Synthesis of Photo-Healable and Thermal Shape-Memory Disulfide Polymers

Combining multiple stimuli-responsive functions into one polymer results in a more versatile structure capable of fulfilling more functions than singularly stimuli-responsive polymers. This research aims to synthesize stimuli-responsive polymers with shape-memory and self-healing capabilities. To do this, cross-linked polymers were synthesized with disulfide bonds and tested. Each test was run on 5 films for 3 different crosslink densities (15 total). Films were then exposed to UV light at a wavelength of 320−390 nm and intensity of 2000 mW/cm² for 5 min. When exposed to UV light the disulfide bonds broke and the material became fluid allowing damage to be corrected. Films had healing efficiencies >95% for scratches up to 50% of their thicknesses. To test the shape memory component the poly-disulfide network was heated to 80°C. A force of 0.10 N was applied. The films were then cooled to 25°C and held at temperature for 1 min. The force was then removed. After 1 min the polymer was reheated to 80°C and held for 1 min before being allowed to cool to room temperature. The recovery ratio (R_r) is given as percentage of strain recovered ((ε_m – ε_r  /ε_m ) X 100). All films had recovery ratios >95%. In conclusion, reactions to multiple stimuli can be integrated into one material effectively. This material would have many commercial applications especially as a coating.