Synthesis and end group structure of 2-deoxydextrans prepared via the cationic ring-opening polymerization of an anhydro sugar

1,6-Anhydro-3,4-di-O-benzyl-2-deoxy-β-D-glucose was polymerized using 1-chloroethyl isobutyl ether or cumyl chloride as initiator and ZnI₂ as activator. The resulting polymer contained predominantly α-(1,6) linkages, and the molecular weight distributions were narrow (≤ 1.25). The kinetics of polymerization was first-order with respect to monomer concentration. There was evidence of slow chain transfer at these polymerization temperatures, although the majority of polymer chains contained the initiator fragment. Mass spectra of the polymer revealed that the initiator fragment at the polymer chain end was an isobutyl group, presumably arising from nucleophilic attack of monomer on the methylene unit of the isobutyl group in the initiating cation with loss of acetaldehyde as opposed to attack at the Sp²-methylene carbon. Cyclic oligomers were present in the polymer sample as well and could have arisen from two processes: HCl initiation or a backbiting reaction.