2.2.1. 1H- and 13C-NMR Spectroscopy

1H and 13C NMR spectra were recorded using a Bruker, Moccow, Russia) Avance Neo III spectrometer (1H: 400 MHz, 13C: 75 MHz); tetramethyl silane was used as an internal standard. NMR chemical shifts were calibrated using the deuterium signal of CDCl3 (7.26 ppm for 1H and 77.16 ppm for 13C).

#### 2.2.2. Elemental Analysis

Elemental analysis was carried out using a LECO, Moscow, Russia CHNS-932 analyzer.

#### 2.2.3. Gel Permeation Chromatography

The molecular mass of the oligomers obtained was determined by gel permeation chromatography using an ULTIMATE 3000 chromatograph (Dionix Thermo Scientific, Moscow, Russia) equipped with a RefractoMax 521 refractometric detector according to [41].

#### 2.2.4. FTIR Spectroscopy

FTIR spectra in the area of carbonyl valence vibrations (between wave numbers ν = 1600 and 1760 cm−1) of the investigated samples were recorded using an IFS-66/S spectrometer (Bruker, Moscow, Russia) with spectral resolution of 1 cm<sup>−</sup>1. The spectra were normalized with respect to the band at 2860 cm<sup>−</sup>1, corresponding to symmetric vibrations of aliphatic –CH2 groups [42].

### 2.2.5. Differential Scanning Calorimetry (DSC)

Endothermic and exothermic effects in the samples within the temperature range from −100 ◦C to +100 ◦C were recorded using a Mettler Toledo MDSC Q100 calorimeter (Mettler Toledo, Moscow, Russia). Heating and cooling rates were 5 K min<sup>−</sup>1.

#### 2.2.6. Mechanical Tests

Mechanical tests of specimens of the materials obtained were performed with an Instron 3365 (Moscow, Russia) testing machine at the extension velocity υ = 0.417 s−<sup>1</sup> and a temperature of 25 ± 1 ◦C by the standard procedure. The following characteristics were measured: the nominal strength σk (MPa), i.e., the maximal stress per initial specimen cross section; the relative critical strain ε<sup>k</sup> (%); the nominal elastic modulus E100 (stress at the relative strain ε = 100%). The synthesized polymer was subjected to 5 tests.

#### **3. Results**

This section is divided into subheadings. It should provide a concise and precise description of the experimental results, their interpretation, as well as the experimental conclusions that can be drawn.

#### *3.1. NMR Spectra of Functionalized Oligotetramethylene Oxides*

The transformations of the terminal fragments of the initial polyfurites were confirmed by NMR data (Figure 4a–d). In the 1H NMR spectra, the protons of the methylene groups of the initial polyfurites (Mn ~ 1008 g·mol<sup>−</sup>1, Mn ~ 1400 g·mol<sup>−</sup>1) are observed at 1.51–1.62 (O-CH2-C*H*2-C*H*2-CH2-O (a)) and 3.31–3.39 (O-C*H*2-CH2-CH2-C*H*2-O (b)) ppm, respectively. The triplet at 3.56 (c) ppm can be attributed to the terminal hydroxy methylene groups. The signals of the two hydroxy group protons appear at 2.31 ppm (Mn ~ 1008 g·mol−1) or at 2.60 ppm (Mn ~ 1400 g·mol−1). Upon the substitution of hydroxy groups with bromine, these signals disappeared. In addition, the signals attributed to the protons of the methylene groups in the vicinity of halogen atoms were found to be shifted. Further, the substitution of bromine with phthalimide groups resulted in the appearance of phthalimide proton signals in a weak field region (δ = 7.63 ppm and 7.76 ppm), and again a shift of the methylene proton signals in the vicinity of the substituent, in this case, phthalimide, is

observed. In the next step, in OTMO diamine spectra, there are the peaks attributed to the protons of two amino groups (<sup>δ</sup> = 2.87 ppm for Mn ~ 1008 g·mol−<sup>1</sup> and <sup>δ</sup> = 2.67 ppm for Mn <sup>~</sup> 1400 g·mol<sup>−</sup>1). The strong field shift of the signals of the functionalized methylene groups is observed.

