Synthesis,Characterization And Properties Of Azobenzene Polyether-ester Multiblock Alternative Copolymers

This thesis mainly focuses on the synthesis and properties of azobenzene cyclic oligoesters(COAZOs).The azobenzene polyether-ester multiblock alternative copolymers were obtained by an in situ cascade polycondensation-coupling ring-opening polymerization(PROP)process.Azobenzene polyether-ester elastic fibers were prepared by melt spinning method,and their mechanical properties and light response characteristics were studied.The mechanical properties of the polyether-ester fibers are influenced by the different ratio of soft to hard segments,and ultra strong and tough azobenzene elastic fibers were obtained with fast light response.Details are listed below:(1)Azobenzene-containing cyclic oligoesters(COAZOs)were synthesized under the optimized “pseudo-high-dilution” conditions.The structure of the cyclic oligoesters was characterized and confirmed by 1H nuclear magnetic resonance(1H NMR)and matrix-assisted laser desorption/ionization time-of-flight mass spectra(MALDI-TOF MS).Differential scanning calorimetry(DSC)results indicated a liquid crystal phase of the cyclic oligoester during heating,while wide-angle X-ray diffraction(WAXD)and polarizing optical microscope(POM)results revealed the phase is smectic.(2)Azobenzene-containing multiblock alternative copolymers(PAZO-b-PTMO-b-PAZO)n with different soft to hard segment weight ratio(1:1,2:1,3:1,with the copolymer name PTMO-b-PAZO-1,PTMO-b-PAZO-2,PTMO-b-PAZO-3,respetively)were successfully synthesized by using PTMO as macroinitiator and COAZOs as monomer.The molecular weights of the copolymers were studied by gel permeation chromatography(GPC),and the polymerization kinetics was revealed to follow the polycondensation-coupling ring-opening polymerization(PROP)process.For three copolymers with similar molecular weights but different soft/rod segment ratio,PTMO-b-PAZO-1-180(38 kg/mol),PTMO-b-PAZO-2-180(37 kg/mol)and PTMO-b-PAZO-3-180(32 kg/mol),TGA results indicate that the azobenzene multiblock alternative copolymers has good thermal stability,with 5% weight loss temperature all above 370 oC,while DSC results indicate PTMO-b-PAZO-1 and PTMO-b-PAZO-2 copolymers are double crystalline polymers.Dynamic mechanical analysis(DMA)test results show that those copolymers are elastomers with a broad rubber platform.The phase structure of these azobenzene multiblock alternating copolymers was studied by small-angle X-ray scattering(SAXS)and transmission electron microscopy(TEM),where microphase separation was found in PTMO-b-PAZO-1 and PTMO-b-PAZO-2 copolymers,but not in PTMO-b-PAZO-3.The stress-strain test indicates these azobenzene multiblock copolymers have excellent elasticity and strength,and the Young's modulus decreases while the elongation at break increases with the increment of PTMO content.In addition,these azobenzene copolymers show a reversible cis-trans photoisomerization,as revealed by the solution UV-vis absorption spectra.(3)The azobenzene-containing elastic fibers were prepared by melt spinning of corresponding(PAZO-b-PTMO-b-PAZO)n copolymers,with uniform diameter around 100 ?m revealed by optical miscoscopy.The mechanical properties of these elastic fibers were tested by monofilament tensile tester.Similarly,the Young's modulus of the fibers decreases and the elongation at break increases with increasing PTMO content.Under the same strain conditions,the corresponding stress decreases with increasing PTMO content.These fibers are show excellent mechanical properties,with the stress at break around 1 GPa,the elongation at break over 1400%,and Young's modulus over 125 MPa.The UV light-response properties of these azobenzene-containing fibers were tested,indicating these are ultra strong and tough optical response elastic fibers.Among them,the shortest response time can achieve 0.24 s,with the maximum power density around 15.7 k J m-3,and the maximum power density of 38.5 W kg-1.The maximum light conversion efficiency is 2.6%.The above performance is much better than previously reported materials used for "artificial muscles",indicating the potential application of these azobenzene-containing copolymers in this field.The control of the bending and shrinking of the elastic fibers in the quartz tube by UV light indicates that this type of azobenzene poly(ether ester)elastic fibers have potential application as a "remote control robot".