Optically Fixable Shape Memory Polymers

Air Force Research Laboratory, Wright-Patterson AFB, Ohio

Shape memory polymers (SMPs) are stimuli-responsive materials that remember an original “permanent shape” that can be recovered from a temporary fixed shape by exposure to external stimuli such as heat, electricity, moisture, solvent, or a magnetic field. Shape fixing is most commonly observed by heating the polymeric material above a transition temperature that can be the glass transition (Tg), melting (Tm), or crystalline clearing temperature (Tcl). Recent work has demonstrated that polymeric materials with multiple transitions can exhibit two-way shape memory (2W-SM) behavior and so-called triple shape memory in systems possessing both chemical and physical crosslinking.

Directing shape adaptations with light equips a potential user with remote, wireless control — in addition to the potential for spatial control — with masking or holographic exposure. Prior reports of light-activated SMP leverage photo-induced changes to the crosslink density of the network to program and release a desired shape. One prior report specifies a system composed of an interpenetrating network containing up to 10 mol percent of cinnamic acid groups that photo-crosslink when subjected to UV light >260 nm for one hour to “photo-fix” a mechanically elongated shape. Subsequent irradiation with UV light <260 nm for one hour de-crosslinks and releases the fixed shape.

The invention described here relates to the employment of glassy, photo-responsive polymeric materials as optically fixable SMPs in which the shape fixing mechanism is due to non-reactive, photo-induced reconfigurations of the polymer network morphology.

The optically fixable SMPs are capable of rapid optical-fixing with short exposures (<<5 min) of eye-safe 442-nm light. The use of polymeric materials composed of covalently attached photochromic units, such as azobenzene, and the use of light — which is capable of inducing adjustments to the polymer network morphology — is the key to optical fixing.

Although the model material system is liquid crystalline, liquid crystallinity is not a critical requirement for observing shape fixing in these materials. Optically fixable SMPs have been demonstrated in high-performance, azobenzene-functionalized polyimides. The SMPs of the invention also includes the ability to combine thermal and optically fixable shape memory.

For more information, contact Sunita Chavan at This email address is being protected from spambots. You need JavaScript enabled to view it.; 937-904-4635.