**Figure 4.** 1H NMR spectra: (**a**)—with Mn ~ 1008 g·mol−<sup>1</sup> and its derivatives, (**c**) OTMO with Mn <sup>~</sup> 1400 g·mol−<sup>1</sup> and its derivatives; 13C NMR spectra: (**b**)—with Mn ~ 1008 g·mol−<sup>1</sup> and its derivatives, (**d**) OTMO with Mn ~ 1400 g·mol−<sup>1</sup> and its derivatives.

In 13C NMR spectra, at each step of the synthetic route, a shift of the signals of the terminal methylene carbon (c) and (d) can be distinguished (Figure 4b,d). In addition, weak field signals (δ = 123, 132, 134, and 168 ppm) appear in the spectra of OTMO-diphtalimides. These signals disappear after the aminolysis is completed.

Number-average molecular weight (Mn) was determined from 1H NMR spectroscopy by comparing the integration of the end-group proton resonances to the repeating unit proton resonances. The results are presented below.

OTMO-dibromide (Mn = 1134 g/mol): 1H NMR (400 MHz, CDCl3, δ, ppm): 3.35 (br m, 55H, OCH2CH2CH2*CH2*Br, O*CH2*CH2CH2*CH2*O main chain), 1.88 (t, 4H, OCH2CH2C*H*2CH2Br), 1.64 (t, 4H, OCH2C*H*2C*H*2CH2O main chain), 1.55 (br m, 47H, OCH2C*H*2C*H*2CH2O main chain). 13C NMR (75 MHz, CDCl3, δ, ppm): 26.5 (OCH2C*H*2C*H*2CH2O), 28.3 (OCH2C*H*2C*H*2CH2O), 29.7 (OCH2C*H*2C*H*2CH2O), 33.6 (OCH2CH2C*H*2CH2Br), 69.6 (O CH2CH2CH2C*H*2Br), 70.5 (OC*H*2CH2CH2C*H*2O).

OTMO-dibromide (Mn = 1526 g/mol): 1H NMR (400 MHz, CDCl3, δ, ppm): 3.35 (br m, 80H, OCH2CH2CH2C*H*2Br, OC*H*2CH2CH2C*H*2O main chain), 1.88 (t, 4H, OCH2CH2C*H*2CH2Br), 1.64 (t, 4H, OCH2C*H*2C*H*2CH2O main chain), 1.55 (br m, 72H, OCH2C*H*2C*H*2CH2O main chain). 13C NMR (75 MHz, CDCl3, δ, ppm): 26.4 (OCH2C*H*2C*H*2CH2O), 28.3 (OCH2C*H*2C*H*2CH2O), 29.7 (OCH2C*H*2C*H*2CH2O), 33.6 (OCH2CH2C*H*2CH2Br), 69.6 (O CH2CH2CH2C*H*2Br), 70.5 (OC*H*2CH2CH2C*H*2O).

OTMO-diphtalimide (Mn = 1266 g/mol): 1H NMR (400 MHz, CDCl3, δ, ppm): 7.76 (m, 4H, Pthalimide), 7.63 (m, 4H, Pthalimide), 3.65 (t, 4H, -C*H*2CH2-Phtalimide), 3.35 (br m, 51H, OC*H*2CH2CH2C*H*2O main chain), 1.70 (t, 4H, -CH2C*H*2-Phtalimide), 1.55 (br m, 51H, OCH2C*H*2C*H*2CH2O main chain). 13C NMR (75 MHz, CDCl3, δ, ppm): 25.3 (OCH2C*H*2C*H*2CH2O), 26.4 (OCH2C*H*2C*H*2CH2O), 27.0 (OCH2C*H*2C*H*2CH2O), 37.7 (OCH2CH2C*H*2CH2Phtalimide), 69.9 (OCH2CH2CH2C*H*2Phtalimide), 70.4 (OC*H*2CH2CH2 C*H*2O), 123.0 (Pthalimide), 132.0 (Pthalimide), 133.7 (Pthalimide), 168.2 (Pthalimide).

