Synthesis and Characterization of Amorphous Bibenzoate (Co)polyesters: Permeability and Rheological Performance
Document Type
Article
Publication Date
10-2017
Department
Polymers and High Performance Materials
Abstract
Melt polycondensation of bibenzoate dimethyl esters with ethylene glycol enabled the synthesis of polyesters containing linear (4,4'-bibenzoate (4,4'BB)) and kinked (3,4'-bibenzoate (3,4'BB)) repeating units. Novel 3,4'BB:4,4'BB (co)polyesters with ethylene glycol (EG) showed an onset of weight loss (T-ds%) above 350 degrees C. H-1 NMR spectroscopy confirmed 4,4'BB:3,4'BB incorporation, and size exclusion chromatography (SEC) revealed high molecular weights. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) revealed glass transition temperatures (T-g) approaching 121 degrees C, crystallization and melting transition temperatures (T-c and T-m), and sub-T-g beta-relaxations. 4,4'BB incorporation below similar to 45 mol % afforded an amorphous morphology, while 4,4'BB incorporation above 45 mol % induced crystallinity. Melt rheology elucidated the effect of structure on flow behavior, and time-temperature superposition (TTS) revealed distinct flow transitions. TTS analysis also provided insight into the structural influence of regioisomers on fractional free volume (f(g)) and flow activation energies (E-a). Incorporation of the symmetrical 4,4'BB monomer negligibly affected the fg but imparted a stiffer overall chain, resulting in higher E-a. Positron annihilation lifetime spectroscopy (PALS) of the (co)polyesters confirmed a lack of change in free volume through measuring the average free volume of a spherical hole. Determination of oxygen permeability offered fundamental understanding of the relationship of monomer symmetry with gas permeability and free volume in unoriented films; kinked 3,4'BB monomer afforded higher overall barrier in amorphous films. Finally, tensile testing elucidated Young's moduli and yield strengths, confirming (co)polyesters' mechanical similarity to BPA-polycarbonate. Moduli <= 2.7 GPa and yield strengths up to 74 MPa confirmed BB-based (co)polyesters enhanced properties compared to other high-T-g polyesters.
Publication Title
Macromolecules
Volume
50
Issue
19
First Page
7603
Last Page
7610
Recommended Citation
Mondschein, R. J.,
Dennis, J. M.,
Liu, H.,
Ramakrishnan, R. K.,
Nazarenko, S.,
Turner, S.,
Long, T. E.
(2017). Synthesis and Characterization of Amorphous Bibenzoate (Co)polyesters: Permeability and Rheological Performance. Macromolecules, 50(19), 7603-7610.
Available at: https://aquila.usm.edu/fac_pubs/17641