Glycoconjugated Polymer. 4. Synthesis and Aggregation Property of Well-Defined End-Functionalized Polystyrene with β-Cyclodextrin

Abstract

2,2,6,6-Tetramethylpiperidinyloxy (TEMPO)-substituted β-cyclodextrin (β-CyD), 1, was synthesized as the initiator for the nitroxide-mediated living radical polymerization. Styrene (St) was polymerized with 1 using a molar ratio of St and 1 in a feed ([St]/[1]) of 200 at 120 °C for 6 h. The size exclusion chromatography (SEC) trace of the product exhibited a symmetrical peak with a weight-average molecular weight (Mw,SEC) of 11 400 and a polydispersity (Mw/Mn) of 1.13. In the 1H NMR spectrum of the product, the signals due to polystyrene (PSt) appeared along with the characteristic signals due to the 1 unit. Thus, the product was assignable to the end-functionalized PSt with acetylated β-CyD, 2. The introduction of acetylated β-CyD into 2 was found to occur in a quantitative fashion, which was confirmed by thin-layer chromatography equipped with a flame ionization detector (TLC-FID). For the [St]/[1] of 600 at 120 °C, the St/1 system proceeded in a controlled manner to afford 2 with polymerization times of 1.5−9 h with yields of 5−40% and Mw,SEC's of 7500−26 000. On the other hand, the St/1 system for 15 and 20 h afforded polymers with 54 and 75% though an unexpected side reaction occurred. Polymer 2 with Mw,SEC's of 7500−26 000 was modified by deacetylation using sodium methoxide in dry THF into end-functionalized PSt with β-CyD, 3. Particle formation was observed during dynamic laser light scattering measurements of 3 in benzene, indicating that 3 was stably suspended in a good solvent for PSt by forming aggregates with β-CyD as a core. The average aggregation numbers (NA) of the aggregates were found to range from 42 to 125, which were determined by static laser light scattering measurement.