BACKGROUND:  Highly cross-linked polymers have been studied for a number of engineering applications for uses such as adhesives, insulators, and electronic packaging. However, highly cross-linked polymers are also known to be brittle and susceptible to cracking. Therefore, self-mending highly cross-linked polymers hold great promise for overcoming this challenge. These polymers could also find use in automobiles, self-healing windows, and the protection of silicon chips. Several methods have been demonstrated for the creation of self-healing materials. For example, thermoplastics can be repaired by thermally melting the damaged material back together. Materials have also been fabricated that have embedded hollow fibers or capsules within the material itself, so that when a crack propagates, small molecules with the capability to repair the crack are released. However, the ability of these types of materials to self-heal multiple times is limited.

INNOVATION:  Researchers at UCLA have identified and reduced to practice a method of making thermally re-mendable polymers. These transparent and colorless polymeric solids, which are composed of two components assembled by the well-known Diels-Alder reaction, can be fabricated without the use of solvent and cured at temperatures ranging from 80 ºC to 120 ºC. Once a crack is propagated in this cured material, the crack can readily be thermally repaired. Upon heating the polymeric body to 120 ºC, many bonds within the material break. Upon slow cooling back to room temperature, these bonds reform in a way that allows for the repair of the fracture. This procedure can successfully be repeated multiple times on the same sample.

POTENTIAL APPLICATIONS 

• May be used in various engineering applications.
• Repairs visible cracks and strengthens the material after a period of use in order to prevent or delay structural failure.

ADVANTAGES

• Can endure multiple cycles of crack mending and structural function recovery.
• The self-mending properties would allow for a longer lifetime than other polymeric materials of similar strength
• Facile fabrication and repair procedures.
• For repair to be successful, does not require additional ingredients such as a catalyst, additional monomer, or a special surface treatment of the fractured surface.
• Hard, tough, and stable at ambient temperatures.
• Most of these solid polymers are transparent.

DEVELOPMENT-TO-DATE:  This invention has been fully implemented, taken from concept to design to practice. Mechanical properties of the material have been tested under a variety of conditions.

Related Papers (Selected)

• "New thermally remendable highly cross-linked polymeric materials." Chen, X.; Wudl, F.; Mal, A.K.; Shen, H.; Nutt, S.R. Macromolecules 2003, 36, 1802-1807.
• "A thermally re-mendable cross-linked polymeric material." Chen, X.; Dam, M.A.; Ono, K.; Mal, A.; Shen, H.; Nutt, S.R.; Sheran, K.; Wudl, F. Science 2002, 295, 1698-1702.

Reference: UCLA Case No. 2002-343

Patent No.: 6,933,361