A solution for overcoming the low reactivity of terephthalic acid and isosorbide (ISB) is proposed that uses 1,4cyclohexane dimethanol and ethylene glycol. Using the different reactivities, volatilities, and degree of steric hindrances among the three diols, a highly heat-resistive biobased terpolyester (PEICT; glass transition temperature = 93−143 °C) was synthesized with a high degree of polymerization (weight-average molecular weight 65 400; number-average molecular weight 25 400). After esterification, most of the oligomer end groups were found to consist of ISB, which decreases the overall reactivity of transesterification due to its characteristics. However, this end group changed gradually into ethylene units, which accelerated the transesterification and chain growth in the polycondensation process via chain scission at the carbonyl carbon adjacent to the ethylene unit. To substantiate this mechanism, the Fukui function was used to calculate the reactivity difference between monomers. The sequence distribution was analyzed using 13 C-nuclear magnetic resonance to elucidate the function of each diol unit in transesterification. Finally, a polycondensation process for the PEICT terpolyester is proposed.

The synthetic problems associated with melt polymerizations to form homopolyesters of isosorbide (ISB) and rigid diacids could potentially be solved by using catalyst systems with acetic anhydride (Ac 2 O). A catalyst consisting of dibutyltin oxide, germanium oxide, and Ac 2 O exhibited excellent performance characteristics in syntheses of a highmolecular-weight homopolyester of ISB and cis/trans-1,4-cyclohexanedicarboxylic acid (CHDA), also referred to as poly(isosorbide cis/trans-1,4-cyclohexanedicarboxylate) (PICD). The acetylation of ISB using Ac 2 O during esterification decreased the steric hindrance of ISB and accelerated the chain growth of PICD. Gel permeation chromatography data confirmed the formation of a highmolecular-weight PICD (71 100 weight-average molecular weight and 14 300 number-average molecular weight) using 0.02 mol of Ac 2 O. The glass transition temperature of PICD was almost 131°C at 0.02 mol of Ac 2 O and decreased with increasing amounts of Ac 2 O due to the breaking of the rigid ring of ISB at higher concentrations of Ac 2 O. The structure of opened ring ISB was confirmed using two-dimensional nuclear magnetic resonance (NMR) and distortionless enhancement by polarization transfer NMR. ■ INTRODUCTION1,4:3,6-Dianhydrohexitol, a biobased material that can be derived from biomass such as wheat, sugar, and corn, has been used in various polymer preparations, pharmaceuticals, and cosmetics. 1−6 It has three stereoisomers which are isosorbide (ISB), isomannide, and isoidide, respectively obtained from glucose, mannose, and fructose. 7,8 Among its three stereoisomers, ISB is the most easily accessible and affordable monomer for polymer synthesis 8,9 and is one of the most favorable candidates for renewable monomers used in addressing environmental issues and the depletion of petroleum resources. 10 When ISB is used as a monomer of polyester, the resulting polyester is not only environmentally desirable, but also has superior thermal and optical properties due to its molecular rigidity and the chirality of its asymmetrical hydroxyl groups. Several reports describe attempts to synthesize various polymers containing ISB, including polyesters, 11−24 polyurethanes, 25−29 epoxy, 30,31 polyamides, 32,33 polycarbonates, and liquid crystalline polymers. 34−38 In homopolyesters made with ISB, the incorporation of terephthalic acid (TPA), an aromatic diacid, results in materials with high thermal stability and desirable mechanical properties. However, the formation of a homogeneous system during polymerization is problematic because both TPA and ISB are solid powders and TPA does not dissolve in ISB melts. 13 Furthermore, the low reactivity and volatility of ISB make it difficult to obtain a high-molecular weight polymer. Previous studies by Quintana et al. 10 describe syntheses of polyterephthalates from ethylene glycol (EG), 1,4-cyclohexanedimethanol (CHDM), and ISB. They reported the number-average molecular weights (M n ) and weight-average molecular weights (M w ) of PE(CIs)T terpolyester conta...

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Poly(1,4-cyclohexanedimethylene isosorbide terephthalate) (PICT) copolymers were synthesized by melt condensation with various contents of the corn derived monomer isosorbide (ISB). Since poly(1,4-cyclohexanedimethylene terephthalate) (PCT) has disadvantageous thermal processing properties as well as a high melting temperature, ISB could be used to control T g and T m simultaneously. An increased content of ISB can increase the T g and lower the T m by affecting the crystallization behavior and structural properties of PCT. The composition of PICT was confirmed using 1 H-NMR spectroscopy, and the detailed structure was analyzed with correlation spectroscopy (COSY) and heteronuclear single-quantum correlation spectroscopy (HSQC). 13 C-NMR spectroscopy was used for investigating the sequence distribution and from these results, the effect of the ISB-TPA dyad on the thermal properties was revealed. Solid state cross polarization/magic angle spinning (CPMAS) 13 C-NMR spectroscopy was used to investigate the free space of an atom due to environment dependent relaxation behavior, which determines whether ISB is excluded from the crystal structure. Then, WAXD was used to analyze the crystal structure, representing the effect of ISB on the crystallization. Finally, polarized optical microscopy and atomic force microscopy were used to visualize the morphological change of the crystallite resulting from ISB. † Electronic supplementary information (ESI) available. See