Synthesis And Self-assembly Behavior Of Poly(ethylene Glycol)-b-poly(ε-caprolactone) With Pedant Carboxyl Groups

Poly(e-caprolactone)(PCL) is one of the important aliphatic polyester materials, which have been widely used in biomedical filed due to its biodegradability, biocompatibility and higher permeablity to drugs. However, the high crystallinity, poor hydrophilicity and lack of functional groups along the PCL backbone have limited its further application. The crystallinity and hydrophilicity of PCL could be improved by introduction of hydrophilic reactive groups. Recently, in the research of the functionalized PCL materials, there are few reports about the water-soluble ionic PCL. The water-soluble polymers based on PCL could self-assemble into micelles in aqueous solution without any organic solvent, and so they are environmental friendly. Therefore, it is significantly important to develop ionic PCL with pendant reactive groups. The purpose of this paper is to introduce carboxyl groups to the PCL through chemical modification and prepare the water-soluble PCL, and the solution properties were further studied.The main contents of this paper are summarized below:1. A series of methoxyl poly(ethylene glycol)-b-poly(ε-caprolactone) bearing pendant carboxyl groups (mPEG-b-P(2-CCL-co-6-CCL)) with different compositions were synthesized by ring-opening polymerization of2/6-(bezyloxycarbonylmethy)-ε-caprolactone, initiated with methoxyl poly(ethylene glycol) using stannous octoate as the catalyst, followed by the catalytic debenzylation in the presence of hydrogen gas. Their structure was confirmed by1H NMR,13C NMR and FTIR. GPC results indicated that the copolymers had a relatively narrow polydispersity. Contact angle test, DSC, WXRD and TG were used to estimate the crystallinity, hydrophilicity and thermal properties of these copolymers.2. Polymeric micelles were prepared by direct pH-induced micellization method. The self-assembly behavior of the copolymers in aqueous solution were determined by Dynamic light scattering, potentiometric titration, fluorescence and transmission electron microscopy measurements. The results demonstrated that the introduction of carboxyl groups endowed the copolymer pH-sensitive properties, and mPEG-b-P(2-CCL-co-6-CCL) copolymers could exist as unimers, micelles or large aggregates in different pH range. Polymeric micelles disaggregated when the solution pH value was above the pKa value of copolymers, and the process was relatively slow.4. Primary disscusion for the preparation of core cross-linking polymeric micelles were progressed according to Dynamic light scattering measurement. The addition of calcium ion or EDDA was propitious to enhance the stability of polymer micelles. However, the research was needed to study further.