Preparation And Performance Of Azobenzene-containing Hyperbranched Polyimides

Photoresponsive polymers have received much attention due to the unique characteristics of the light source,such as remote controllability and environmental protection.Photoresponsive azobenzene-containg polymer materials are one of the most studied photoresponsive polymer.The geometrical changes caused by the cis-trans isomerization of the azobenzene groups in the azobenzene-containing polymers could be applied to the preparation of photodeformable materials.At present,research on photodeformation materials based on azobenzene-containing polymers mainly focuses on azobenzene liquid crystal elastomers.Although azobenzene liquid crystal elastomers have been extensively studied,azobenzene liquid elastomers have poor mechanical properties and thermal stability,which limits their fields of application.In recent years,it was found that polyimide acids and polyimides containing azobenzene groups in the main chain backbones could be applied to the preparation of high performance photodeformation materials.As a special engineering plastic,polyimides have excellent thermal stabilities and good mechanical properties.The introduction of the azobenzene groups into the polyimides systems by covalent bonds could impart photoresponsive to the polyimide materials.However,the linear azobenzene-containing polyimides limited the photoisomerization of the azobenzene group due to its rigid main chain structure and molecular chain entanglement.Therefore,photodeformation materials based on the azobenzene-containing hyperbranched polyimide is prepared because the hyperbranched structure has a large free volume.On the other hand,the hyperbranched polyimides have poor film formability and mechanical properties.In this paper,in order to combine the advantages of linear structures and hyperbranched structures,we have synthesized a series of azobenzene-containing hyperbranched polyimides with different length linear structures and different flexible branching structures.We have studied and compared the solubility,thermal properties,photoisomerization behaviors,photodeformation behaviors and mechanical propertiesof azobenzene-containing hyperbranched polyimides.(1)A novel series of azobenzne-containing hyperbranched polyimides with different lengths of linear stuctures were synthesized.The solubility test showed that the prepared azobenzne-containing hyperbranched polyimides had good solubility.The results of TGA test and DSC test showed that all the polymers have high glass transition temperatures and good thermal stabilities.With the length of the linear structures increased,the glass transition temperatures of the polymer increasesd,but the thermal stabilities decreased.The photoisomerization behaviors of the prepared polymers were studied.The results showed that the photoinduced isomerization rate decreased with the increase of the linear length.The results of photodeformation behaviors of the prepared polymers showed that the films of the prepared polymers have photodeformation properties,and the photodeformation rate decreased with the increase of the linear length.Mechanical properties studies showed that the tensile properties increased correspondingly with the length of the line increased.(2)A novel series of azobenzne-containing hyperbranched polyimides with different flexibilities of branched stuctures were synthesized.The solubility test shows that the prepared polymers had good solubility.The results of TGA test and DSC test show that all of the polymers have high glass transition temperatures and good thermal stability.With the flexibility of branched stuctures increased,both of the glass transition temperatures and the thermal stabilities decreased accordingly.The results of the photoisomerization behaviors of the prepared polymers showed that the photoinduced isomerization rates increased with the increase of the flexibilities of branched stuctures.The results of photodeformation behaviors showed that the films of the prepared polymers had photodeformation properties,and the photodeformation rates increased with the increase of the flexibilities of branched stuctures.With the increase of the flexibilities of branched stuctures,tensile modulus and tensile strength of the polymers decreased,but the elongation at break of the polymers increased accordingly.