were further assigned by 1H COSY (Figure -26). Subsequently, four more polyesters (14-17) were synthesized from the diol (HM, 5) in good yields (Scheme 2). The structures of all eight polyesters (10-17) were confirmed by 1D and 2D NMR techniques (Figure , and see the SI (Figure )). After polymerization, the hydroxyl peaks of the two diol monomers completely disappeared, protons attached to the carbon atoms next to the ester group (3, 2'') are highly deshielded (δ=∼5.0, 4.0 ppm), and those close to the carbon 3, 2'' (2', 2, 4) experience a slightly higher deshielding, than the remaining protons of the polymers when compared with those of the monomers (2, 5). Also, it is clear from the NMR spectra that the bicyclic ring structure of the α-pinene is retained. (Figure , and see the SI (Figure -S50)). The structures of the polymers (10-17) were also confirmed by C NMR. Since the (2, 5) possess two types of OH groups (1° & 2°), two ester peaks appeared at δ = ∼160-170 ppm). When both the co-monomers are rigid -achieved by utilizing the dimethyl ester of 2,5-furan dicarboxylic acid as acyl donor -the resulting polyester will be stereoregular (HN_FDCA (10), HM_FDCA ( )). Conversely, when one of the monomers is flexible the resulting polyesters will be atactic (11-13, 15-17). Precisely, 6-membered cyclic structures formed by intramolecular -C-H---O(=C)-Hbonding stabilize the HN_FDCA (10) in a syndiotactic form, and the same type of interaction stabilizes the HM_FDCA (14) in isotactic form, which is evident from the δ of the protons labeled as 4 (endo and exo), 3, 2, and 2''/2' (see SI, Table ). In addition, tail-to-tail, head-to-tail, and head-to-head isomers were also observed for FDCA polymers (10, 14) in a ratio of 1:2:3 for HN_FDCA (10) and 1:2:1 for HN_FDCA (14) as evident from the splitting pattern of the aromatic protons, and carbonyl peaks of the ester groups (Figure , and see SI, (Figure )). All the monomers and polymers were further characterized by FT-IR analysis (See the SI, Figure ). For the monomers HN (2), and HM (5), the -OH peaks were observed at ∼3200-3300 cm -1 , aliphatic and aromatic C-H stretching bands appeared at ∼2900 cm -1, and aliphatic C-O stretching bands appeared at 1030 cm -1 , After the polymerization, the -OH peak at ∼3200-3300 cm -1 completely disappeared and a new peak was observed at∼1720 cm -1 , which corresponds to the ester carbonyl stretching signal. Ester -C-O stretching was observed at ∼1150-1250 cm -1 , and the remaining peaks in the polymers (10-17) are matched with those of the monomers. The number and weight average molar mass (Mn and Mw) and dispersity (Đ) of the polyesters (10-17) measured from SEC are shown in Figure and. The molar mass of the polyesters increased with the increase in the chain length of the diester (11-13, 15-17, Figure ). A decrease in the carbon chain of the diol monomer when shifting from HN (2) to HM (5) resulted in a slight decrease in the molar mass. Although Mn from SEC is slightly lower than those theoretically calculated from NMR (Table ), both are well in agreement with each other. The polydispersity of the polyesters (10-17) was in the range of 1.2-1.8. The thermal stability of the polyesters (10-17) measured by TGA is shown in Figure and Table . All the polyesters (10-17) showed a thermal decomposition above ∼260 o C (T5, measured at 5% weight loss) and they are thermally more stable than the monomers (2, 5). Moreover, the aliphatic polyesters (11-13, 15-17) showed higher higher thermal stability than the co-(-)-α-pinene-FDCA-based polyesters (10, 14) due to the higher molar mass. In addition, the observed char yield (%) for the polyesters (10-17) was ∼0-20 % (Figure , Table ). Thermal transitions of the polyesters (10-17) were evaluated by DSC and are shown in Figure , see the SI (Figure ) and summarized in Table . The glass transition temperature (Tg) of the polyesters (10-17) decreased with an increase in the chain length of the aliphatic diester and the diol monomer, respectively. When both monomers were aliphatic, the resulting polyesters were amorphous and did not show any melting peaks. In contrast to the aliphatic polyesters (11 -13, 15-17), the two co-α-pinene-FDCA-based polyesters (10, 14) exhibit a remarkably high value of Tg (90, 121 °C) and Tm (270, 277 °C), higher than that of the PET (Tg = 70-80 °C, Tm = 250-260 °C) and Table . Molar mass and thermal properties of the monomers (HN (2), HM (5)), and the polyesters (10-17)