Preparation And Properties Of Polyimides Optical Materials Based On Thiol-Ene Click Reaction

Polyimide(PI)is highly expected in the field of optoelectronics due to its excellent heat resistance,environmental stability,insulation and excellent mechanical properties.However,the application of traditional polyimide have seriously hindered as optical materials due to poor solubility,low light transmittance,low refractive index,low luminous efficiency and other factors.In this thesis,the effects of various structural designs on the optical properties of PI were discussed on the molecular level.Based on this,starting from the molecular design and synthesis of the monomer,combining with the thiol-ene click chemistry,a series of special structures and functional groups were successfully introduced into polymer backbone,and a variety of PI optical materials with excellent properties were prepared.Three kinds of biscitraconimide(BCI)monomers,4,4'-(diaminodiphenylsulfone)biscitraconimide(DDS-BCI),1,2-(ethylenediamine)biscitraconimide(EDA-BCI)and m-(xylylenediamine)biscitraconimide(MXDA-BCI),were prepared by reflux dehydration in glacial acetic acid based on the reaction between citraconic anhydride and three different chemical structures diamines,respectively.As-prepared products further reacted with4,4'-thiodibenzenethiol(TDBT)and 1,6-hexanedithiol(HDT)to synthesize a series of new transparent thermoplastic polythioetherimides(PTEI)with excellent solubility,high refractive index and low birefringence.All PTEI samples had the 5%weight loss temperatures between332? and 417? and the thermal expansion coefficient ranged from 39.4 to 94.8 ppm/k,showing good thermal stability.Besides,the transmittance of PTEI films at 450 nm exceeded85%,the refractive index(n)measured at 633 nm reached up to 1.6181-1.6582 and in-plane/out of-plane birefringence(?n)values were between 0.0014 and 0.0036.Especially DDS-BCI/TDBT sample exhibited the highest refractive index,relatively smaller birefringence and better thermal stability among all PTEI films,which is expected to be an ideal optical material.Two kinds of soluble polythioetherimides DDS-BCI/DTT(PI₀)and copolymer DDS-BCI/DTT/TDBT(PIs)were prepared from 4,4'-(diaminodiphenylsulfone)biscitraconimide(DDS-BCI),hydroxyl substituted DL-dithiothreitol(DTT)and4,4'-thiodibenzenethiol(TDBT)by thiol-ene click reaction.The hydroxyl groups on the backbone of PIs can provide organic-inorganic bonding sites.By controlling the molar ratio of titanium/zirconium n-butoxide to PIs,two series of polythioetherimides nano hybrid films(PIs-Ti-X%and PIs-Zr-X%)with inorganic content of 4-12 wt%were prepared.SEM and XRD analysis results showed that nano-hybrid films with good dispersion were formed.The5%thermal decomposition temperature(T_d5)of PIs-Ti-X%and PIs-Zr-X%hybrid films can reach 342? and 331?,respectively,and the glass transition temperatures were between189-225? and 184-229?.The thermal expansion coefficients were as low as 43.2 ppm/K and 38.8 ppm/K,indicating that two types of hybrid films had good thermal stability and dimensional stability.In addition,they had tunable refractive indices at 1.6920-1.7341 and1.6867-1.7247,respectively.The optical transparency at 450 nm were higher than 75%and89%,indicating their potential optical applications.Alkenyl-terminated polythioetherimides(PIs)were designed and synthesized using a thiol-ene click reaction.Further,double bond-terminated PIs were modified by thiol-ene reaction to obtain carboxyl and ester-modified polymer ligands(PIs-NL and PIs-ME),respectively.Finally,PIs-NL and PIs-ME were coordinated with Europium ion(Eu(?))and Terbium ion(Tb(?))to obtain four series of luminescent polymer-rare earth complexes,namely PIs-NL-Eu and PIs-NL-Tb,PIs-ME-Eu and PIs-ME-Tb.All the complexes had good solubility and thermal stability,and their photoluminescence properties and the relationship between their structure and luminescence had been studied in depth.The results showed that the bonded terminal carbonyl group can effectively sensitize the fluorescence emission of Eu(?)and Tb(?).PIs-NL-Eu and PIs-ME-Eu produced red luminescence at the excitation wavelength of 385 nm,while the complexes of the two series of PIs-NL-Tb and PIs-ME-Tb showed strong green luminescence under 365 nm light.In addition,the fluorescence intensity of several complexes could be adjusted by changing the excitation wavelength.