Synthesis And Self-assembly Of Thermosensitive Block Polymers

Thermosensitive amphiphilic block polymers can be self-assembled into water-based micelles with hydrophobic groups as the core and hydrophilic groups as the shell,and can respond to changes in solution temperature.Therefore,it is used in fields like drug release,extraction and separation,enzyme immobilization,molecular machinery,tissue engineering and so on.A series of temperature-sensitive block copolymers PNIPAM_b-PMEMO-PNIPAM_b were synthesized by reversible addition-fragmentation chain transfer polymerization?RAFT?,using temperature-sensitive N-isopropylacrylamide?NIPAM?as the hydrophilic monomer,3-methacryloxypropyltrimethoxysilane?MEMO?as the hydrophobic monomer,S,S'-bis??,?'-dimethylacetic acid?trithiocarbonate?TTC?as the chain transfer agent and azobisisobutyronitrile?AIBN?as the initiator.Their structures were characterized by¹H-NMR and GPC.The thermosensitive properties,self-assembly properties and micellar properties of triblock polymers and their applications were studied systematically by UV-spectrophotometry,surface tension measurement and dynamic light scattering?DLS?.1.The thermosensitive properties of PNIPAM_b-PMEMO-PNIPAM_b with different block ratio were studied by UV-spectrophotometry and dynamic light scattering.It was shown that the polymers with different block ratio were temperature-sensitive,and PNIPAM₁₄-PMEMO-PNIPAM₁₄hasthebesttemperature-sensitivity.Temperature-sensitivity of block polymers was reversible.2.The effect of solution pH on the thermo-sensitivity of polymer was studied.The results show that changing the pH value of the solution,the polymer LCST value correspondingly changed and the pH range of polymer was from 5.5 to 8.5.3.The effects of different concentrations of NaCl,CaCl₂ and MgCl₂ on the micellar solution were studied.The results showed that in a certain concentration of NaCl,CaCl₂and MgCl₂ solution,the polymer LCST value did not change significantly,the polymer has good resistance to Cl^-ions.At the same time,it was found that the same anion had the same effect on the thermal sensitivity of the polymer.The presence of cations in the solution had no effect on the thermal sensitivity of the polymer.4.The results show that the polymer has obvious temperature sensitivity in NaBr?KBr solution,its LCST value increases with the increase of Br^-concentration.In Na₂SO₄?K₂SO₄ solution,the polymer has obvious temperature sensitivity.However,the LCST value decreased with the increase of SO₄^2-concentration.5.The results show that the polymer has obvious temperature sensitivity in the Na₂CO₃?K₂CO₃ solution.When the CO₃^2-concentration is lower than 0.10 g/L,the LCST value of the polymer gradually increases.When the CO₃^2-concentration is greater than0.1 g/L,the polymer LCST value gradually decreases.6.Surface tension method was used to study the surface activity of the block polymer PNIPAM_b-PMEMO-PNIPAM_b.The critical micelle concentration?CMC?of the polymer was investigated by measuring the surface tension of the polymer solution.The results show that the polymers with different block ratio have apparent surface activity,and as the PMEMO content in the polymer increases,the polymer CMC value did not change significantly;however,the surface tension of the polymer reaching the CMC with the increase of the MEMO content showed a downward trend first and then increased.7.The micelle properties of the block polymer solution were studied by means of dynamic light scattering.The micelle size is smaller before the polymer reaches the LCST value.With the increase of the content of PMEMO in the polymer,the particle size of the polymer tends to decrease first and then increase.The minimum value of 115.9 nm occurs when the PNIPAM?PMEMO is 28?1.After the polymer reaches the LCST value,the particle size of the micelles rapidly increases.The PDI value of the polymer solution remains below 1.000 indicating good uniformity of stability of the polymer.8.With pyrene as a hydrophobic drug model,the solubilization of the polymer was studied.The results show that the block copolymer micelles have some solubilities to hydrophobic drugs.