Synthesis And Characteristics Of The Polymers Containing Azobenzene Group By RAFT Polymerization

In this thesis, the reversible addition fragmentation chain transfer (RAFT) polymerizations of monomer and the chain transfer agent (CTA) containing azobenzene group were studied. The obtained polymers were characterized by various techniques. The following systems were showed as below:(1) An azobenzene-based dithiocarbamate, 4, 4'-bis [2-(carbazole-N-dithioformatyl) -2-methyl-propionatyl]-azobenzene (CDMPA), was synthesized and used as the CTA for RAFT polymerization of styrene in anisole solution. Well-defined azobenzene-centered and carbazole-end polystyrene (PS) with well-controlled molecular weight (Mn) and narrow molecular weight distributions (Mw/Mn) was obtained. The good agreement between the theoretical molecular weight (Mn,th) and the molecular weight (Mn,NMR) determined by 1H NMR indicated that most of the polymer chains contained an azo-functional center-group and end-capped with the carbazole moieties, which were derived from the RAFT agent. The obtained polystyrene (PS) showed a strong ultraviolet absorption and emitted fluorescence after excited by UV-irradiation in N, N'-dimethyl formamide (DMF) solutions. The PS was used as the macro-RAFT agent to carry out the polymerizations of N-isopropylacrylamide (NIPAAM) and methyl acrylate (MA). Triblock copolymers (PNIPAAM-b-PS-b-PNIPAAM), (PMA-b-PS-b-PMA), and pentablock copolymers (PNIPAAM-b-PMA-b-PS-b-PMA-b-PNIPAAM) were yielded, respectively. These copolymers were characterized by gel permeation chromatographer (GPC), FT-IR spectroscopy and NMR spectroscopy. The self-assembly behaviors of amphiphilic triblock copolymers in aqueous solution were demonstrated by high performance particle sizer (HPPS) and transmission electron microscopy (TEM).(2) A novel optically active monomer, 6-{4-[4-(1-phenyl-1H-tetrazol-5-yloxy) -phenylazo]-phenoxy}-hexyl methacrylate (PTPPHMA) bearing tetrazole and azobenzol moieties, was synthesized and polymerized by reversible addition-fragmentation chain transfer (RAFT) polymerization using 2-cyanoprop-2-yl dithiobenzoate (CPDB) as the RAFT agent and 2, 2'-azobis(isobutyronitrile) (AIBN) as the initiator. Well-defined optically active photochromic poly(6-{4-[4-(1-phenyl-1H-tetrazol-5-yloxy)-phenylazo]- phenoxy}-hexyl methacrylate) (PPTPPHMA) was obtained."Living"/controlled characteristics were observed in the polymerization: well-controlled molecular weights (Mns), narrow molecular weight distributions (Mw/Mn) of the polymers and successful chain-extension of PPTPPHMA with styrene (St) as the second monomer. The photochemical interconversion between trans and cis isomers of PPTPPHMA in N, N′-dimethyl formamide (DMF) solution was explored under irradiation of ultraviolet light. The evolution of the photoinduced birefringence in the thin films of tetrazole-containing azo Polymers was studied and the saturated value on the glass surface spin-coated film was up to 0.1. The polymer system showed almost fully reverible photoinduced birefringence which is ideal for all-optical switching. The surface-relief-gratings (SRGs) were induced on the polymer films by interference of Kr+ laser beams at 413.1 nm with 35 mW·cm-2 intensity, the diffraction efficiencies from SRGs were measured to be in the range of 2.0%-2.5%. The atomic force microscopy (AFM) results showed the gratings produced on the surfaces of the polymer film.