Platinum free thermally curable siloxanes for optoelectronic application – synthesis and properties

Abstract

Polysiloxanes for applications in the area of optical devices are usually based on two-component platinum catalysed cross-linked materials. Here we report the synthesis and properties of a novel one-component siloxane that can be thermally cured showing similar tailorable properties like commercially available encapsulation systems without using a noble metal catalyst. The pre-curing material is formed by an acid catalysed condensation reaction of trialkoxysilanes (TAS), dialkoxysilanes (DAS) and alkoxy-terminated polysiloxanes. NMR analysis of the formed polymeric compounds reveal that the materials are partially cross-linked gels. The obtained compounds can be thermally cured and consolidated at temperatures between 160 and 200 C. Depending on the composition a tuneable hardness in between 50-90 Shore A, refractive indices of 1.494-1.505, as well as high temperature stabilities up to 443 C were obtained.The high thermal-and photostability, the high transparency, as well as the tailorable refractive index makes these materials to ideal systems for optoelectronic applications. Investigations under increased temperatures and high-density illumination reveal that the material can withstand conditions, which are typical for high-performance light emitting diodes (LED).

Thermoplastic Silsesquioxane Hybrid Polymers with a Local Ladder-Type Structure

“…However, the comparison of the area of the visible peaks in the 13 C CP-MAS NMR indicates that the number of −OMe groups is lower after consolidation (Figure c) Figure a,b) of the polymers show two peaks in the range of −74 to −66 and −80 to −77 ppm that can be assigned to T 2 and T 3 species . The lack of T 0 signals shows a complete integration of the precursor trialkoxysilane in condensed species.…”

“…Using the so-called “gel-melting method”, the researchers obtained organically modified siloxanes with low softening points . Klein et al also developed various one-, two-, and three-component melting gels containing phenyl and methyl substituents as organic groups. ,, Their focus was mainly on the investigation of thermal stability, the relationship between structure, glass transition temperature ( T g ), and consolidation temperature ( T con ), and the development of possible applications. , Previously, we showed that the concept can be applied for optoelectronic materials and can be expanded to an elastomer-like behavior . However, none of these previous studies has investigated in detail the mechanism of the unusual behavior of these materials.…”

“…Silsesquioxanes are known for decades; especially, cage compounds have attracted a lot of attention in the 20th century. , Derivatives of these compounds are partially condensed cages and ladderlike silsesquioxanes . Since the first structural characterizations, the field of silsesquioxanes has greatly expanded and the molecules are used as building blocks for inorganic–organic hybrid materials in a wide range of areas, such as pharmacy or aerospace. − Their outstanding optical properties make them ideal materials for optoelectronic applications, such as LED encapsulants . Structures of silsesquioxanes can vary from open or closed cagelike oligosilsesquioxanes consisting of discrete structures formed from a limited number of tetrahedral units to polymeric species with a defined ladder structure or random networks (Figure ).…”

“…5−8 Their outstanding optical properties make them ideal materials for optoelectronic applications, such as LED encapsulants. 9 Structures of silsesquioxanes can vary from open or closed cagelike oligosilsesquioxanes consisting of discrete structures formed from a limited number of tetrahedral units to polymeric species with a defined ladder structure or random networks (Figure 1). 10 Oligo-or polysilsesquioxanes are commonly synthesized by polycondensation reactions based on the sol−gel process.…”

“…26,27 Previously, we showed that the concept can be applied for optoelectronic materials and can be expanded to an elastomer-like behavior. 9 However, none of these previous studies has investigated in detail the mechanism of the unusual behavior of these materials.…”