New Biodegradable Amphiphilic Block Copolymers of ε‐Caprolactone and δ‐Valerolactone Catalyzed by Novel Aluminum Metal Complexes

Abstract

Summary: In our previous study [J. Yang, L. Jia, L. Yin, J. Yu, Z. Shi, Q. Fang, A. Cao, Macromol. Biosci. 2004, 4, 1092.], new biodegradable copolymers of diblock methoxy poly(ethylene glycol)-block-poly(ε-caprolactone) and methoxy poly(ethylene glycol)-block-poly(δ-valerolactone), and triblock poly(ε-caprolactone)-block-poly(ethylene glycol)-block-poly(ε-caprolactone) and poly(δ-valerolactone)-block-poly(ethylene glycol)-block-poly(δ-valero-lactone) bearing narrow molecular weight distributions and well-defined block architectures were reported to be prepared with our original aluminum metal complex templates. This work will continue to report new investigations on their water solubility, and reversible thermal responsive micellization and solution to gel transition in distilled water. Among the new synthesized copolymers (P1–P23), seven diblock or triblock samples (P3, P6, P7, P11, P12, P19, and P21) with higher hydrophilic building block populations were revealed to be water soluble under ambient temperature. By means of UV spectrophotometer attached with a thermostat, important parameters as critical micellization mass concentrations (CMCs) and critical micellization temperatures (CMTs) were characterized for these new amphiphile dilute aqueous solution with the aid of an lipophilic organic dye probe of 1,6-diphenyl-1,3,5-hexatriene (DPH). Furthermore, the critical gelation temperatures (CGTs) were simultaneously investigated for these water-soluble block copolymers via a tube tilting method. It was found that the CMC, CMT, and CGT were strongly affected by the population and nature of the hydrophobic building blocks, and a higher hydrophobicity of the new amphiphilic block copolymer finally led to lower CMC and CMT, and higher CGT. In addition, the salts of KBr and NaCl were found to play as a salt-out effect on the solution to gel transition for the diblock P6 and triblock P11, exhibiting an interesting tunable gelation temperature close to 35–42 °C. These results will pave new possibility for the synthesized block structural amphiphiles as potential biomaterials to be applied in vivo. Thermal responsive micellization and gelation of diblock MPEG-b-PCL/PVL and triblock PVL/PCL-b-PEG-b-PCL/PVL.