(AB)<sub>n</sub>-segmented poly(urea-siloxane)s are thermoplastic elastomers (TPE), composed of urea-hard segments and poly(dimethylsiloxane) (PDMS) soft segments. These TPEs form stable elastic networks at room temperature due to hydrogen bonding of the urea units. Upon heating, the physical crosslinks disaggregate and melt processing of the material is possible. Poly(urea-siloxane)s are synthesized via polyaddition of diisocyanates and PDMS-diamines with different chain length in order to provide polymers with different transition temperatures, melt viscosities and mechanical properties. The melt viscosity was further tuned to process the polymers with our melt gradient setup by adjusting the molecular weight.<br/>Bulk polymer gradient materials (PGM) are materials which change their composition and consequently at least one property continuously along one axis. So far PGMs are mainly based on low viscous fluid prepolymers which form covalent irreversible crosslinks upon photo- or thermal polymerization. In order to fabricate PGMs from the melt, a heated syringe pump setup for melt processing up to 200 °C was installed. This setup includes two heatable syringes being connected via metal capillaries to a heated static mixer. From each syringe one molten component can be pumped into the static mixer and finally being extruded into a Teflon mold. The gradient is generated by applying a certain flow profile, resulting in an elastic material with a gradually changing modulus. For the PGM we used two poly(urea-siloxane)s differing in their Young’s modulus, which are based on 1,6-hexamethylene diisocyanate and PDMS-diamines with different chain length. The fabricated PGM was optically visualized via UV-Vis measurements by adding an UV-active dye to the soft component. Determination of the Young’s moduli at distinct measuring points along the sample axis proved the continuously changing modulus from a soft to a stiff material.

Soft-hard polymer gradient materials based on thermoreversible urea-siloxane networks

255th National Meeting (2018)

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