2.2.1. Intrinsic Viscosity

The intrinsic viscosity [*η*] of TPAEs was determined by an Ubbelohde viscometer using *<sup>m</sup>*-cresol as solvent with a concentration of 0.5 g·dL−<sup>1</sup> at 25 ± 0.01 ◦C. [*η*] was calculated by the following Solomon—Ciuta equation of a single-point method (Equation (1)).

$$\mathbb{E}\left[\eta\right] = \sqrt{2\left(\eta\_{sp} - \ln \eta\_r\right)}/c \tag{1}$$

where *<sup>η</sup>sp* is specific viscosity, *<sup>η</sup><sup>r</sup>* is relative viscosity, and *<sup>c</sup>* is the TPAE concentration (g·dL<sup>−</sup>1).

#### 2.2.2. Density Measurement

The density of samples was determined using a water displacement method according to *ASTM D792-13*; the density (*ρ*) was calculated by Equation (2):

$$\mathbb{E}\left[\rho\right] = \left(\frac{a}{a-b}\right)\rho\_{water} \tag{2}$$

where *a* is the apparent mass of sample in air, *b* is the apparent mass of sample completely immersed in water, and *ρwater* is the density of water.

#### 2.2.3. Nuclear Magnetic Resonance (NMR)

The TPAEs samples (15 mg) were dissolved in 0.5 mL of deuterated trifluoroacetic acid (TFA-d). 1H NMR and 2D NMR spectra were recorded on an AVANCE-600 spectrometer (Bruker Ascend, 600 MHz, Germany) at ambient temperature using TFA-d as solvent. The chemical shift of the solvent is 11.6 ppm. Two-dimensional (2D) correlation spectroscopy ( 1H-1H COSY) using the standard Bruker pulse program cosygpppqf with the following parameters: spectral width SW1 = SW2 = 11,904.7 Hz, acquisition time 0.086 s, relaxation delay 2.0 s; processing, SI = 1024 (f2, f1), WDW = QSINE.

#### 2.2.4. Fourier Transform Infrared Spectroscopy (FT-IR)

The films of TPAE were analyzed on a Nicolet 6700 spectrometer (Thermo Fisher Scientific, USA) equipped with ZnSe crystal using an attenuated total reflectance (ATR) model. Films were prepared by drop-casting from HFIP and kept at room temperature for 48 h followed by drying in vacuum at 60 ◦C for another 48 h to remove the solvent. The spectra were recorded from 4000 to 650 cm−<sup>1</sup> with a spectral resolution of 4 cm<sup>−</sup>1.

#### 2.2.5. Gel Permeation Chromatography (GPC)

GPC was performed using HFIP as eluent at 40 ◦C on an Agilent PL-GPC50 equipped with a differential refractive index detector. Two PLHFIPgel columns (300 × 7.5 mm, <sup>9</sup> <sup>μ</sup>m) were used. The sample concentration and eluent flow rate were 3 mg·mL−<sup>1</sup> and 1.0 mL·min<sup>−</sup>1, respectively. Calibration of the measurements was carried out with poly(methyl methacrylate) standards.

#### 2.2.6. Differential Scanning Calorimetry (DSC)

Thermal properties of TPAEs were characterized on a Q2000 DSC apparatus (TA instrument, USA). The instrument was calibrated with indium before measurements. A sample was heated to 200 ◦C at a rate of 10 ◦C·min−<sup>1</sup> and held for 3 min under nitrogen atmosphere to eliminate any thermal history. Then, the sample was cooled to −80 ◦C and reheated to 200 ◦C at a cooling/heating rate of 10 ◦C·min−1. The second endothermal curve was recorded to analyze the thermal behavior. The *X*<sup>c</sup> crystalline fraction referring to the amount of PA1212 was calculated according to Equation (3):

$$X\_{\mathbb{C}} = \Delta H\_m / \left( w\_{PA} \Delta H\_m^0 \right) \tag{3}$$

where the ideal enthalpy of fusion of pure PA1212 Δ*H*<sup>0</sup> *<sup>m</sup>* = 292.2 J/g [40].

