Structural Design And Performance Study Of Spiropyran-based Polymeric Micelles

In recent years,intelligent materials have been widely used in various industries because of their ability to change their properties through stimulation by the external environment.Light has the advantages of being remotely controllable,wavelength and energy controllable,non-invasive,and non-destructive compared with other stimulating factors.Spiropyran and its derivatives are typical photoresponsive molecules with two isomers with different properties under different light conditions,namely the planar open-loop state（MC）and the three-dimensional closed-loop state（SP）,and the isomers are reversible.It was shown that the spiropyran molecule was in the hydrophobic closed-loop SP state under the visible（Vis）light and the hydrophilic open-loop MC state under the irradiation of ultraviolet（UV）light.The introduction of spiropyran and its derivatives into polymers to develop photoresponsive polymeric materials has received significant attention in recent years.Existing studies have generally focused on photoresponsive polymer recycling and color change.The morphology and catalytic properties of photo-modulated polymer-based nanoparticles still need to be sufficiently investigated.In this thesis,we developed a kind of polymer-based nanomicelles with spiropyran block as an intermediate layer by taking advantage of the photoresponsive properties of spiropyran,and the size of the hydrophobic nuclei of the nanomicelles changed with the change of light conditions.The effect of the hydrophobic nuclei’s size on dyes’adsorption and the"concentration effect"in the catalytic reaction was investigated using the nanomicelles as a carrier.In addition,we designed a tunable light-and heat-responsive nanomicelle.We investigated the performance of the release of coumarin 102 under different stimulation conditions.The details are as follows:（1）A tri-block polymer P(OEGMA₅₁-b-SPA₁₀-b-MMA₁₄)-NHS（1）with nitro-spiropyran as an intermediate block was prepared by reversible addition-break chain transfer polymerization（RAFT）by introducing hydrophobic monomer methyl methacrylate（MMA）,photosensitive monomer spiropyran（SPA）,and hydrophilic monomer poly（ethylene glycol）methyl methacrylate（OEGMA）.The photoresponsive nanomicelles M1 were obtained by self-assembly of polymer 1in water.The closed 3D spiropyran（SP）morphology and the open planar anthocyanine（MC）morphology will transformed under different light irradiation,accompanying with hydrophobic and hydrophilic transitions and reversible size changes of the hydrophobic core of the micelles.transmission electron microscopy（TEM）and dynamic light scattering（DLS）analysis verified the size change.This result was also confirmed in the methyl red adsorption experiments.Under visible light,the micelles have a strong dye adsorption capacity with a 97.9%adsorption rate.Under UV irradiation,the nucleation diameter of micelles decreased,and the dye adsorption rate decreased to 66%.In addition,we prepared the polymer P(OEGMA₅₁-b-SPA₁₀-b-MMA₁₄)-TREN（2）by post-polymerization modification method through the reserved NHS-activated ester sites.Ethyl cyanoacetate and p-tolyl aldehyde were selected as reaction substrates,and polymer 2 was self-assembled in water to form a catalytic nanoreactor M2 catalyzing the classical Knoevenagel condensation reaction.GC-MS detected the catalytic reaction.Under UV and visible light irradiation,there were increasing trends of yields in both cases.In the MC state,the hydrophobic nuclei became smaller,the local concentration of the catalyst became higher correspondingly,which made the catalytic reaction rate became higher.This strategy is expected to provide an idea for the"programmed catalysis".（2）The development of drug-release carriers usually uses hydrophobic dyes as drug models.In this thesis,the release performance of nanomicelles was investigated using the hydrophobic fluorescent dye coumarin 102 as a model.The carbamate-containing spiropyran molecule（SPMA）is more conducive to stabilizing the micelle structure than the conventional SPA.In this study,N,N-dimethylacetamide（DMA）,the photosensitive monomer SPMA and the temperature-sensitive monomer N-isopropyl acrylamide（NIPAAm）were introduced by RAFT polymerization to prepare the light-and thermo-dual responsive polymer PDMA₅₀-b-(SPMA₂₀-co-NIPAAm₁₇)（1）.Above the LCST and under visible light,polymer 1 self-assembled into nanomicelles with photo-and thermo-bi-responsiveness.The morphology of the nanoparticles was demonstrated to be spherical by TEM and DLS.Keeping other conditions were unchanged,the basic structure of the nanomicelles was relatively stable under the UV light,the permeability in the nucleus was changed due to the changes of hydrogen bonding between the MC states of spiropyran molecules and theπ-πstacking effect,the release rate of coumarin 102 was 51%;At room temperature,the nanomicelles underwent partial disintegration,and the release rate of coumarin 102 was 77%;under the irradiation of UV and at room temperature,the nanomicelles were wholly disintegrated under the dual stimulation,the release rate of coumarin 102 was 96%.In conclusion,we demonstrated a kind of light-and thermo-dual responsive polymer micelle.The micelle can be easily stimulated and regulated providing an new construction strategy for preparing controlled and synergistic release nanoreactors.