Influence of Cyclobutane Segments in Cycloaliphatic Decahydronaphthalene-containing Copolyesters

Melt transesterification polycondensation enabled the incorporation of rigid, cycloaliphatic diols (2,2,4,4-tetramethylcyclobutane-1,3-diol) into decahydronaphthalene-containing copolyesters, which resulted in amorphous, optically clear materials. Glass transition temperatures approached 155 degrees C and followed predictable trends using the Fox equation for randomly sequenced copolymers. Dynamic mechanical analysis identified several low-temperature relaxations attributed to the complex motions of the decahydronaphthalate and cyclohexyl rings within the polymer backbone. Furthermore, incorporating cyclobutane rings suppressed the low-temperature local mobility, revealing a strong structural dependence on these relaxations. The rheological simplicity of these nonassociating chains permitted analysis over a large frequency window using time-temperature superposition. As a result, the characteristic relaxation times provided insight into chain dynamics and the propensity for chain entanglements. Finally, positron annihilation lifetime spectroscopy probed hole-free volume and reinforced the trends observed with oxygen permeability measurements

Synthesis and Characterization of Amorphous Bibenzoate (Co)polyesters: Permeability and Rheological Performance

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 (<i>T</i>_d,5%) above 350 °C. ¹H 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 (<i>T</i>_g) approaching 121 °C, crystallization and melting transition temperatures (<i>T</i>_c and <i>T</i>_m), and sub-<i>T</i>_g β-relaxations. 4,4′BB incorporation below ∼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 (<i>f</i>_g) and flow activation energies (<i>E</i>_a). Incorporation of the symmetrical 4,4′BB monomer negligibly affected the <i>f</i>_g but imparted a stiffer overall chain, resulting in higher <i>E</i>_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-<i>T</i>_g polyesters

Influence of Bibenzoate Regioisomers on Cycloheanedimethanol-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) (\u3e350 °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) 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/Ne). 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

Synthesis of Polysulfone-Containing Poly(butylene terephthalate) Segmented Block Copolymers: Influence of Segment Length on Thermomechanical Performance

A facile synthesis of hydroxyethyl-functionalized poly­(ether sulfone) (PESu) oligomers permitted subsequent melt transesterification into segmented block copolymers with poly­(butylene terephthalate). The unique solubility of the PESu oligomers in the melt with 1,4-butanediol and dimethyl terephthalate enabled a systematic study of segment length on thermomechanical properties of the resulting block copolymers. ¹H NMR spectroscopy revealed a compositional dependence on the average segment length of the PBT. Additionally, the concert of NMR spectroscopy, DSC, and DMA highlighted critical segment lengths for crystallization and phase separation. In agreement with a relatively constant <i>T</i>_m and phase separation observed with DSC and DMA, respectively, small-angle X-ray scattering identified a compositionally independent lamellar thickness, while the amorphous layer thickness increased with PESu incorporation. As a result, the complementary analytical techniques provided an understanding of the morphological influence on the thermomechanical behavior of an unprecedented family of high-<i>T</i>_g, semicrystalline, segmented block copolymers