Preparation of <scp>ultraviolet</scp>‐cured silicone elastomer reinforced by <scp>SH</scp>‐<scp>POSS</scp> crosslinker for <scp>light emitting diode</scp> encapsulant

Abstract Stable silicone encapsulants are essential for protecting high‐power light‐emitting diodes (LED) from dust and moisture and extending their service life. Herein, by incorporating thiol‐functionalized polyhedral oligomeric silsesquioxane (SH‐POSS) as a crosslinker into ultraviolet‐curable silicone elastomer (UVSE), a series of new UV‐cured silicone encapsulants (SH‐POSS/UVSE) have been developed through thiol‐ene click chemistry. It was found that SH‐POSS effectively enhanced the mechanical properties of SH‐POSS/UVSE. When 30 mol% SH‐POSS was added, the tensile strength and elongation at break reached 1.01 MPa and 422%, respectively, 2.1 and 1.6 times higher than pure UVSE. This could be ascribed to the more concentrated crosslinking network and the improved interfacial interactions between SH‐POSS and UVSE than physical blending. Moreover, the steric effect of branched and rigid SH‐POSS restricted the movement of UVSE molecular chains. Incorporating SH‐POSS also suppressed UVSE degradation and improved its thermal stability. Additionally, when the LED sample encapsulated by SH‐POSS/UVSE‐30 was immersed in boiling red ink for 2 h, no crack or stain was observed, indicating that SH‐POSS/UVSE‐30 possessed good adhesion to the LED lead frame. This work provides a new approach to fabricating high‐strength and stable silicone composites, which are promising candidates as LED encapsulants.