*2.1. Materials*

Maleic acid (MA), hexanedioicacid (HA), n-butyl titanate (Ti(OBu)4), methanol, chloroform, and p-toluene sulfonic acid (TsOH) were obtained from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). In addition, 1,4-cyclohexanedimethanol (CHDM), 1,6 hexanediol (HG), eopentyl glycol (NPG), and dibutyltin dilaurate (DBTDL) were purchased from Aladdin Reagents Co., Ltd. (Shanghai, China). Jeffamine® M-1000 was commercialized by Huntsman Corp. (Texas, USA). Waterborne non-ionic hexamethylene diisocyanate trimer (WHDIT, with a -NCO content of 19.5 ± 0.5%) was purchased from Habo Chemical Co., Ltd. (Wuhan, China).

### *2.2. Methods*

### 2.2.1. Synthesis of Linear Polyesters

The mixture of monomers (MA, HA, HG, CHDM, and NPG), catalyst (0.6 mol% with respect to the diacids), and antioxidant 4-methoxy phenol (0.5 wt% related to all reactants) were added to a 100 mL three-neck round-bottom flask, which was equipped with a mechanical agitator, a nitrogen inlet, and a condenser. Firstly, the mixture was stirred at 180 ◦C (760 mmHg) under N2 atmosphere for 5h. Secondly, the pressure of the system was gradually decreased to 0.3–2 mmHg, and the mixture was stirred under vacuum until an apparent Weissenberg effect (the viscoelastic liquids climb up to a rotating rod) was observed. The product was dissolved in chloroform, followed by precipitation with a large amount of cold methanol. Following this, a pale yellow, transparent, viscous, linear polyester was obtained.