OTMO-diphtalimide (Mn = 1658 g/mol): 1H NMR (400 MHz, CDCl3, δ, ppm): 7.76 (m, 4H, Pthalimide), 7.63 (m, 4H, Pthalimide), 3.64 (t, 4H, -C*H*2CH2-Phtalimide), 3.35 (br m, 76H, OC*H*2CH2CH2C*H*2O main chain), 1.70 (t, 4H, -CH2C*H*2-Phtalimide), 1.55 (br m, 76H, OCH2C*H*2C*H*2CH2O main chain). 13C NMR (75 MHz, CDCl3, δ, ppm): 25.3 (OCH2C*H*2C*H*2CH2O), 26.4 (OCH2C*H*2C*H*2CH2O), 27.0 (OCH2C*H*2C*H*2CH2O), 37.7 (OCH2CH2C*H*2CH2Phtalimide), 69.9 (OCH2CH2CH2C*H*2Phtalimide), 70.5 (OC*H*2CH2CH2 C*H*2O), 123.0 (Pthalimide), 132.1 (Pthalimide), 133.7 (Pthalimide), 168.2 (Pthalimide).

OTMO-diamines (Mn = 1006 g/mol): 1H NMR (400 MHz, CDCl3, δ, ppm): 3.35 (br m, 51H, OC*H*2CH2CH2C*H*2O main chain), 2.87 (br s, 4H, NH2), 2.66 (t, 4H, OCH2CH2C*H*2CH2NH2), 1.55 (br m, 55H, OCH2C*H*2C*H*2CH2O main chain). 13C NMR (75 MHz, CDCl3, δ, ppm): 26.4 (OCH2C*H*2C*H*2CH2O, OCH2CH2C*H*2CH2NH2), 70.4 (OCH2CH2CH2C*H*2NH2, OC*H*2CH2 CH2C*H*2O).

OTMO-diamines (Mn = 1398 g/mol): 1H NMR (400 MHz, CDCl3, δ, ppm): 3.35 (br m, 80H, OC*H*2CH2CH2C*H*2O main chain, OCH2CH2C*H*2CH2NH2), 2.67 (br s, 4H, NH2), 1.55 (br m, 80H, OCH2C*H*2C*H*2CH2O main chain). 13C NMR (75 MHz, CDCl3, δ, ppm): 26.5 (OCH2C*H*2C*H*2CH2O, OCH2CH2C*H*2CH2NH2), 70.6 (OCH2CH2CH2C*H*2NH2, OC*H*2CH2 CH2C*H*2O).

### *3.2. Elemental Analysis*

The data obtained in the course of elemental analysis are provided in the Table 3. The closeness of the indices to the theoretical values confirms the structure of the synthesized compounds.


**Table 3.** Elemental analysis of the synthesized compounds.

#### *3.3. Gel Permeation Chromatography of Functionalized Oligotetramethylene Oxides*

In the determination of the molecular mass of compounds, the retention time was from 4.98 to 5.75 min (Figure 5a,b). The small width of the peaks corresponds to the narrow molecular-mass distribution of the oligomer. The obtained values of the average compound molecular mass agree with the theoretical values (Table 4). Furthermore, NMR spectroscopy and GPC revealed that the Mn values of compounds in both series remained constant throughout the end-group transformations (Table 4).

**Table 4.** Molecular weight characteristics of the compounds determined via 1H NMR spectroscopy, and GPC.


Mn 1—Number-average molecular weight of compounds synthesized on the basis of OTMO with Mn ~ 1008 g·mol−1, Mn 2—Number-average molecular weight of compounds synthesized on the basis of OTMO with Mn ~ 1400 g·mol−1, \*—Retention time, min.

#### *3.4. FTIR Spectroscopy*

3.4.1. FTIR Spectra of Functionalized Oligotetramethylene Oxides

The transformation of the terminal hydroxyls in polyfurites into amino groups was also demonstrated by FTIR spectra (Figure 6).

