Synthesis And Properties Of Polyimides Containing Stereoisomerism Cycloaliphatic Moieties

Polyimide is a kind of polymer with imide group as its characteristic structure.Polyimides have outstanding thermal stability,excellent mechanical strength,extensive chemical stability and relatively low dielectronic constant.However,traditional aromatic polyimides（such as Kapton）often possess the disadvantages of inherent reddish-yellow coloration and insolubility,which decreases their processability and limits their applications in some fields.Therefore,it is urgent to design and develop transparent and soluble polyimides.In this paper,transparent and soluble polyimides were prepared by introducing stereoisomeric alicyclic fragments in the backbone of polyimides.There have been a lot of papers about the structure-properties relationships of polyimides,but there were few papers about the stereoisomerism structure-properties relationships of polyimides.Therefore,this paper also explored the stereoisomerism structure-properties relationships of polyimides in detail,which provided basic data for the selection of stereoisomerism structure in the future.The optical activity of polyimides containing isosorbide and 1,4;3,6-dianhydrocyclohexitol fragments was reported for the first time,which provided reference for the application of optical rotation polyimides.The main research contents were as follows:（1）Diamine isomers（E,A-HBPDA and E,E-HBPDA）containing conformational isomer structure of HBPA were prepared.A series of copolyimides were prepared from diamine monomers with different percentages of diamine E,A-HBPDA and 4,4’-（hexafluoroisopropylidene）diphthalic anhydride（6FDA）.All the copolyimide materials had good thermal properties.The T_g of copolyimide gradually decreased with the increase of E,A-HBPDA content,which was attributed to the fact that twisted conformation of E,A-HBPDA possessing larger free volume than E,E-HBPDA would weaken inter-chain interaction,and loosen chain packing.All polyimides had excellent solubility and excellent mechanical strength.It exhibited good transmittance of 73%-77%at 450 nm.The mechanical properties and transmittance had no obvious regular changes with the change of E,A-HBPDA content.（2）Diamine monomers containing isosorbide or 1,4;3,6-dianhydrocyclohexitol configuration moiety were prepared respectively via nucleophilic substitution reaction and reduction using isosorbide,1,4;3,6-dianhydrocyclohexitol and 2-chloro-5-nitrotoluene as raw materials.Polyimides were prepared respectively from diamine monomers with different percentages of g-NH₂ and 6FDA or 1,2,4,5-benzenetetracarboxylic anhydride（PMDA）via a conventional two-step procedure.All polyimides had good thermal properties.The T_g of g-（0-100%）-PMDA gradually increased from 269°C to 286°C with the increase of 1,4;3,6-dianhydrocyclohexitol diamine content.The T_g of g-（0-100%）-6FDA showed similar rules.In addition,the change of T_g of g-（0-100%）-PMDA with the increase of 1,4;3,6-dianhydrocyclohexitol content was more obvious than that of g-（0-100%）-6FDA.Polyimides g-（0-100%）-6FDA were soluble in common organic solvents.All the polyimide films had excellent mechanical strength.The copolyimide films g-100%-6FDA had transmittance of 75～79%at 450 nm.No significant rules on the optical properties and mechanical properties of the copolyimides were found with the change of 1,4;3,6-dianhydrocyclohexitol content.In addition,it was first reported that polyimides and polyamic acids bearing isosorbide and 1,4;3,6-dianhydrocyclohexitol fragments had optical activity.The specific optical rotation of polyamic acids and copolyimides gradually increased with the increasing of1,4;3,6-dianhydrocyclohexitol fragments.