Glycoconjugated Polymer. 5. Synthesis and Characterization of a Seven-Arm Star Polystyrene with a β-Cyclodextrin Core Based on TEMPO-Mediated Living Radical Polymerization

β-Cyclodextrin (β-CyD) was modified into a seven-functional initiator ( 1 ) for 2,2,6,6-tetramethylpiperidinyloxy- (TEMPO-) mediated living radical polymerization. Styrene (St) was polymerized with 1 under several conditions to afford original products I − IV . Size exclusion chromatography (SEC) traces of I − IV exhibited trimodal molecular weight distributions; hence, they were fractionated into the respective three species, i.e., main products 2, byproducts 3 with lower molecular weights, and byproducts 4 with higher molecular weights. The weight-average molecular weights determined by SEC and static laser light scattering measurement ( M w,SEC and M w,SLS, respectively) were 1.34 × 10 4 and 2.98 × 10 4 for 2-I, 4.52 × 10 4 and 6.77 × 10 4 for 2-II, 1.35 × 10 5 and 1.87 × 10 5 for 2-III, and 9.67 × 10 5 and 1.89 × 10 6 for 2-IV . The M w,SLS 's were larger than the respective M w,SEC 's. In the 1 H NMR spectra of 2, the signals due to polystyrene (PSt) appeared along with the characteristic signals due to the 1 unit. Therefore, those of 2 were assignable to a star PSt with an acetylated β-CyD core. Polymer 2 was treated with sulfuric acid to give core-cleaved polymer 2 ‘. The M w,SEC 's were 2.80 × 10 3, 9.60 × 10 3, 2.70 × 10 4, and 2.61 × 10 5 for 2 ‘ - I, 2 ‘ -II, 2 ‘ -III, and 2 ‘ -IV, indicating that the arm number of 2, N PSt, was seven. The byproducts 3 and 4 were characterized and found to be a TEMPO-terminated linear PSt and a star−star coupled polymer, respectively. The seven-arm star PSt with a β-CyD core, 5, was obtained through deacetylation of 2 using sodium methoxide in dry THF. The M w,SLS values were 3.96 × 10 5, 3.78 × 10 5, 2.40 × 10 5, and 1.94 × 10 6 for 5-I, 5-II, 5-III, and 5-IV . Hence, 5-I and 5-II showed aggregation in a good solvent for PSt with aggregation-numbers ( N A ) of 13 and 6, respectively.