Azide-Capped Poly(alkoxycarbonylmethylene)s for Click Chemistry: Their Syntheses by 2-Bromoethanol-Mediated Chain Transfer Polymerization of Diazoacetate Followed by Azidation

An effective method for incorporating an azide group at an initiating chain end of poly(alkoxycarbonylmethylene) (PACM) is presented. Polymerization of diazoacetate using π-allylPdCl(Py) (Py = pyridine) as an initiator in the presence of 2-bromoethanol as a chain transfer agent (CTA) afforded a Br-capped PACM, which was subjected to nucleophilic substitution with tetrabutylammonium azide (TBAAZ) to yield an N3-capped PACM. The efficient progress of the two-step transformation was confirmed by chain-end characterization with MALDI-TOF-MS analyses. The use of additional pyridine was found to promote the ligand exchange from Pd–Cl to Pd–OCH2CH2Br, thus enabling us to prepare well-defined N3-capped PACMs with Mn in the range of 3000–5000. The utility of the N3-capped PACMs was demonstrated by the preparation of a 4-armed C1-star polymer containing PACM arms via a click reaction of the chain-end azide with a tetra-alkyne-substituted compound.