The PEG based coumarin-2,4-D polymer (3b) was synthesized
from 2 as shown in Scheme 1. To the DCM solution of PEG–
monomethyl ether (Mn – 2000), triphosgene and the coumarin-
2,4-D conjugate (2) were added. The reaction mixture was then
degasied by bubbling with nitrogen gas for 30 min. Aer
degasication the reaction mixture was sonicated for 30 min. A
solution of diethyl azodicarboxylate (DEAD) in dry DCM was
added slowly to the reaction mixture and the reaction mixture
was further sonicated for 40 min. The puried product was then
dried in a vacuum oven overnight. The polymer was characterized on UV and 1H NMR spectroscopy (Fig. S4†)