## 2 Experiment
### Preparation and Pre-Polymerization of BADPE  
Experiments were carried out to synthesis bisphenol A dipropargyl ether (BADPE) via the phase transfer pathway using bisphenol A with alkylynyl bromide in a nucleophilic reaction via Williams' reaction condensation, as shown in Figure 1. Bisphenol A (0.6 mol), tetrabutylammonium bromide (0.1 mol), and NaOH (3.0 mol) were added to a three-necked flask containing 600 mL of deionized water with strong stirring and increasing temperature. Then, propargyl bromide (1.4 mol) was added dropwise after 1 h, when the solution returned to room temperature, after which the solution was heated to 343 K for 8 h at constant temperature. At the end of the reaction, the solid was filtered, washed with deionized water three times, and then washed with isopropyl ether. At the end of the reaction, the solid was first filtered, washed with deionized water 3 times, washed with isopropanol 2-3 times, and then placed in a vacuum drying oven and dried under vacuum at 333 K for 2 h. Finally, a white solid product was obtained. BADPE yield: 97%; melting point: 354 K (DSC method); purity: 99% (HPLC method); 1H NMR (CDCl3, 400 MHz) \(\delta\): 7.15 and 6.86 (m, 8H, aromatic), 4.65 (s, 4H, --CH\({}_{2}\)--), 2.49 (s, 2H, --C\(\equiv\)C--H); FTIR: 3283 cm\({}^{-1}\) (\(\equiv\)C--H), 3036 cm\({}^{-1}\) (Ph--H), 2118 cm\({}^{-1}\) (--C\(\equiv\)C--), 1500-1610 cm\({}^{-1}\) (aromatic), 1219 cm\({}^{-1}\) (Ph--O), and 1018 cm\({}^{-1}\) (CH\({}_{2}\)--O). Figure 1: Synthesis of bisphenol A dipropargyl ether. The resins were pre-polymerized with BADPE prior to blending. The experiments were carried out in a four-necked round-bottomed flask with mechanical stirring and a condenser tube and thermometer. A certain volume of dichlorobenzene was first added to the flask, followed by the incorporation of BADPE. CuCl was used as a catalyst and nitrogen was passed to make the reaction more complete. The reaction mixture was then heated to 458 K for 6 h. After the reaction was completed, the mixture was slowly cooled to room temperature, followed by the addition of a large amount of frozen petroleum ether, after which it was precipitated and isolated. Finally, vacuum drying was carried out for 4 h at 323 K. The pre-polymer BADPE-B was successfully obtained. BADPE was subjected to heat to undergo a Claisen rearrangement (Claisen) to form a B-stage resin with a bichromene structure, i.e., a cyclisation reaction to produce benzopyran, which is further crosslinked via free radical polymerization of the double bond in the presence of heat [16], as shown in Figure 2.  
Using HPLC analysis, 84% of the bichromene structure of the B-stage resin was detected in the BADPE prepolymer. The infrared and hydrogen NMR spectra of bisphenol A dipropargyl ether after 6 h of pre-polymerization at 458 K in a nitrogen atmosphere are shown in Figure 3. By tracking the infrared spectra of the pre-polymerized reactants, it can be seen that after 6 h of pre-polymerization, most of the characteristic carbon-carbon triple-bond peaks of alkylynyl propoxyls in the structure of BADPE (at 2128 cm\({}^{-1}\)) disappeared, indicating that a Claisen rearrangement had occurred. In the hydrogen NMR spectrum of the pre-polymerized BADPE, 64.79 is the methylene hydrogen in the pre-polymerized benzopyran structure, and 55.72 and 66.35 are the hydrogens on the double bond in the benzopyran structure, respectively, which indicates that the benzopyran structure was indeed formed by the pre-polymerization reaction of BADPE. DSC analysis of this prepolymer revealed that the temperatures of the further polymerization reaction of the BADPE prepolymer: the initial temperature (T\({}_{\rm i}\)), peak temperature (T\({}_{\rm p}\)), and final temperature (T\({}_{\rm f}\)) of the curing reaction were 354, 380, and 433 K, respectively, and the exothermic enthalpy of the reaction ((\(\Delta\)H)) was 280 J\(\cdot\)g\({}^{-1}\). The T\({}_{\rm f}\) of the curing reaction of the BADPE pre-polymerization was higher than that of the unpolymerized BADPE.