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ABSTRACT:Hyperbranched polythreitol (1) with different molecular weights (M w,SLS ; 1.18 x 10 4 and 4.79 x 10 4 ) was reacted with trityl chloride in DMF to afford a novel amphiphilic polymer (2) consisting of 1 as the hydrophilic core and the trityl groups as the hydrophobic shell. 2 was tested for its ability to act as a unimolecular nanocapsule toward the water-soluble dye, rose bengal (RB). Their encapsulation and 1 release properties were also evaluated by comparison with the degree of substitution (DS) of the trityl groups, i.e., the hydrophobic shell-density. The polymers were found to have very good unimolecular nanocapsule characteristics even at extremely low concentrations. The average number of RBs per polymer molecule depended on the hydrophilic core size and the hydrophobic shell-density. The increasing DS value led to a decrease in the encapsulated amount due to the decrease in the hydrophilic core space, while the low DS value (< ca. 20 mol-%) led to a destabilization as a unimolecular nanocapsule and a lower encapsulation ability. In particular, 2 with an ca. 23% DS value showed an efficient encapsulation. Based on a release test of the RB-loaded unimolecular nanocapsules, the polymers showed a high RB-holding ability in water.

The ring-opening multibranching polymerizations of 1,6-anhydro-β-d-glucopyranose (1) and 1,6-anhydro-β-d-galactopyranose (2) have been studied in order to synthesize hyperbranched polysaccharides. The solution polymerization in propylene carbonate and the bulk polymerization of 1 and 2 using a thermally induced cationic initiator proceeded through a ring-opening reaction and a proton transfer reaction to afford highly water-soluble polysaccharides, i.e., poly-1 and poly-2, respectively. For the polymers from 1 and 2 with the same polymerization conditions, the M w,SLS and yield of poly-1 were higher than those of poly-2. Here, poly-1 and poly-2 were characterized as hyperbranched polysaccharides consisting of α- and β-linked d-hexopyranosyl and d-hexofuranosyl repeating units, hyperbranched d-glucan and d-galactan, respectively. In addition, poly-1 and poly-2 had ca. 30−40 mol % nonreducing d-hexopyranosyl and d-hexofuranosyl terminal units, and the degree of branching was ca. 0.38 for poly-1 and 0.44−0.60 for poly-2. The respective viscosities of poly-1 and poly-2 in aqueous NaNO3(0.2 mol·L-1) solution were very low with the intrinsic viscosity values of 0.023−0.042 dL·g-1. The steady shear flow of poly-1 in aqueous solution exhibited a Newtonian behavior with steady shear viscosities independent of the shear rate, even at high concentrations. The results indicated that the characteristics of the viscosities were attributed to the spherical structure of the hyperbranched polysaccharide in aqueous solution.

A novel biodegradable unimolecular reversed micelle consisting of a poly(L‐lactide) (PLA) shell and a hyperbranched D‐mannan (HBM) core, that is, a chestnut‐shaped polymer (PLA–HBM), was synthesized by the polymerization of L‐lactide on HBM with 4‐(dimethylamino)pyridine (DMAP) as the catalyst. The obtained polymers were soluble in dimethyl sulfoxide, tetrahydrofuran, and chloroform but insoluble in H2O. The molecular weights of the PLA chain on PLA–HBM tended to increase with increasing polymerization time. The number of PLA chains on PLA–HBM could be controlled by the ratio of DMAP to the sugar unit in HBM. The obtained copolymer, PLA–HBM, acted as a unimolecular reversed micelle with an encapsulation ability toward the hydrophilic molecule. In addition, the entrapped hydrophilic molecules were slowly released from the core of PLA–HBM, and the release rate was accelerated by the breaking of the PLA chains of the shell when proteinase K as a hydrolase of PLA was used. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 406–413, 2006