Credit: © 2010 ACS

Altering the macroscopic structure of plastics through specific chemical signals holds great promise for the development of 'smart' materials, for example for coating, packaging or sensing purposes. Wanji Seo and Scott Phillips at the Pennsylvania State University have now devised a strategy for preparing patterned plastics that can depolymerize in response to specific chemical signals1.

The researchers formed the plastics from phthalaldehyde monomers, which polymerize through the formation of acetal groups. Depolymerization of the resulting chain can be induced easily at temperatures above −40 °C by breaking one of the acetal linkers using acid. Adding a functional group to the end of the polymer — 'end-capping' it — can prevent such cleavage and stabilize the polymer up to 180 °C. Seo and Phillips use this endcap dependence to destablize polymers using chemical triggers.

Three poly(phthalaldehyde) polymers were prepared bearing different end-capping groups: an ester moiety that can be cleaved by palladium(0), a silane group that can be cleaved by fluoride and an alkene chain that is stable to both (acting as a control). Each polymer is stable in solution at 25 °C, but those bearing reactive end-groups rapidly decompose on addition of their specific signal — palladium(0) or fluoride.

Seo and Phillips used these polymers to prepare a patterned plastic sheet consisting of a cylindrical fluoride-responsive block surrounded by the non-responsive polymer. The sheet seems homogeneous because of the similarities between the components, but on exposure to fluoride, the central cylinder collapses, altering the shape of the sheet, showing how chemical signals can be used to control structure.