Reaction Under Stress

Significance

The authors show that mechanically sensitive chemical groups make it possible to harness the mechanical forces generated when exposing polymer solutions to ultrasound, and that this allows them to bias reaction pathways to yield products not obtainable from purely thermal or photochemical reactions. The carboxylic acid functions of 1 or 2 were coupled to α-methoxy-ω-amino poly(ethyleneglycol) (mPEG) to yield a series of polymers, 3 and 4, that contained either the trans-BCB linker or the cis-BCB linker, in weight-averaged molecular masses of M_w = 4, 10, 20, 40 and 60 kDa. A dilute solution of polymer 3 or 4 (40 kDa) was sonicated in acetonitrile in the presence of a 500-fold excess of 5 which resulted in the same Diels-Alder adduct.