Ring-opening strategies to hyperbranched polymers

Although the first examples of hyperbranched polymers proposed by Flory involved condensation-type polymerization strategies, the first well-characterized hyperbranched example involved the ring-opening polymerization of 2-carboxylic-2-oxazoline derivatives. As early as 1988, Odian and Tomalia [2] reported the ring-opening polymerization of these derivatives to form random 

Suzuki et al. [14] reported the Pd-catalyzed ring-opening polymerization of a cyclic carbamate in the presence of an initiator, which also acts as a core molecule, to afford a hyperbranched polyamine. The polymerization was proposed to be an in situ multibranching process, wherein the number of propagating chain ends increase with the progress of the polymerization. 

More recently, Kim attempted unsuccessfully to anionically polymerize 2-hydroxymethyloxetane [17]. The failure of such a reaction is most likely due to the fact that oxetanes are not known to ring-open under basic conditions. The 

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