Influence of Bibenzoate Regioisomers on Cyclohexanedimethanol-Based(Co)polyester Structure–Property Relationships

Melt polymerization enabled the synthesis of semi-aromatic (co)polyesters containing 1,4-cyclohexanedimethanol (CHDM), 4,4′-bibenzoate (4,4′BB), and 3,4′-bibenzoate (3,4′BB). Proton nuclear magnetic resonance (1H NMR) spectroscopy confirmed monomer incorporation, and size exclusion chromatography (SEC) revealed molecular weights and polydispersity indices (PDIs) consistent with high conversion melt phase synthesized polyesters. All bibenzoate-based polyesters exhibited a high onset of 5 wt % loss temperature according to thermogravimetric analysis (TGA) (>350 °C), and differential scanning calorimetry (DSC) provided compositionally dependent glass transition temperatures (Tgs) approaching 135 °C and crystalline melting temperatures where applicable. Dynamic mechanical analysis (DMA) probed sub-Tg β-relaxations with minimal changes in intensity, suggesting that cyclohexyl ring relaxations dominated the low temperature energy absorption for all (co)polyester compositions. Time–temperature superposition (TTS...