• Polymer(Korea)
• /
• v.30 no.1
• /
• pp.28-34
• /
• 2006

A series of methoxypoly(ethylene glycol) $(MPEG)-poly(\varepsilon-co-L-lactide)$ (PCLA) diblock copolymers were synthesized by ring-opening polymerization of a mixture of $\varepsilon-caprolactone$ and L-lactide with different ratios in the presence of $Sn(Oct)_2$. The characterization of MPEG-PCLA diblock copolymers were examined by $^1H-NMR$, GPC, DSC, and XRD. Kinetic study on ring-opening polymerization of monomer mixtures was carried out in various conditions such as a variation with polymerization time, amount of catalyst, and temperature. The highest conversion obtained in 1.2 ratic of initiator venn catalyst at $110\;^{\circ}C$. The biodegradable characterization of MPEG-PCLA diblock copolymers in aqueous solution was carried out by using GPC for $1\~14$ weeks. The biodegradability of MPEG-PCLA diblock copolymers increased as the L-lactide content of diblock copolymers increased. In conclusion, we confirmed the dependence of polymerization rate according to various conditions. In addition, we can control the biodegradability of MPEC-PCLA diblock copolymers by changing the ratio of PCL and PLA block segment.

• Macromolecular Research
• /
• v.13 no.4
• /
• pp.344-351
• /
• 2005

pH-sensitive block copolymers were synthesized by coupling reaction of sulfamethazine and amphiphilic diblock copolymer, and their micellization-demicellization behavior was investigated. Sulfamethazine (SM), a derivative of sulfonamide, was introduced as a pH responsive moiety while methoxy poly(ethylene glycol)poly(D,L-lactide) (MPEG-PDLLA) and methoxy poly(ethylene glycol)-poly($D,L-lactide-co-{\varepsilon}-caprolactone$) (MPEG-PCLA) were used as biodegradable amphiphilic diblock copolymers. After the sulfamethazine was carboxylated by the reaction with succinic anhydride, the diblock copolymer was conjugated with sulfamethazine by coupling reaction in the presence of DCC. The critical micelle concentration (CMC) and mean diameter of the micelles were examined at various pH conditions through fluorescence spectroscopy, dynamic light scattering and transmission electron microscopy. For MPEG-PDLLA-SM and MPEG-PCLA-SM solutions, the pH-dependent micellization-demicellization was achieved within a narrow pH band, which was not observed in the MPEG-PDLLA and MPEG-PCLA solutions. The micelle showed a spherical morphology and had a very narrow size distribution. This pH-sensitive block copolymer shows potential as a site-targeted drug carrier.

• Macromolecular Research
• /
• v.13 no.4
• /
• pp.352-355
• /
• 2005

• Macromolecular Research
• /
• v.13 no.5
• /
• pp.373-384
• /
• 2005

Novel pH-sensitive moieties containing an s-triazine ring were synthesized with sulfonamide and secondary amino groups. The synthesized pH-sensitive moieties were used for the synthesis of a pH-sensitive amphiphilic ABA triblock copolymer. The pH-sensitive triblock copolymer was composed of diblock copolymers, methoxy poly(ethylene glycol)-poly ($\varepsilon$-caprolactone-co-D,L-lactide) (MPEG-PCLA), and pH-sensitive moiety. These copolymers could be dissolved molecularly in both acidic and basic aqueous media at room temperature due to secondary amino and sulfonamide groups. The synthesized s-triazine rings containing pH-sensitive compounds were characterized by ${^1}H-NMR,\;{^13}C-NMR$, and LC/MSD spectral data. The synthesized diblock and triblock copolymers were also characterized by ${^1}H-NMR$ and GPC analyses. The critical micelle concentrations at various pH conditions were determined by fluorescence technique using pyrene as a probe. Furthermore, the micellization and demicellization study of the triblock copolymer was done with pH-sensitive groups. The sensitivity towards pH change was further established by acid-base titration.