Synthesis of novel hyperbranched polymer through cationic ring-opening multibranching polymerization of 2-hydroxymethyloxetane

The cationic ring-opening multibranching polymerization of 2-hydroxymethyloxetane (1) as a novel latent AB2-type monomer was carried out using trifluoromethane sulfonic acid or trifluoroboron diethyl etherate by a slow-monomer-addition (SMA) method. The polymer yield of poly-1 ranged from ca. 58–88%, which increase with the increasing monomer addition time on the SMA method. The absolute molecular weights (Mw,MALLS) and the polydispersities of poly-1 were in the range of 8,000–43,500 and 1.45–4.53, respectively, which also increased with the increasing monomer addition time. The Mark-Houwink-Sakurada exponents α in 0.2 M NaNO3 aq. were determined to be 0.02–0.25 for poly-1, indicating that poly-1 has compact forms in the solution because of the highly branched structure. The degree of the branching value of poly-1, which was calculated by Frey's equation, ranged from ca. 0.50 to 0.58, which increased with the increasing monomer addition time. The steady shear flow of poly-1 in aqueous solution exhibited a Newtonian behavior with steady shear viscosities independent of the shear rate. The results of the MALLS, NMR, and viscosity measurements indicated that poly-1 is composed of a highly branched structure, i.e., the hyperbranched poly (2-hydroxymethyloxetane). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011