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 ( 1 H 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 (T g s) approaching 135 °C and crystalline melting temperatures where applicable. Dynamic mechanical analysis (DMA) probed sub-T g 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) analysis from melt rheology revealed increasing characteristic relaxation times with increasing 4,4′BB content, which was attributed to the linear 4,4′BB stiffening the polymer chain. Increased kinked 3,4′BB content promoted chain entanglement, resulting in a lower entanglement molecular weight and a higher number of entanglements per chain (N/N e ). Similarly, increases in 3,4′BB content improved tensile yield strength and Young's modulus due to a higher polymer density and potentially due to an increase in entanglement density. Finally, scanning electron microscopy (SEM) suggested mostly brittle failure after necking and strain hardening in tensile specimens. As a result, structure-property relationships afforded insight into regioisomer impacts on thermal, rheological, and mechanical performance for bibenzoate-based (co)polyester regioisomers.
All Science Journal Classification (ASJC) codes
- Organic Chemistry
- Polymers and Plastics
- Inorganic Chemistry
- Materials Chemistry