Preparation And Photo-responsive Properties Of Azopyridine Polymer Vesicles

Amphiphilic block copolymer aggregates, like small-molecule surfactants, can assume a range of different morphologies in dilute solution, including spheres, rods, vesicles, compound micelles, and others. In the past years, vesicles prepared from the block copolymers have been well investigated. The interest in polymer vesicles was motivated, in part, by their potential use as microreactors, targeted drug delivery, contrast enhanced imaging, and mimic for biological membranes. Special groups were connected to the polymer to prepare stimuli-responsive polymer vesicles.Recently, amphiphilic azobenzene-containing amphiphilic polymers have received considerable attention. Upon light irradiation, azo polymers can show a variety of structure and property variations triggered by the trans-cis photoisomerization of the azo chromophores, which in turn triggers mesoscopic up to macroscopic changes, such as photomechanical effect and a conversion from light to mechanical energy.In this thesis, azobenzene-containing amphiphilic diblock copolymers, poly(N-isopropylacrylamide)-b-poly{6-[4-(4-pyridyazo) phenoxy] hexylacrylate} (PNIPAM-b-PAzPy) was synthesized by reversible addition-fragmentation transfer (RAFT) polymerization; The achieved diblock copolymers were characterized by NMR, GPC, UV-vis spectroscopy and DSC measurement; The prepared polymer vesicle was confirmed by TEM, CLSM measurement. Self-assembly and photoresponsive behaviors of the amphiphilic azo copolymers were investigated. They are described as below:1. Amphiphilic diblock copolymers PNIPAM-b-PAzPy was synthesized by RAFT polymerization of NIP AM and AzPy monomers. In H2O/THF mixture, amphiphilic PNIPAM-b-PAzPy self-assembles into giant spherical micro-vesicles, which were dispersed in the mixture. Using optical microscopy, the vesicle was observed reversible swelling-shrinking deformation under the alternate UV light at 365nm and visible light at 436nm. The degree of the swelling could be controlled by the power of the UV light. UV-vis spectra demonstrated that the isomerization of azo units resulted in the reversible deformation. In addition, under the UV light, the real-time fusion process of vesicles is presented and the derivation is preliminarily due to the perturbation by photoinduced trans-to-cis isomerization of azobenzene units in the vesicles.2. Based on the photo-responsive property of the vesicles self-assembled from PNIPAM-b-PAzPy, we designed a cross-linking reaction between 1, 3-dibromopropane and PAzPy in the vesicles to investigate relationship between such a structure and the reversible swelling-shrinking deformation. The cross-linked vesicles were successfully prepared. In the irradiation experiment, the photo-induced swelling was found to be decrease along with the cross-linked extent of the vesicles. As revealed by UV-vis spectra, the photoisomerization of azo units was inhibited by the cross-linking, which lowered the degree of swelling. On the other hand, cross-linking also restrain the fusion of the vesicles so that partly fusion occurred when the vesicles were cross-linked much.