Molecular Design,Synthesis And Application Of High Refractive Index Optical Resin

High refractive index optical resin,which has the advantages of lightweight,flexible structure and properties,optical transparency,impact resistance,easy processing,and low cost,is widely used in optical elements and devices such as sensors,detectors,light-emitting diodes,microlens arrays,and optical fibers.Research has manifested that(1)introduction of high sulfur-containing groups and aromatic conjugated structures into polymers and(2)incorporation of high refractive index inorganic nanoparticles with a particle diameter of less than 40 nm,such as TiO2,ZrO2 and ZnS,into polymer materials,can improve their indices of refraction effectively.However,These optical polymer materials with a high index of refraction reported so far show problems such as complex multi-step synthesis of monomers,poorly visible light transmittance,high cost,difficulty in processing and preparing thick bulk polymer materials.In order to solve these obstacles,a series of optical resins with a high refractive index was synthesized successfully by a simple,fast and efficient one-step reaction,and their nanoimprinting properties and application in microlenses were studied.The large-scale commercial use of high refractive index optical resins has been systematically studied.This work provides valuable research results for the development and application of high-performance,lightweight,miniaturized and integrated optical devices.The main research contents and results are as follows:1.4,4-dihydroxydiphenyl sulfide diacrylate(M-1),4,4-dihydroxydi-phenyl sulfone diacrylate(M-2)and 9,9-bis[(4-hydroxyethoxy)phenyl]fluorene diacrylate(M-3)were synthesized by a straightforward and efficient one-step nucleophilic substitution reaction,which reacted 4,4-dihydroxydiphenyl sulfide,4,4-dihydroxydiphenyl sulfone and 9,9-bis[(4-hydroxyethoxy)phenyl]fluorene with acryloyl chloride,respectively.Tris(4-isocyanatophenyl)thiophosphate triacrylate(M-4),2,5-dimercapto-1,3,4-thiadiazole diacrylate(M-5)and 4,4-dimercaptodiphenyl sulfide diacrylate(M-6)were prepared via a one-step nucleophilic addition reaction.These acrylates containing 0.1 wt%of dibenzoyl peroxide(BPO)initiator were melt polymerized to prepare high refractive index acrylate polymers(P-M-1-P-M-6),whose properties were characterized and investigated,containing high sulfur group and aromatic structure in their molecular chain.P-M-1,P-M-2,P-M-3 and P-M-5 showed excellent thermal stability and their thermal degradation temperature(T5)at 5 wt%weight loss were 386.6?,366.8?,309.2? and 402.3?,respectively.Besides,all the acrylate polymers exhibited excellently optical transparency with the transmittance exceeded 90%at the visible range.Moreover,the refractive indices(550 nm)of P-M-1,P-M-3,P-M-5 and P-M-6 were higher than 1.60,which were 1.6072,1.6268,1.6129 and 1.6363,respectively,indicating that the introduction of a sulfur-containing group and rigid fluorenyl group into the molecular structure was beneficial to improve its index of refraction.2.To prepare higher refractive index optical resins,the reaction of 4,4-dihydroxydiphenyl sulfide,4,4-dihydroxydiphenyl sulfone,and 9,9-bis[(4-hydroxy)phenyl]fluorene with epichlorohydrin under a base catalyst was used to synthesize 4,4-dihydroxydiphenyl sulfide diglycidyl ether(N-1),4,4-dihydroxydiphenyl sulfone diglycidyl ether(N-2),and 9,9-bis[(4-hy droxy)phenyl]fluorene diglycidyl ether(N-3),respectively.4,4-dihydroxydiphenyl sulfide dithioglycidyl ether(N-4),dihydroxydiphenyl sulfone dithioglycidyl ether(N-5),and 9,9-bis[(4-hydroxy)phenyl]fluorene dithioglycidyl ether(N-6)were prepared via a simple one-step reaction using the above-synthesized epoxy resin monomers.The epoxy and episulfide resin monomers were then subjected to ring-opening polymerization with an equimolar amount of 4,4-thiodibenzenethiol(TDBT)to obtain high refractive index epoxy and episulfide resin polymers(P-N-1-P-N-6).The Ts of P-N-1,P-N-2,and P-N-3 was higher than that of P-N-4,P-N-5,and P-N-6,indicating that the thermal stability of epoxy polymers was better than that of episulfide polymers.These epoxy and episulfide polymers except P-N-5 showed good optical transparency with the transmittance of>80%at the visible range.The refractive indices of P-N-1,P-N-2,and P-N-3 at a wavelength of 550 nm were 1.6847,1.6827,and 1.6932,respectively,indicating that the groups of the high content of sulfur and curing agent of TDBT enhanced the refractive indices of epoxy and episulfide polymers significantly.3.In order to study the nanoimprint performance of the high refractive index optical resin,the grating template with a line width of 480 nm and a period of 690 nm and 2D photonic crystal template with diameters of 50?400 nm were respectively nanoimprinted with M-1-M-6 including 0.1 wt%BPO and N-1/TDBT-N-6/TDBT for fabricating a series of grating structures and photonic crystals with a high refractive index.These optical resins except for N-2 exhibited excellent nanoimprint properties,and flexible groups such as ether,thioether,and methylene groups in the molecular structure contributed to their high fidelity and low defectivity,while strongly polar groups such as sulfone and thiadiazolyl groups showed precisely the opposite effect.4.To explore the application of the high refractive index optical resins in microlens,a series of microlenses PMM-1?PMM-6 and PMN-1?PMN-6 with diameters of 9.5 ?m,7.5?m and 5.5 ?m were successfully prepared base on their excellent nanoimprinting properties.These microlens structures except PMN-2 were consistent with the design one.The focal spot of most microlenses was bright,clear,high contrast with the surrounding environment,and light intensity distribution of the focal spot was axisymmetric and uniform,indicating contours of these microlenses were nanoimprinted well,which was consistent with the characterization of SEM.By analyzing the focal spot size(FWHM)of the microlens,it was known that all the microlenses exhibited different focusing powers due to the difference in refractive index,and the higher refractive index of a microlens the smaller its FWHM,then the better its property of focusing.The higher the index of refraction of a microlens,the smaller its FWHM,then the better its property of focusing.The FWHM of PMM-4 with a refractive index of 1.5793 and diameters of 9.5 ?m and 7.5 ?m was 1.4748 ?m and 1.1853?m,respectively.However,the FWHM of PMN-6 with a refractive index of as high as 1.7032 and diameters of 9.5?m and 7.5?m was 1.1084 ?m and 0.7052?m,respectively,which is much smaller than that of PMM-4,indicating that PMN-6 showed a better focusing property than PMM-4.