Fabrication and Mechanical Characterization of Thiol-ene Polymers and Thiol-acrylate Liquid Crystal Elastomers

Patel, Viren
This study's purpose was to synthesize and program thiol-acrylate and thiol-ene based polymeric materials. A Michael addition of dithiol and tetrathiol monomers with a diacrylate mesogen is the single crosslinking mechanism to form a polydomain. A room-temperature-nematic exhibiting local mesogenic alignment, termed polydomain. A strained polydomain with up to 45 mol% excess acrylate composition, allows photocrosslinking reaction forming monodomain elastomers. These polydomain and monodomain stages largely depend on the effects of increment in crosslink density, showing independent mechanical properties. To study mechanical behavior of polydomain and monodomain samples, dynamic mechanical analysis (DMA) was used to investigate linear viscoelastic region, glass transition temperature, isotropic transition temperature and thermal actuation properties. The amount of acrylate associated in LCEs changed mechanical properties of both polydomain and monodomain elastomers. Polydomain samples exhibited reduced transition temperatures, storage modulus, and high strain-to-failure with increased acrylate as a result of reduced crosslink density. Whereas, monodomain have higher transition temperatures, storage modulus, and reducing strain-to-failure with increased acrylate due to increased crosslink density. A tetrathiol monomer with triene is sole crosslinking mechanism to form radical thiol-ene network polymer. The evolution of mechanical properties is analyzed as a function of UV exposure, where ultraviolet light initiates radical reaction. Thiol-ene polymers were successfully prepared through photochemical reaction with up to 80 mol% excess thiol (relative to acrylate) to form glassy polymer networks with chemically function surfaces. DMA was used to investigate the viscoelastic region and glass transition temperature. Increased thiol concentration resulted in reduced glass transition temperature.
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