Synthesis and characterization of copolymers containing sequential thioethylene units: Potential engineering thermoplastics
A series of model compounds were synthesized that contained sequential thioethylene units. These model compounds had higher melting points than linear alkanes due to stronger intermolecular interactions at the thioethylene segment similar to PTE. The conformational preferences at the thioethylene segment can be identified by an upfield shift of 0.7 ppm for every [gamma]-gauche interaction at the C-S bonds in [sup 13]C solid state NMR. Some of the model compounds exhibited multiple thermal transitions in both heating and cooling runs. This transition involved complete gauche to trans isomerization at the thioethylene segment in the solid state. Similar to the lower oligothioethylene analogs, this conformational transition requires a lattice expansion and wider spacing between the molecules as identified by WAXD. This lattice expansion causes increased segmental mobility in the samples as confirmed by [sup 13]C and [sup 2]H NMR experiments. Copolymers were successfully synthesized using a simple AA-BB polycondensation reaction. Copolymers with ethylene oxide units as spacers between the thioethylene segments had higher melting points than polyoxyethylene and structures similar to polythioethylene. Polymethylene units break up the packing of the thioethylene segments due to different conformational preferences. All the copolymers exhibited multiple endotherms on heating and a single exotherm on cooling. Unlike the model compounds, the sub-melting endotherms were identified as jump type motion between different conformers in the rigid phase as identified by [sup 13]C CP/MAS, Raman, FT-IR and [sup 2]H NMR analysis. This conformational motion in the solid state provides a route for reorganization into higher melting forms seen as an exotherm in the DSC heating runs before final meeting. This reorganization is confirmed as crystal thickening by SAXD studies without any crystal form modification.
- Research Organization:
- University of Southern Mississippi, Hattiesburg, MS (United States)
- OSTI ID:
- 7181587
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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