Fabrication And Application Of UV-Responsive Polymeric Assemblies

Stimuli-responsive polymers refer to a type of polymers whose physical or chemical properties will change under specifi c external stimuli.By slowly adding water,amphiphilic stimuli-responsive polymers can be assembled into various nanostructures,such as micelles,vesicles,etc.The morphology and chemical structure of the aggregates will change under the action of corresponding external stimuli.These characteristics make them widely used in drug release,tissue engineering,and selfdegradable materials and other fields.This thesis mainly studies the self-degradation process of amphiphilic stimuli-responsive polymers,the construction of polymer vesicles,and the controlled release of drugs.The dissertation mainly includes the following two parts:1.A series of precise sequence stimuli-responsive oligomers were designed and synthesized using citronellol-modified o-nitrobenzyl alcohol as the trigger moiety;and then,through the efficient reaction between isocyanate and hydroxyl groups,the stimuli-responsive oligomers were blocked with the hydrophilic molecule Tag to obtain the amphiphilic precise sequence stimuli-response polymers,Trigger-M-Tag and Trigger-MM-Tag,which can self-assemble into nano-spherical micellar assemblies by slowly adding water using 1,4-dioxane as a co-solvent.The degradation process of the Trigger-MM-Tag polymer and the corresponding self-assemblies were investigated by means of GPC,DLS and TEM.It was found that when being exposed to 365 nm UV irradiation,the o-nitrobenzyl ester linkages at the chain ends can be photo-cleavaged,the decaged primary amine groups then underwent a domino-like degradation via 1,6electron rearrangement elimination,thus causing the degradation of the polymer and the dissociation of the micellar structure,as well as the release of model drug molecule Nile Red from the hydrophobic micellar cores.Therefore,the controlled release of the drugs by means of light irradiation can be fulfilled.2.The amphiphilic photo-responsive diblock copolymers,PEG45-b-IM12,PEG45-bIM21 and PEG45-b-IM34,were prepared by the RAFT polymerization of photoresponsive monomer Trigger-IM in the presence of macromolecular chain transfer agent PEG45-CTA method.These polymers can self-assemble into worm-like micelles,vesicles and large composite micelles respectively by slow adding water into the solution.Then focusing on the photo-reactive behavior and the drug release process of vesicles,the polymer vesicles were irradiated with 365 nm ultraviolet light,resulting in the photolysis of the o-nitrobenzyl ester linkages in the side chains of the hydrophobic blocks.The decaged primary amine groups then underwent amidation reaction with the ester bonds in the side chains of the adjacent polymers,thus causing "traceless crosslinking" within the vesicular bilayers to maintain the structural stability.At the same time,the hydrophilicity and permeability of the vesicular bilayers would be enhanced because of the protonation of the unreacted primary amine groups,which greatly promoted the release of hydrophobic drug Nile red and hydrophilic drug doxorubicin hydrochloride loaded in the vesicular bilayer and the lumen respectively.Therefore,the polymer vesicles have potential applications in the fields of drug carriers,nanoreactors and other fields.