Study On Epoxidation Of Low Molecule Weight Polyisobutene

Currently, the encapsulating materials used for LED packaging are mainly based onepoxy and silicone. But both epoxy and silicone encapsulantshave drawbacks. Siliconeencapsulants have low mechanical strength, high moisture permeability, poor interfacebonding and sealing as well as high purifying cost. Diglycidyl ether of bisphenol A (DGEBA)contains benzene rings and hydroxyl groups that will cause fast UV-yellowing and highmoisture absorption. Cycloaliphatic epoxy resinsare comprised of saturated molecules andexhibit excellent UV resistance.But the cross-linking density is high in the cured materials. Itbrings about high modulus, brittlenessand thermal stress.Also, the moisture absorption ofcycloaliophatic epoxy is high.Low molecule weight polyisobutene (LMPIB) possessesultrahigh purity, excellent transparency, outstanding UV resistance and low moisturepermeability. These features of LMPIB may make up the drawbacks of cycloaliophatic epoxyresins as LED encapsulants.In this thesis, LMPIBs with different molecular weight were epoxidized with peraceticacid generated in situ under the catalysis of acidic ionic exchange resin (IER). The obtainedproduct was identified with FT-IR and the effect of reaction conditions on the epoxidationof LMPIBs were investigated systematically. Meanwhile, pyrolysis was applied to LMPIB toincrease the double bonds in PIB molecules and prepare telechelic PIB. The structure of thepyrolytic product was analyzed with FT-IR and13C-NMR spectroscopes and the epoxidationof the pyrolytic PIB was investigated. The epoxidized LMPIBs (E-PIBs) were blended withhydrogenated DGEBA. The effect of the added EPIBs on the curing of hydrogenated DGEBAand dynamic properties of cured hydrogenated DGEBA were analyzed with DSC and DMA,respectively. The effect of EPIBs on the tensile property, impact resistance, transparency, UVresistance and water adsorption of cured hydrogenated DGEBA was investigated.Peracetic acid generated in situ could turn the end double bonds of LMPIBs into epoxygroups and produced a transparent liquid E-PIB. Esterification and hydroxylation mightaccompany the epoxidation reaction and reduce the yield. The IER could maintain itsefficiency after recycled4times. For LMPIBs with molecular weight from300to1000g/mol, the conversion of double bond could be86%and the yield of epoxy could be83%. Theepoxy groups in the produced E-PIB could be as high as0.130mol/100g.Pyrolysis would introduce β-type double bond to LMPIB. After pyrolysis at315℃for1.5h, the degree of unsaturation in PIB molecules could increased to1.54. The ratio of-double bond to β-double bond became1:3. The increase in unsaturation degree benefitedthe epoxidation of LMPIB and high epoxy value. DSC analysis indicated that the addedE-PIBs increased the incipient exothermic temperature of DGEBA and reduced the reactionheat during curing. DMA analysis demonstrated that phase separation occurred inDGEBA/E-PIB blends after curing. The compatibility of DGEBA with E-PIBs increasedwithincreasing the epoxy value of E-PIBs and decreasing the molecular weight of E-PIBs.After blended with E-PIBs, the properties of cured DGEBA as LED encapsulant wereimproved. The impact strength and elongation at break increased45%and60%at5phrE-PIB, respectively; while the tensile strength decreased8.7%. The UV resistance wasenhanced and the yellowing factor reduced50%at8phr E-PIB. The water adsorptionreduced20%at10phr E-PIB.