**Figure 6.** The FTIR spectra for the samples: (**a**) OTMO with Mn ~ 1008 g·mol−<sup>1</sup> and its derivatives; (**b**) OTMO with Mn ~ 1400 g·mol−<sup>1</sup> and its derivatives.

The absorption band at 665 cm−<sup>1</sup> (C-Br) is observed in polyfurite spectra after nucleophilic substitution of hydroxy groups with bromine. At the same time, there are no hydroxyl group bands at 3300–3500 cm−1, usually present in polyfurite spectra. In the OTMO-diphtalimide spectrum, a characteristic imide peak appears at 1720 cm−1. An absorption band of amino groups at 3300–3600 cm–1 is observed in the FTIR spectra of OTMO diamines. The rest of the bands of the intermediates and the end product, OTMO-diamine, are identical to those of the initial polyfurite. Thus, it can be concluded that the main chain structure of the oligomer remained unchanged, and only the terminal groups were involved in the reactions.

#### 3.4.2. FTIR Spectra of the Synthesized Elastomers

The FTIR spectra of the synthesized elastomers are shown in Figure 7a,b. The NH band of urethane can be found at 3350 cm−<sup>1</sup> as a broad absorption. A broad band with the center at 2950 cm−<sup>1</sup> and the one at 2860 cm−<sup>1</sup> were assigned to the CH asymmetric stretching and the symmetric one in the CH2 groups. The absorption bands at 1542, 1454, and 1412 cm−<sup>1</sup> were assigned to the amide−NH stretching. The elastomers synthesized from 2,4-toluene diisocyanate (C-1–C-6) have absorption bands at 1600 cm (aryl ring) and also at 1612 cm<sup>−</sup>1. This band is typical for urethane-containing elastomers synthesized on the basis of this diisocyanate. For elastomers synthesized from isophrondiisocyanate, these bands do not appear.

The analysis of the FTIR spectra in the range of carbonyl stretching vibrations (1600–1760 cm–1) reveals the important features of the structural organization of the synthesized elastomers. It is known that the microphase separation of soft and hard segments of elastomers with urethane hydroxyl hard blocks is characterized by an absorption band at 1695 cm−<sup>1</sup> when using isophorone diisocyanate and 1705 cm−<sup>1</sup> when using 2,4-toluene diisocyanate [43].

The samples synthesized from 2,4-toluylene diisocyanate (Figure 8a,b) in the vibration range of 1600–1760 cm−<sup>1</sup> have a strong absorption band at 1705 cm−<sup>1</sup> that corresponds to the hydrogen bond between the hard segments of the elastomer showing the high degree of microphase separation. With an increase in the molecular weight of the oligodiol used in the synthesis of the epoxyurethane oligomer, the intensity of this band decreases. This fact indicates that the degree of microphase separation decreases with an increase in the molecular weight of oligodiol. In the case of using isophorone diisocyanate, the same

regularity appears (Figure 9). It should be noted that the degree of microphase separation is higher for samples synthesized from isophorone diisocyanate.

**Figure 7.** The FTIR spectra for the samples: (**a**) C-1, C-2, C-3, C-4, C-5, C-6; (**b**) C-7, C-8, C-9, C-10, C-11, C-12.

**Figure 8.** Sections of the FTIR spectra for the samples: (**a**) C-1, C-3, C-5; (**b**) C-2, C-4, C-6.

#### *3.5. Differential Scanning Calorimetry Data*

The thermal properties of the synthesized elastomers were studied by differential scanning calorimetry. First, the samples were heated to 150 ◦C, then cooled to 100 ◦C below zero, kept for 30 min, and heated at a heating rate of 5 ◦C/min. In Figure 10a,b, the reheating thermograms of the samples C1–C12 are shown. The thermophysical properties of the synthesized elastomers are shown in Table 5.

**Figure 9.** Sections of the FTIR spectra for the samples: (**a**) C-7, C-9, C-11; (**b**) C-8, C-10, C-12.

**Figure 10.** DSC-curves of the epoxy urethane samples from: (**a**) C-1, C-2, C-3, C-4, C-5, C-6; (**b**) C-7, C-8, C-9, C-10, C-11, C-12.

