Preparation And Performance Of Polyimides Containing Azobenzene In Side Chain

The azobenzene groups of azobenzene-containing polymers can undergo photoindued isomerization in the molecular structure under excitation light,and show photoinduced deformation in the macroscopic form,realizing the conversion of light energy into mechanical energy.At present,research on photoinduced deformable azobenzne-containing polymers mainly focuses on azobenzne-containing liquid crystal elastomers and azobenzne-containing liquid crystal polymer networks.Although their mechanism and application research in the field of photoinduced deformation has been very rich,they still have the problem of poor thermal stability,which prevents them from being used in high temperature environments.In recent years,the research on the photoinduced deformation of azobenzene-containing polyimides have received much attention because it is helpful to improve the application of azobenzene-containing polymers in high temperature environments.At present,the research on the photoinduced deformation of azobenzene-containing polyimides has been mainly focused on the polyimides containing azobenzene groups in the main chain,but the research on the photoinduced deformation of polyimides containing azobenzene groups in the side chain are still few.Compared with polyimides containing azobenzene groups in the main chain,polyimides containing azobenzene in the side chain have the advantages of various structures and synthesis methods.In this paper,a series of polyimides containing azobenzene groups in side chain were prepared by direct copolymerization and grafting reaction.The thermal properties and the photoresponsive properties of the polymers were investigated.The specific contents are as follows:(1)A diamine compound containing azobenzene groups was synthesized,and a series of polyimides containing azobenzene groups in the side chain was prepared by using it as a monomer.The result of thermal performance study showed that all of the prepared polymers have high glass transition temperatures and well thermal stability.As the content of azobenzene groups in the polymers increased,the thermal stability of the polymers decreased.The polymers were made into film cantilevers to study the photoinduced deformation behavior.The result of photoinduced deformation behavior research showed that with the content of azobenzene groups increased,the photoinduced deformation rate of the polymers increased;with the thickness of the polymer films increased,the photoinduced deformation rate of the polymers decreased;with the flexibility of the main chain increased,the photoinduced deformation rate of the polymers increased;the photoinduced deformation rate of the polymers under unpolarized laser excitation was larger than that under rpolarized laser excitation.(2)Three azobenzene-containing small molecule compounds containing alkyl chains of different lengths were prepared and azobenzene-containing polyimides with with various lengths of flexible spacers in the side chain were prepared by polyimides containing hydroxyl groups in the side chain and the prepared azobenzene-containing small molecule compounds.The result of thermal performance study showed that all of the polymers have high glass transition temperatures and well thermal stability.With the lengths of the flexible spacers in the side chain of the polymers increased,the thermal stability of the polymers decreased.The polymers were made into film cantilevers to study the photoinduced deformation behavior.The result of photoinduced deformation behavior research showed that with the lengths of the flexible spacers in the side chain of the polymers increased,the photoinduced deformation rate of the polymers increased;with the ambient temperature increased,the photoinduced deformation rate of the polymers increased;the photoinduced deformation rate of the polymers under 442 nm laser excitation was larger than that under 532 nm laser excitation.