J.Am.Chem.Soc.http://doi.org/38c(2015)

Self-immolative polymers are designed to fall apart in the presence of a specific physical or chemical signal. Typically, cleavage of an end group results in the sequential head-to-tail unzipping of the polymer chain. These materials can serve as effective detection systems because the depolymerization produces multiple copies of the same small molecule and thus amplifies the signal that triggered the process. Although this approach works well in solution, the solid state poses more of a challenge because very few chain ends are located at the surface of an object cast from such a polymer.

Now, a team of researchers at Pennsylvania State University led by Scott Phillips have overcome this limitation by designing a polymer in which each repeat unit — rather than just one chain end — contains a group that can trigger depolymerization. Because each polymer chain is functionalized along its length with these 'detection units', more of them remain accessible at the surface of a solid disk cast from them. Phillips and co-workers studied two different systems — each based on a poly(benzyl ether) backbone — with either fluoride-responsive tert-butyldimethylsilyl (TBS) groups or Pd(0)-responsive allyl groups. Solution studies not only confirmed that these materials could be depolymerized with the appropriate triggers, but also that it occurs through a head-to-tail amplification process rather than the cleavage of each detection unit.

When a polymer with a TBS group on each repeating unit was cast into a disk and placed into a solution of tetrabutylammonium fluoride, it took fewer than 5 hours for it to completely dissolve. In contrast, although a disk made from a polymer with just a single TBS unit at the end of each chain showed signs of some reaction in the first few hours (presumably arising from a small number of end groups at the solid surface), no further reaction was observed and the size of the disk remained unchanged after seven days.