## 2 Materials and Methods
### Measurements  
The solid-state nuclear magnetic resonance (SSNMR) spectra ware recorded on a Bruker III 400 M spectrometer (Rheinstetten, Germany) equipped with a solid-state high-resolution apparatus. The conventional cross-polarization/magic angle spinning (CP/MAS) method was used for high-resolution solid-state \({}^{13}\)C measurements, and the spinning rate was 12 kHz.  
Fourier transform infrared spectra were recorded on a PerkinElmer Fourier transform infrared reflection (FTIR) spectrometer Spotlight 400 N (Shelton, FL, USA)with a scanning step of 2 cm\({}^{-1}\) and accumulation of 8 scans. Both the KBr tableting method and universal attenuated total reflectance accessory (UATR) were applied. For the KBr tableting method, the sample was mixed with KBr powder in a proportion of 1:100-1:200 and the total weight was controlled to 200 mg. For quantitative studies, the weight of samples and KBr powder were precisely weighed to 0.01 mg before mixing.  
High-performance liquid chromatography (HPLC) was performed on a Waters e2695 (Milford, CT, USA) series liquid chromatograph system, which was equipped with a diode array detector (DAD) controlled by an Empower chromatographic workstation. A Sunfire C18 (150 cm \(\times\) 4.6 cm, 5 \(\upmu\)m) was adopted for the analysis. The mobile phase consisted of acetonitrile (chromatopnically pure, 70%) and ultrapure water (30%) using an isocratic elution. The mobile phase was set at a flow rate of 1.0 mL/min and the column temperature was conditioned at 25 \({}^{\circ}\)C.  
The Liquid-state nuclear magnetic resonance (NMR) spectra were measured on a Bruker Avance III 400 M with BBO probe (Rheinstetten, Germany). Samples were dissolved in deuterated chloroform (CDCl\({}_{3}\)) using tetramethylsilane (TMS) as the internal reference at room temperature.  
Dynamic mechanical analysis (DMA) was performed in a tension mode using NETZSCH DMA 242E (Selb, Germany) from room temperature to 300 \({}^{\circ}\)C at a heating rate of 2 \({}^{\circ}\)C min\({}^{-1}\) and a frequency of 1 Hz in air. The specimen dimensions were about 15 mm \(\times\) 5 mm \(\times\) 0.4 mm.  
Figure 1: The curing procedure.  
Melt viscosity (MV) was measured on a Brookfield CAP2000+H (Toronto, ON, Canada) at 171 \({}^{\circ}\)C and with spindle rotating speed 23 rpm. The minimum readings within 60 s were recorded as the MV.  
Dielectric constant and dielectric loss were tested using an Agilent Technologies ENA series network analyzer (E5071C, Santa Clara, CA, USA) with the split-post dielectric-resonator (SPDR) at 10 GHz, 50% relative humidity, and room temperature. Before testing, each sample with thickness about 0.4 mm was dried in a 110 \({}^{\circ}\)C oven for 1 h and then cooled to room temperature in a desiccator for 30 min before testing.  
Differential scanning calorimetry (DSC) curves were obtained with a NETZSCH DSC 214 (Selb, Germany)from room temperature to 300 \({}^{\circ}\)C under a nitrogen atmosphere with a heating rate of 2 \({}^{\circ}\)C\(\cdot\)min\({}^{-1}\).  
Free volume was obtained by positron annihilation lifetime spectrum (PALS, DPLS3000, Anhui, China). There were two identical samples of the size at 1.5 mm \(\times\) 10 mm \(\times\) 10 mm in a 1.1 \(\times\) 106 Bq \({}^{22}\)Na positron source. And a 1.28 MeV \(\gamma\)-ray was emitted by the \({}^{22}\)Na nucleus and the positron within a few picoseconds. The positron lifetime was determined by the time delay between the emission of the birth gamma (1.28 MeV) and an annihilation photon of 0.511 MeV. PALS were obtained using the fast-fast coincidence system. The time resolution was 220 ps and the channel width was 12.6 ps. Program PATFIT was used to process the data and get the lifetime spectra. The positron source components (392 ps/16.40%, 2.05 ns/0.70%) were subtracted before analyzing each spectrum. The variance of the fits was about 1.1.