Polymer, Heal Thyself

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Science  10 Feb 2012:
Vol. 335, Issue 6069, pp. 637
DOI: 10.1126/science.335.6069.637-c
CREDIT: ZHENG AND MCCARTHY, J. AM. CHEM. SOC. 134, 10.1021/JA2113257 (2012)

Damage to a polymer, such as a cut or crack, can be repaired if it's possible to recover the reactive groups that initiate and sustain polymerization. Zheng and McCarthy show that one of the oldest polymerization schemes—the formation of silicones from cyclic siloxanes—can be used in this fashion. An 80:1 mixture of octamethylcyclotetrasiloxane (D4) and its ethylene-linked dimer (bis-D4) was polymerized with an anion initiator by heating at 90°C for 4 hours. The resulting polymers contained active silanolate end groups under ambient conditions. The rubbery material could be cut with a knife and then repaired by holding the pieces in place next to one another and reheating at 90°C for 4 hours. When the repaired material was stressed by bending, it split at a location different from the knife cut. The authors note that this propensity was probably evident ∼60 years ago when these polymerization methods were originally explored.

J. Am. Chem. Soc. 134, 10.1021/ja2113257 (2012).

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