The team synthesized the material—poly(thiophene-g-NIPAAm)—using a transition-metal-catalyzed controlled radical polymerization method, known as atom transfer radical polymerization (ATRP), to grow poly(N-isopropylacrylamide) chains on the 3-positions of polythiophene. "Growth of the polyacrylamide chains from each polythiophene repeat unit under ATRP conditions allows the synthesis of polythiophene with densely grafted polyacrylamide chains," McCarley says. "The material is exceedingly soluble in water, which bodes well for green chemical approaches for applications of conducting polythiophenes, including spray coatings and sensing in aqueous media." Poly(thiophene-g-NIPAAm) also exhibits a reversible color change and becomes insoluble in water when the material is heated above a critical temperature (30–32 oC). The color of the material is related to the conjugation length of the polythiophene backbone. Below the critical temperature, the polyacrylamide side chains are fully hydrated, coiled, and extended. Above this temperature, the side chains are collapsed in a globular conformation that shortens the conjugation length of the polythiophene backbone. "This work nicely demonstrates how the combination of ATRP of NIPAAm with an electronically active polythiophene can lead to an efficient thermoresponsive sensor," says Krzysztof Matyjaszewski, professor of natural sciences at Carnegie Mellon University, Pittsburgh. "It will be interesting to extend this approach to gels and explore the behavior of poly(NIPAAm) copolymers grafted onto a regioregular polythiophene backbone."
by MICHAEL FREEMANTLE |
August 01, 2005