Preparation And Properties Of PES Based Flexible White Fluorescent Copolyester

In recent years,white fluorescent polymer materials have shined in the fields of solid-state light sources and holographic display backlights.Compared with traditional small molecule systems,polymer white light materials have the advantages of simple process,low cost,and easy large-area manufacturing.At present,the commonly used method for obtaining polymer white light materials is to dope different chromophores together by blending.This method is simple to operate,but the blend has the disadvantage of phase separation,which will cause the fluorescence color to change.Therefore,in order to solve the problem of unstable material properties caused by blending,it is of great significance to design and synthesize copolymerized white fluorescent emission materials.Synthesis and properties of blue fluorescent copolyesters:poly(ethylene succinate-co-1,4-cyclohexanedimethyl succinate)(PESC)and poly(ethylene succinate-co-isosorbide succinate)(PESI)were prepared by melt polycondensation with blue emitting polyethylene succinate(PES)as the basic structure.The solid-state fluorescence test revealed that the copolyesters can emit strong blue fluorescence under excitation at 365 nm,and its fluorescence intensity increased with the increase of the copolymerization ratio of1,4-cyclohexanedimethanol(CHDM)and isosorbide(IS).In addition,IS improved the fluorescence intensity significantly higher than CHDM,and the two series of copolyesters showed obvious excitation wavelength dependence and crystal induction enhancement effect.By changing the excitation wavelength and crystallinity,the fluorescence color and intensity can be effectively controlled.On the other hand,compared with pure PES,the introduction of CHDM and IS units endowed the copolyester with higher glass transition temperature.The increase in the rigidity of the copolyester molecular chain was beneficial to reduce the non-radiative energy loss in the excited state of the sample and improved its fluorescence intensity.Synthesis and properties of orange fluorescent copolyesters:using the method of melt polycondensation,different groups of glycol monomers(eg,ethylene glycol and butylene glycol;ethylene glycol and hexylene glycol;propylene glycol and butylene glycol)were used to copolymerize with dimethyl terephthalate and tetrachloroperylene anhydride to prepare three kinds of orange fluorescent copolyesters including poly(ethylene terephthalate tetrachloroperylene anhydride-co-butylene terephthalate tetrachloroperylene anhydride)(PEBT),poly(thylene terephthalate tetrachloroperylene anhydride-co-hexylene terephthalate tetrachloroperylene anhydride)(PEHT),and poly(butylene terephthalate tetrachloroperylene anhydride-co-trimethylene terephthalate tetrachloroperylene anhydride)(PBTT).Among them,PBTT has poor molecular chain regularity?crystallization ability,and can be dissolved in organic solvents such as CH₂Cl₂.The remaining samples show poor solubility in solvents,which is not conducive to further reaction in solution system.With the initial decomposition temperature higher than 375^oC,the copolyesters all behaved excellent thermal stability and fluorescence properties.The maximum emission wavelength of the sample had a red shift as the copolymerization ratio of tetrachloroperylene anhydride increased.In addition,The UV absorption curve of PBTT copolyester overlapped with the emission curve of PESC(A₁),which met the requirements of donor-acceptor white light emission.Preparation and properties of white fluorescent copolyesters:through chain extension method,the PESC and PBTT were linked together by toluene diisocyanate(TDI)and the copolymerized white fluorescent polymer was successfully prepared by adjusting the ratio of the two blocks.The CIE coordinates of the copolymer PESC-co-PBTT was(0.27,0.33),belonging to the category of cold white light.In addition,the CIE coordinates of copolyesters with different block ratios were distributed on the line connecting the PESC and PBTT CIE coordinates.Different fluorescent colors on this line can be achieved by changing the ratio of the diblocks.By controlling the crystallization temperature to prepare polymers with different crystallinity,the fluorescent color of the product can be fine-tuned within a certain range.Degradation experiment revealed that the copolyester after chain extension had good degradation performance,and the weight loss was 82.9%in 10 days in Na OH solution.