The cationic polymerization of 3-methyl-3-oxetanemethanol was initiated using BF3. OEt2. The low ratio of catalyst to monomer results in a mainly linear or slightly branched polymer, and the high catalyst to monomer ratio leads to a hyperbranched polymer. The hyperbranched polyether yielded is amorphous, and the essentially linear version obtained is partially crystalline. In other words, the degree of branching and the crystallinity of resulting polymers are dependent on the catalyst to monomer ratio. Therefore a new approach to control the crystallinity of resulting polymers in self-condensing ring opening polymerization was developed.