#### 2.2.7. Wide-Angle X-ray Diffraction (WAXD)

The WAXD measurements were implemented on an X-ray diffractometer (Bruker D8 Advance, Germany) equipped with a Cu Kα radiation source (wavelength *λ* = 0.1542 nm) at ambient temperature. The diffraction patterns were recorded in the range of 2θ from 5◦ to 80◦. Samples with about 0.5 mm of thickness were prepared by casting from HFIP.

#### 2.2.8. Small-Angle X-ray Scattering (SAXS)

Films of TPAEs casting from HFIP solution with about 0.5 mm in thickness were used for the tests. Samples were subsequently annealed under vacuum at 80 ◦C for 12 h to avoid the influence of process history on the morphology. SAXS profiles were obtained from a SAXSess mc2 apparatus (Anton Paar, Austria) equipped with a Cu Kα monochromatic radiation (wavelength *λ* = 0.15406 nm). The measurements were operated at 40 kV and 30 mA at ambient temperature. The scattering intensity (*I*) was obtained as a function of scattering vector (*q*).

#### 2.2.9. Atomic Force Microscopy (AFM)

AFM (Bruker ICON, Germany) was used to investigate the morphology of TPAEs in tapping mode with an Al reflective coated silicon probe (RTESPA, cantilever: <sup>T</sup> × <sup>L</sup> × W = 3.4 × <sup>125</sup> × <sup>40</sup> <sup>μ</sup>m3, 300 kHz, 40 N·m<sup>−</sup>1). NanoScope Analysis software was employed for the data processing. Samples were dissolved dimethylacetamide (DMAc) to acquire 0.2 wt % of polymer solution. Thin films were obtained by drop casting on the silicon wafer followed by carefully evaporating the solvent above 10 ◦C of the crystalline temperature of the samples. Then, all the wafers were immediately isothermal treated for 20 min.

#### 2.2.10. Transmission Electron Microscopy (TEM)

The morphology observation of TPAEs samples was performed on a transmission electron microscope (JEM-1400, Japan); 0.5 wt % sample solutions were prepared by dissolving the TPAEs in DMAc. Thin films were fabricated by dropping the solution on the copper mesh followed by carefully evaporating the solvent above 10 ◦C of the crystalline temperature of the samples. Then, all the samples were immediately isothermal treated for 20 min.

#### 2.2.11. Dynamic Thermomechanical Analysis (DMA)

Dynamic thermomechanical analysis was conducted on a DMA Q800 (TA Instruments, USA) equipped with a liquid nitrogen cooling apparatus. The specimens with a rectangular geometry (30 × <sup>5</sup> × 0.5 mm3) were prepared by casting from HFIP solution. The measurements were performed in the tension mode at a heating rate of 5 ◦C·min−<sup>1</sup> from −100 to 100 ◦C in nitrogen atmosphere at a frequency of 1 Hz. The storage modulus (*E*') and loss factor (*tan δ*) were recorded as a function of temperature for each sample. Furthermore, the temperature of the *tan δ* peak is used to define the glass transition temperature (*T*g) of each sample.

### 2.2.12. Mechanical Properties

Mechanical testing was performed using dumbbell-shaped samples (35 × <sup>2</sup> × 0.5 mm3), according to the guideline of ISO 527-2), which were prepared by casting from HFIP and cut by a mold. The tensile testing was conducted on an Instron 3367 (USA) universal testing machine at a speed of 50 mm·min−<sup>1</sup> at room temperature. Cyclic tensile tests were conducted on a CMT6103 testing machine (MTS, USA). The test specimens were repeatedly exposed to consecutive cycles to a constant strain of 100% (or 200%) with a constant speed of 50 mm·min<sup>−</sup>1. The recovery was measured by observing the residual strain after 10 cycles.
