Synthesis of Hyperbranched Carbohydrate Polymer by Ring-Opening Multibranching Polymerization of 1,4-Anhydroerythritol and 1,4-Anhydro-l-threitol

1,4-Anhydroerythritol (1a) and 1,4-anhydro-l-threitol (1b) were polymerized using trifluoromethanesulfonic acid (CF₃SO₃H) or fluorosulfonic acid (FSO₃H) as a cationic initiator. The polymerizations of 1a and 1b proceeded through a ring-opening reaction with a proton-transfer reaction to produce hyperbranched carbohydrate polymers (2a and 2b) mainly consisting of erythritol and l-threitol units, respectively. The degrees of branching (DB) estimated by the ¹³C NMR spectra of 2a and 2b were ca. 0.28−0.47. The weight-average molecular weight (M_w,SLS) values (3.2 × 10⁴−5.1 × 10⁵) estimated using static laser light scattering (SLS) of the resulting hyperbranched carbohydrate polymers were significantly higher than the weight-average molecular weight (M_w,SEC) values (1.5 × 10³−1.4 × 10⁴) estimated using size exclusion chromatography (SEC). The solution viscosities of 2a and 2b were very low, and the intrinsic viscosities ([η]) of 2a and 2b were in the range from 3.26 × 10^-2 to 7.30 × 10^-2 dL·g^-1. The three-dimensional properties characterized by the SLS and viscosity measurements indicated that 2a and 2b should be nanoscale particles.