Light Response Preparation And Properties Of The Polymer Vesicles

Amphiphilic block copolymers can self-assemble to form colloidal size aggregates or micelles. 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 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. Moreover, polymer vesicles are versatile structures that can be prepared in different sizes (from nanometer to micrometer) and in different media including aqueous, organic, and aqueous-organic mixtures. Size of the vesicles can be controlled by the components of the blocks and their ratio in the copolymers. On the other hand, vesicle size is also sensitive to the composition of the co-solvent, the temperature, the pH and the ionic strength.In solutions of amphiphilic molecules or polymers containing suitable ehromophores, exposure to light can be used to achieve photoresponses, such as precipitation, aggregation, and self-assembly. Recently, 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.In this thesis, azobenzene-containing amphiphilic diblock copolymers, poly(N-isopropylacrylamide)-b-poly{6-[4-(4-methylphenyl-azo) phenoxy] hexylacrylate} (PNIPAM-b-PAzoM) and poly(acrylic acid)-b-poly{6-[4-(4-methylphenyl-azo) phenoxy] hexylacrylate} (PAA-b-PAzoM), were synthesized by successive reversible addition-fragmentation transfer (RAFT) polymerization; The achieved diblock copolymers were characterized by NMR, GPC, UV-vis spectroscopy and DSC measurement; Self-assembly and photoresponsive behaviors of the amphiphilic azo copolymers were investigated; In addition, properties of elastic behavior of the azo vesicular membranes and the luminescence of Eu(DBM)3Phen in the membranes were discussed. They are described as below: 1. Amphiphilic diblock copolymers PAA-b-PAzoM were synthesized by successive reversible addition-fragmentation transfer (RAFT) polymerization of AA and AzoM monomers. In H₂O/THF mixture, amphiphilic PAA-b-PAzoM self-assembles into giant spherical micro-vesicles, which were dispersed in the mixture. Using UV-vis spectroscopy and optical microscopy, it is demonstrated that the spherical shape of the vesicles results from a framework composed of the azobenzene H-aggregate skeleton. A plausible structural model of the micro-vesicles is proposed, and a discussion on the formation of H-aggregates and the deformation of the azo micro-vesicles induced by 365 nm and 436 nm light irradiation is presented.2. Amphiphilic diblock copolymer PNIPAM-b-PAzoM was synthesized by successive reversible addition-fragmentation transfer (RAFT) polymerization of NIPAM and AzoM monomers. In H₂O/THF mixture, amphiphilic PNIPAM-b-PAzoM self-assembles into giant micro-vesicles. Upon irradiation of light at 365 nm, fusion of the vesicles was observed directly under an optical microscope. The real-time fusion process is presented and the derivation is preliminarily due to the perturbation by photoinduced trans-to-cis isomerization of azobenzene units in the vesicles.3. Elastic Character of the sefl-assembled azo vesicular membrane was investigated by using the optical tweezers technique. A recoverable elastic deformation of the vesicular cluster was induced by the trapping force derived from 810 nm laser. During the deformation process, optical trapping force of pN magnitude increased linearly with increment of the displacement of the suspended particle.4. Rare-Earth chelate, Eu(DBM)₃Phen, was introduced to the azo vesicles system by self-assembly of amphiphilic PNIPAM-b-PAzoM in H₂O/THF mixture. Luminescent polymer vesicles are presented due to the photoinduced luminescence of Eu(DBM)₃ Phen. The luminescent intensity of Eu(DBM)₃Phen embedded in the azo polymer vesicular membrane can be modulated by irradiation of UV and visible light, which was in-situ traced by fluorescence microscopy.