_ (CA) were conducted at 70 \({}^{\circ}\)C for 14 days. The molar ratio of CL/DEG was either 20:1 (**PCL-1**), 30:1 (**PCL-2**) or 40:1 (**PCL-3**). Reactions were carried out with one level of lipase concentration at the same scale of monomer (100 mg of CA).  
The structure of the obtained PCL diols was confirmed by proton nuclear magnetic resonance (\({}^{1}\)H NMR) or carbon-13 nuclear magnetic resonance (\({}^{13}\)C NMR), Fourier transform infrared spectroscopy (FTIR) and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS) (Experimental Section).  
In the MALDI-TOF MS spectra of the PCL diols, linear macromolecules were observed (Figure 1). The first and most prominent series of peaks was assigned to polyols terminated with a hydroxyl group (residual mass: 15 Da, Na\({}^{+}\) adduct). This series of peaks was differing by 114 Da, which is equal to the mass of the repeating unit of PCL. In addition, low-intensity series of peaks corresponding to macromolecules (residual mass: 31 Da, K\({}^{+}\) adduct) was detected in the mass spectrum. The average molecular mass (\(M_{n}\)) values of PCL diols determined by the MALDI-TOF MS method ranged from 1500 to 2900 Da (polydispersity indexes (_PD_) 1.36-1.89).  
The weight method was used to determine the reaction yield. For the **PCL-1**, **PCL-2** and **PCL-3**, the corresponding yield values were 84%, 73% and 69%, respectively.  
The \(M_{n}\) values of the PCL diols determined by the gel permeation chromatography (GPC) method were 1800 (**PCL-1**), 2400 (**PCL-2**) and 3200 Da (**PCL-3**), respectively, while the _PD_ showed small variations (between 1.42 and 1.63).  
Figure 1: Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS) spectrum of poly(\(\varepsilon\)-caprolactone) diol.  
The PUs were obtained using PCL diols, dihydroxy(polyethylene adipate) (PEAD) as the soft segments, and 1,6-hexamethylene diisocyanate (HMDI) and 1,4-butanediol (BD) as components of the hard segments. 1,4-diazabicyclo[2.2.2]octane (DABCO) was used as the polyaddition catalyst. A two-step melt polymerization procedure was engaged to this process. The isocyanate index (isocyanate to hydroxyl equivalent ratio) was 1.05. The molar ratio of HMDI/BD/PEAD/PCL/DABCO was 2.5:0.9:0.8:0.8:0.01. The \(M_{\
u}\) values of the PUs were evaluated by the viscosity method and were within the range of 58,000-62,000 g/mol (Table 1).  
The chemical structure of the PUs was confirmed by \({}^{1}\)H, \({}^{13}\)C NMR and FTIR (Figures 2 and 3). The data are shown in the Experimental Section.  
Table 1 shows the mechanical properties of the obtained PUs. The fail stress (\(F_{S}\)), stress at 100% elongation (\(S_{100}\)), Shore hardness (\(Sh_{H}\)) and stress at 100% elongation at break (\(\varepsilon\)) of the obtained PUs were determined. As is presented in Table 1, the \(\varepsilon\) was greater than 300%. The obtained materials showed \(F_{S}\) within the range of 13.9-14.7 MPa and \(Sh_{H}\) within the range of 41-44 Shore A degrees.