Synthesis, Properties And Application Of PCL-Based Block Copolymers Via The Combination Of Controlled/Living Radical Polymerization And Ring-Opening Polymerization

Controlled/living radical polymerization (CRP) has become a hot topic in the polymer chemistry due to mild reaction condition, extensive select of monomers and good control of molecular weight. Moreover, the well-defined polymers, such as block, graft, random, branched and hyperbranched polymers could be readily prepared by combining with other polymerization methods. Poly(e-caprolactone) (PCL) were wildly applied in medical and packing industry owning to excellent biodegradability and biocompatibility. In this paper, block polymers containing PCL segment were prepared by the combination of nitroxide-mediated radical polymerization (NMP) or atom transfer radical polymerization (ATRP) and ring-opening polymerization of?-caprolactone (?-CL). and then the properties and application of the obtained copolymers were studied. The main research contents and results were listed as follows:1. Poly(e-caprolactone)-block-polystyrene(PCL-b-PSt) was synthesized via a combination of nitroxide-mediated radical polymerization of styrene (St) and ring-opening polymerization of?-CL through two-step and one-step polymerization, respectively. The copolymer was characterized by hdrogen nuclear magnetic resonance spectroscopy ('H NMR), fourier transform infrared spectroscopy (FTIR), electric paramagnanetic resonance(EPR), gel permeation chromatography (GPC) and thermgravimetry analysis (TGA). It was demonstrated that in the two-step polymerization, the mechanism of polymerization of St fulfilled a typical well-controlled polymerization. While in one-step polymerization, the chain propagation of?-CL was faster than that of St, according to the result of the polymerization time and the feed ratio of St to?-CL. The TGA analysis showed the thermal stability of PCL-b-PSt copolymer was better than that of PCL homopolymer.2. Poly(?-caprolactone)-block-Poly(N-vinyl pyrrolidione) (PCL-b-PNVP) copolymer was prepared through nitroxide-mediated radical polymerization of NVP in the presence of PCL with terminated-nitroxide radical group (PCL-T), prepared by the ring-opening polymerization of?-CL with 4-hydroxyl-2,2,6,6-teramethylpiperidinyl-1-oxy (HTEMPO) as initiator.1H NMR, FTIR and GPC were applied to character the structure of the copolymers. The self-assembly behavior of the copolymers in the aqueous media was studied by fluorescence spectra, dynamic lighting scanning (DLS) and transmission electron microscope (TEM). The results illustrated that PCL-b-PNVP could be self-assemblied into well-dispersed spherical micelles with a lower critical micelle concentration (CMC) than surfactant. The cytotoxicity assay showed that the PCL-b-PNVP has relatively higher cell viability with the phosphate buffer solution (PBS) as a control.3. Poly(?-caprolactone)-block-Poly(N-isopropylacrylamide)(PCL-b-PNIPAAm) was obtained using azobisisobutyronitrile (AIBN) as initiator and N-isopropylacrylamide (NIPAAm) as monomer in the presence of PCL-T.'H NMR, FTIR and GPC were used to confirm the polymer structure and the influencing factors of the polymerization were also investigated in detail. The results showed that the molar ratio of PCL-T to AIBN, molecular weight of PCL-T and polymerization temperature had extensive influence on the composition, molecular weight and molecular weight distribution of PCL-b-PNIPAAm copolymer. The obtained copolymer could be self-assembled into spherical micelles with PCL as core and PNIPAAm as shell in aqueous solution, and the lower critical solubility temperature(LCST) of the copolymer was lower than that of PNIPAAm homopolymer.4. A novel amphiphilic temperature-responsive PCL-b-P(NIPAAm-co-NVP) copolymer was synthesized by copolymerization of NVP and NIPAAm in the presence of PCL-T. 1H NMR, FTIR and GPC were used to characterize the the structure of the copolymer. The self-assembly behavior and thermo-responsiveness of the copolymer were analyzed by fluorescence spectra, ultraviolet spectra. DLS and TEM. The results demonstrated that the copolymer could be self-assembled into core-shell micelles, and the LCST of copolymer is higher than that of PNIPAAm homopolymer. The cytotoxicity assay in vitro showed that the relative viability of cell in the copolymer micelle solution is almost same as in the phosphate buffer solution. The drug release behavior of DOX-loaded polymer micelle in vitro exhibited the discrepancy at different temperature.5. One novel poly(?-caprolactone)-block-poly(methoxymethyl acrylate) (PCL-b-PMOMA) copolymer was synthesized by a combination of ring opening polymerization (ROP) of?-caprolactone (?-CL) and atom transfer radical polymerization (ATRP) of methoxymethyl acrylate(MOMA). After that the pH-responsive amphiphilic poly(e-caprolactone)-block-poly(acrylic acid) (PCL-b-PAA) was prepared through the mild selective hydrolysis in the mild conditions. The result showed that hemiketal ester of acrylic acid is an excellent derivative of acrylic acid to prepare copolymer containing PAA segment, and the formed PCL-b-PAA micelle showed highly sensitive to pH and ionic strength in aqueous solution. The biomineralization assay indicated that the crystallization process of CaCO3 over PCL-b-PAA micelle solution was affected by the concentration of the copolymer micelle solution and the metastable vaterite could be obtained.