**Table 5.** Thermophysical properties of synthesized elastomers.


From the presented thermograms, it can be seen that when using the hardener with a molecular weight of 1000, the glass transition temperature is 5–8 ◦C higher than when using a hardener with a molecular weight of 1400. This is due to an increase in the segmental mobility of polymer chains. On the other hand, the use of a hardener with a higher molecular weight provides the prerequisites for the crystallization of the polymer, which should reduce the segmental activity of the chains.

The elastomers synthesized from isophorone diisocyanate have a glass transition temperature lower by 5–10 ◦C than elastomers from 2,4-toluene diisocyanate. This is due to the lower degree of microphase separation of soft and hard segments in elastomers (Figures 8a,b and 9a,b). In this case, an increase in the degree of microphase separation leads to a decrease in the degree of crystallinity of elastomers. It should be noted that the melting temperature of the flexible phase of all the elastomers except C-7 (there is no melting in sample C-7) is 29–30 ◦C.

#### *3.6. Deformation and Strength Characteristics*

According to the data obtained during mechanical tests (Table 6), the deformation– strength characteristics depend on both the molecular and supramolecular structure of the elastomers.


**Table 6.** Physical–mechanical characteristics of the synthesized elastomers.

The elastomers synthesized from 2,4-toluene diisocyanate show a higher Young's modulus (E100), which is explained by a higher degree of crystallinity of the elastomers. However, elastomers synthesized from isophrondiisocyanate, due to a higher degree of microphase separation of soft and hard segments, are characterized by higher strength characteristics. With an increase in the molecular weight of the used hardener, Young's modulus also increases. Increasing the molecular weight of EUO when using a higher molecular weight OTMO in its synthesis leads to an increase in the deformation characteristics of the cured elastomer.

#### **4. Conclusions**

For the first time, a method has been developed for the synthesis of oligotetramethylene oxides with terminal amino groups, including the initial bromination of oligotetramethylene oxide diols, followed by the Gabriel reaction.

Six epoxyurethane oligomers were prepared using the oligotetramethylene oxide diol with Mn ~ 1008 g·mol−1, Mn ~ 1400 g·mol−1, isophorone diisocyanate, 2,4-toluene diisocyanate, and epoxy alcohol-glycidol.

Twelve elastomers from oligomers with urethane hydroxyl hard segments were prepared using synthesized amines.

For the first time, on the basis of epoxyurethane oligomers, synthesized on the basis of polyethers, crystallizable elastomers have been obtained.

The degree of microphase separation is higher for samples synthesized from isophorone diisocyanate.

It has been shown that the use of new oligoamines makes it possible to obtain elastomers with a controlled degree of crystallinity, which allows them to be used as shape memory materials. At the same time, the glass transition temperature of elastomers −60–70 ◦C allows them to be used in extreme conditions of the far North.

The elastomers synthesized from 2,4-toluene diisocyanate exhibit a higher Young's modulus (E100) due to a higher degree of crystallinity of the elastomers. However, elastomers synthesized from isophrondiisocyanate, due to a higher degree of microphase separation of soft and hard segments, are characterized by higher strength characteristics.

**Author Contributions:** Conceptualization, A.S.; methodology, D.K.; investigation, A.S. and D.S.; resources, N.E.; writing—original draft preparation, A.S.; writing—review and editing, A.S. and D.S.; project administration, V.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** The reported study was funded by RFBR and Perm Territory, project number No. 20- 43-596010. The work was carried out within the framework of the State Assignment (theme state registration number 122011900165-2) using the equipment of the Center for Collective Use "Investigations of materials and substances" of Perm Federal Research Center of the Ural Branch of the Russian Academy of Sciences.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The most significant data generated or analyzed during this study are included in this published article. Further results obtained during the current study are available from the corresponding author on reasonable request.

**Acknowledgments:** The study was performed using the equipment of the Center for Shared Use Studies of Materials and Substances at the Perm Federal Research Center Ural Branch Russian Academy of Sciences.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

