The Reasearches And Synthesis Of Polysiloxane Uesd To Power LED Encapsulation

After incandescent, fluorescent and HID (high-intensity dischargelamp), as the fourth lighting, LED (Light-Emitting Diode) has become oneof the fastest developing industries in the field of new energy. LEDencapsulating materials, as the most closely link contacted with market, havealways been research focus of new materials industry. With the developmentof powered LED devices, increasingly demanding on the optical properties(refractive index and light transmittance) of LED encapsulating materials isneeded. Higher hardness, better temperature resistance and bondingproperties are demanded simultaneously. So the original epoxy resin andmodified epoxy resin cannot meet the power LED packaging requirements.Currently, LED encapsulating materials of China accounting for65%of theworld, while encapsulating materials for high-power LED packaging canonly depend on expensive imports, which limits the development of ourcountry’s related industries seriously. Particularly since the financialcrisis in2008, development and application of high-power LED packaging rubberhas become the bottleneck of high-power LED packaging development. Therefore, important practical significance was showed in design andsynthesis of novel LED packaging materials.Polysiloxane was used as the base polymer of RTV silicone rubber. Themolecular structure of polysiloxane is the key factor of effecting theperformances of LED packaging glue as the first choice of novel LEDpackaging materials. Vinyl, epoxy and hydroxyl are usually terminated onthe polysiloxane. Different properties was showed by different functionalgroups. Therefore, design and synthesis of polysiloxane that meeting thepower LED packaging requirements can lay foundation for researching thehigh-power LED packaging rubber.In this paper, under the catalysis of tetramethylammonium hydroxide(Me4NOH）, different series of polysiloxane were synthesized by anionicring-opening polymerization. Analyzing their performances, influences ofvarious factors on RTV silicone rubber were investigated deeply, whichprovided some technical support for preparing RTV silicone rubber to meetthe requirements of powered LED packaging.Main contents are as follows:(1) The connection of polysiloxane’s molecular structure with refractiveindex was summarized through calculating the influences of differentfunctional groups on polysiloxane’s molar refraction by modifiedatomic contribution method. On this basis, RTV silicone with highphenyl was designed and synthesized. Comparing the index of refractive measured and the molar refraction calculated, the resultshows that the molar refraction calculated by modified atomcontribution method is in highly keeping with the real refractiveindex of the synthetic silicone rubber. For the molecular structure,the lager the volume group is, the more contribution of its contentmakes to the molecular refractive index.(2) Under the catalysis of tetramethylammonium hydroxide (Me4NOH),octamethyl siloxane (D4), tetramethyl tetraphenyl cyclotetrasiloxane（DPh4）and tetramethyl tetravinyl cyclotetrasiloxane（DVi4）wereterminated with different blocking agents (1,3-Bis(3-glycidoxypropyl)-1,1,3,3-tetramethyldisiloxane, divinyl tetramethyl disiloxaneand1,3-Bis(hydroxypropyl)tetramethyldisiloxane) by anionic ring-opening polymerization. The structure and performances of thesethree series of polysiloxane were researched. Viscosity and molecularweight of products were controlled by synthesis conditions andamount of raw materials. Influences of molecular structure on therefractive index, transmittance, heat resistance and adhesionproperties were summarized. The results show that a little epoxygroup brought into vinyl-terminated polysiloxane with methyl, vinyland phenyl can make the adhesion properties and mechanicalproperties better. Higher performance silicone was chosen for nextvulcanization reaction. (3) As the basic complexes, homemade polysiloxane were vulcanizatedwith different crosslinkers by certain ratio of Si-H：Si-CH=CH2. RTVsilicone rubbers with good optical performance (refractive indexabove1.52and transmittance above95%) were synthesized. Andinfluences of polysiloxane’s structure, crosslinker’s species andcrosslinker’s agent on the hardness of RTV silicone rubber weresummarized systematically, which providing efficacious theory basesfor researching RTV silicone rubber with high performances.