| As a new type of solid light source, Light emitting diodes (LEDs) have lots ofadvantages compared with the traditional lighting equipments, such as energy conservation,environmentally friendly, fast response and long-life. LEDs have been used widely in backlights of displays, traffic lights, car lights, general lighting, and many other fields.Conventional LEDs are encapsulated in epoxy resins and, when is used, tend to yellow inhigh temperature and easy to crack because of strong internal stress, which can hardly meetthe requirements of power type LED encapsulation. Organic silicon materials have lots ofexcellent properties, such as good mechanical properties, adhesive performance, heatresistance, high optical transmittance, etc., which naturally become the best choice for LEDpackaging. So the preparation of organic silicon encapsulating materials with highperformance becomes a research hotspot in this field.In this paper, the research, on the whole, consists of two parts: preparation and propertiesresearch of organic silicon encapsulating materials with low refractive index (RI), another onewith high RI.For the first part, Vinyl-terminated polydimethylsiloxanes (Vi-PViMS) andVinyl-terminated polydimethylvinylsiloxanes (Vi-PViMS) with low RI were firstly preparedby anionic ring-opening polymerization of octamethylcyclotetrasiloxane (D4), tetravinyltetramethylcyelo tetrasiloxane(D4Vi) and diethenyl-1,1,3,3-tetramethyldisiloxane(MMVi).The research results showed that the optimum technological conditions are as follows: thepolymerization temperature110℃, polymerization time4h, catalyst dosage0.08%.Then, polymethylhydrosiloxanes (H-PMHS) with were synthesized by ring-openingpolymerization of the mixture of D4, methylhydrogencyclosiloxane(D4H) andtetramethyldisiloxane(MMH). The research results showed that the optimum technologicalconditions are as follows: the polymerization temperature65℃, polymerization time4h,catalyst dosage2%.For the second part, methylphenylcyclosiloxanes (DnMe,Ph) was prepared through the hydrolysis-polycondensation-catalytic cracking process based on methylphenyldichloros.Vinyl-terminated polymethylphenylsiloxanes (Vi-PDMS-PMPS) and Vinyl-terminatedpolymethylvinylphenylsiloxanes (Vi-PDMS-PViMS-PMPS) with were prepared using D4,D4Vi, DnMe,Phand MMVias raw materials, which had the RI of1.52~1.53. The experimentalresults showed that the best dosage of D4in the formula was9%~15%.Then, polymethylphenylhydrosiloxanes (H-PMHS-PMPS) with were synthesized bycation ring-opening polymerization of the mixture of DnMe,Ph, D4Hand MMH. Theexperimental results indicated that optimum dosage of D4Hshould be less than35%, whichcan avoid compatibility problems.The structure of the products was characterized by means of Fourier infraredspectrometer (FT-IR) and nuclear magnetic resonance instrument (1H-NMR). And thethermogravimetric analysis (TG) results showed that each product had good thermal stability.Finally, different vinyl silicone oil and hydrogen silicone oil were cured. Then, two typesof encapsulation formulas for LEDs were obtained by investigating the properties of the curedmaterials, such as hardness, tensile strength. The encapsulation formulas were as follows:(1) Low RI system: The main polymers consisted of V1and MQ resin, and thehydrogen silicone oil was selected of which the hydrogen content was0.75%, the viscositywas118~224mPa·s and the molar ratio was nSi-H/nSi-Vi=1.3~1.5. A transparent andthermostable packaging material with Shore A hardness of62~66degree, tensile strength of4.94~5.45MPa, breaking elongation rate of231%was obtained by using the conditionsabove.(2) High RI system: The main polymer should be V9, and H9was selected as crosslinkingagent, of which the hydrogen content is0.3%, the viscosity is105mPa·s, and the molar ratiowas nSi-H/nSi-Vi=1.3~1.5. The cured materials were high transparent gel, which werethermostable and had a light transmittance above95%, and can be used as LED fillermaterials. |
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