Preparation of methoxy poly (ethyleneglycol)-b-poly (ε-caprolactone-co-L-lactide) and characterization as biodegradable micelles

To compare methoxy poly (ethylene glycol) (MPEG)-b-poly (ε-caprolactone) (M₇C₁₀L₀) and MPEG-b-poly (L-lactide) (M₇C₀L₁₀), we performed block copolymerization of ε-caprolactone (CL) and L-lactide (LA) to synthesize block copolymers composed of MPEG-b-poly (ε-caprolactone-co-L-lactide) (M_xC_yL_z). The obtained M_xC_yL_z, M₇C₁₀L₀, and M₇C₀L₁₀ had molecular weights close to the theoretical values calculated from the CL and/or LA to MPEG molar ratios and exhibited monomodal gel permeation chromatography (GPC) curves. The micellar characterization of M_xC_yL_z block copolymers in an aqueous phase was carried out by using NMR, dynamic light scattering (DLS), and fluorescence techniques. The diameters of micelles, measured by DLS, were 30–370 nm. The critical micelle concentration (CMC) and partition equilibrium constant (K _v) depended on the block lengths and compositions of block copolymers. The degradation of the M_xC_yL_z block copolymers mainly depends on both the length of hydrophilic MPEG segments and the proportion of the CL and LA in the hydrophobic segments present in their structure. We confirmed that M_xC_yL_z block copolymers formed biodegradable micelles suitable for biomedical applications.