Strategy BSynthesis of Polyecaprolactone Microspheres Loaded with NNBishydroxyethylisonicotinamide

N,N-Bis(hydroxyethyl)isonicotinamide being equipped with two hydroxyl groups could be used as a chain transfer agent and in effect become incorporated into poly(e-caprolactone) chains forming poly(e-caprolactone)/N,N-bis(poly(e-caprolactone)isonicotinamide microspheres (cf. Scheme 6). Synthesis of poly-(e-caprolactone) microspheres with chemically bound N,N-bis(hydroxyethyl) isonicotinamide was performed similarly to that described in Section IV.B. 1,4-Dioxane/heptane 1:9 (v/v) mixture was used as reaction medium. Monomer, initiator [(CH3)3SiONa], poly(dodecyl acrylate)-g-poly(e-caprolactone), and N,N-bis(hydroxyethyl)isonicotinamide were used in the following concentrations: [e-caprolactone]0 = 3.8 x 10-1 mol/L, [(CH3^SiONa]0 = 1.76 x 10-3 mol/ L, [N,N-bis(hydroxyethyl)isonicotinamide]0 = 4.0 x 10-3 mol/L, [poly(dodecyl

FIG. 27 1H NMR spectrum of poly(l,l-lactide)/omeprasol microspheres in CDCl3. (From Ref. 50.)

SCHEME 6

acrylate)-g-poly(e-caprolactone)] = 1.6 g/L. Polymerization was carried out at room temperature for 20 min. The yield of microspheres was 72%. Drug loading determined from UV spectra of microsopheres dissolved in 1,4-dioxane (cf. Fig. 28) was 0.45 wt %.

It must be noted that higher concentrations of N,N-bis(hydroxyethyl)isonicot-inamide in polymerizing mixture (2.0 x 10-2 mol/L) in polymerizing mixture allowed synthesis of microspheres with drug loading equal 6.4 wt %.

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