We’re investigating a polymer that is composed of many covalently-bonded thermal contractile units. This polymer sets itself apart from others by contracting in response to a small rise in ambient temperature. It’s a very rare occurrence among man-made materials, which usually expand upon heating.

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This new polymer could generate unique properties that otherwise have been unattainable and could entail significant technological ramifications. For example, high-performance electronic devices require electronic-packaging polymers featuring a low coefficient of thermal expansion (CTE). This can be accomplished by embedding thermal contractile units in the existing polymers to act as thermal expansion compensators.

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A bi-layer polymer system in which one layer expands while the other layer contracts can serve as the basis of energy-efficient wearable robots that operate in the physiologically relevant temperature range. This is critical for biomedical applications.

 

The thermal contractile unit, dibenzocyclooctadiene (DBCOD), that we’ve identified, behave as sub-molecular switches. With a flexible eight-member ring flanked by two rigid phenyl groups, this switch –– undergoes a reversible conformational change much like proteins. For DBCOD, heat causes contraction when its thermodynamic global minimum conformation (twist-boat) switches to a local minimum conformation (chair).