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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. [ABSTRACT FROM AUTHOR]

The focus of this review is the fundamentals of the transition metals catalyzed atom transfer radical polymerization. The mechanistic understanding of this process and its synthetic applications have been analyzed and discussed.

The kinetics underlying the homogeneous atom transfer radical polymerization (ATRP) of styrene were investigated via experiments using 4,4'-dialkyl substituted 2,2'-bipyridines as the solubilizing agent. The polymerizations, which demonstrated internal first-order kinetics with respect to the monomer, initiator and copper(I) halide concentration, showed an optimum ligand-to-copper(I) halide ratio of 2:1 and a direct relationship between molecular weight increase and the ratio of monomer consumed to the initial initiator concentration.

This paper reports the transition metal‐free C(sp3)−H sulfenylation of arylacetamides by using thiophenols as the sulfenyl reagents. The reactions take place in the presence of only K3PO4. Control experiments indicate that the reactions proceed via a featured sulfur‐centred free radical intermediate. In addition, the synthesis of 2‐thiomethyl benzoxazoles has been realized via the p‐toluenesulfonic acid (p‐TSA) promoted annulation of the sulfenylated products. [ABSTRACT FROM AUTHOR]

A radical polymerization process that yields well-defined polymers normally obtained only through anionic polymerizations is reported. Atom transfer radical polymerizations of styrene were conducted with several solubilizing ligands for the copper(l) halides: 4,4'-di-tert-butyl, 4,4'-di-n-heptyl, and 4,4'-di-(5-nonyl)-2,2'-dipyridyl. The resulting polymerizations have all of the characteristics of a living polymerization and displayed linear semilogarithmic kinetic plots, a linear correlation between the number-average molecular weight and the monomer conversion, and low polydispersities (ratio of the weight-average to number-average molecular weights of 1.04 to 1.05). Similar results were obtained for the polymerization of acrylates., Szwarc and Levy first reported on living anionic polymerizations in 1956 (1, 2), and this technique made it possible to prepare well-defined polymers. A living polymerization is a chain-growth polymerization [...]