Synthesis And Addition Polymerization Of Norbornene Derivative With A Pendent Azobenzene Functional Group

The vinyl addition polymers of norbornene which exhibit high Tg (300℃-370℃), good optical properties, low birefringence and low moisture absorption are good optical materials. We should achieve functional polynorbornenes in order to improve the disadvantages of poor solubility in organic solvent, poor adhesion for silicon, metal, poor machinability due to its bis-cyclic structure. One method is the copolymerization,of norbornene with a-olefins. Experiments showed that these polynorbornene exhibit good solubility and high transparency. The second is introducing functional groups. These groups enhanced certain aspect property of polynorbornene, such as adhesion, elongation at break, thermal decomposition temperature, molecular flexibility, solubility, processability.In this study, we demonstrated the synthesis of norbornene monomer functionalized with azobenzene chromophore and its successful vinyl-addition polymerization catalyzed with bis-(β-ketonaphthylamino)nickel(II)/B(C6F5)3 in toluene. The chemical structures of the polar monomer and polymers were confirmed by Fourier Transform Infrared (FTIR) and Nuclear Magnetic Resonance (1H NMR, 13C NMR) Spectra. The polar monomer and polymers were also characterized by UV-visible absorption spectra. The results showed that they all had broad optical absorption band in the range of 300-400 nm. GPC results showed that the number-average molecular weight (Mn)s of copolymer and homopolymer are 4.78×104-5.15×104 and 6.5×105-1.28×106, respectively. The achieved polymers showed high thermal stability above 320℃and good solubility in common organic solvents while their Tg were all below 300℃. The solubility of copolymer is better than that of homopolymer in common organic solvents which gives the proof that the introduction of alkyl chain can effecienly improve the solubility and reduce the Tg of polymers.Photochromism, thermochromism and thermal back-isomerization of copolymer and monomer were studied, the results showed that the photochromism and thermochromism rates of copolymer are a little bigger than those of monomer, meanwhile, The rates of thermochromism order of them both are up to 10-2/s which is much larger than that of side-chain liquid crystalline polymers containing azo group at same experimental condition, which indicated that the synthesis of polymers containing azo using polynorbornene as backbone can improve the optical property of them. The thermochromism process of them is similar to that of photochromism, the order of them both is up to 10-1/℃. After being placed in dark at room temperature, the solution of monomer and copolymer which came to stable state occured thermal back-isomerization, but the rates of thermal back-isomerization are much less than those of photochromism and thermochromism. We also learned that the polarity of solvent has influence on the rate of photochromism, the bigger the polarity of solvent is, the larger the rate is.