2.3. Synthesis of TPEEs Using SOFA as CE

For the synthesis of TPEEs melt polycondensations of NDC and BDO (or BDO/SOFA mixture), and PTMEG were performed in a 600 mL high-pressure stainless steel reactor (Parr Instrument Co., Moline, IL, USA) equipped with a vacuum pump and Dean–Stark apparatus for collecting the by-products [21,22]. TBT (0.3 wt% with respect to NDC) and Irganox 1010 (0.5 wt% with respect to the total mass of monomers) were used as a catalyst and as a thermal stabilizer, respectively. Typically, 33.75 g (0.17 mol) of NDC, 27.53.6 g (0.23 mol) of BDO, TBT (0.15 wt% with respect to NDC), and Irganox 1010 were introduced into the reactor under nitrogen flow. The molar ratio of NDC to CE was maintained at 1:1.5. The transesterification reaction was carried out under a nitrogen atmosphere in the temperature range 160–210 °C for 90 min. By-product methanol was collected and was used to measure the conversion of the transesterification. After the cessation of methanol distillation, 16.67 g (0.016 mol) of PTMEG was added to the reactor along with TBT (0.15 wt% with respect to NDC) as a catalyst. For the polycondensation reaction, the temperature was increased to 250–255 °C, and some of the excess byproduct BDO was distilled off at this stage. Then, the reactor temperature was raised to 260 °C under a high vacuum (0.5 torr), and held for an additional 2h. The resulting TPEEs were dissolved in chloroform at 50–60 °C and purified by precipitating from excess diethyl ether and then was washed with ethanol and vacuum dried at 60 °C for 12 h. Detailed compositional variations are shown in Table 1.

Compositions and thermal properties of TPEEs with different hard and soft segments synthesized by using 1,4-butanediol (BDO) or BDO combine with soybean oil-originated fatty acid diethanolamide (SOFA) as chain extender formulation.

¹ Mole percentage of SOFA with respect to BDO in feed and in polymer (determined by ¹H NMR spectroscopy). Note that [CE]/[NDC] ratio is fixed at 1:1.5. ² Glass transition temperatures of soft phase (T_g1) and amorphous part in crystalline hard phase (T_g2). Note that T_g1 is almost unchanged according to compositional change. ³ Melting (T_m) temperatures, and enthalpies of melting (ΔH_m), measured by DSC. ⁴ Intrinsic viscosity (η) and viscosity-average molecular weight (M_v) measured by Ubbelohde-type viscometer.