High-Refractive-Index Polysiloxanes Containing Naphthyl and Phenanthrenyl Groups and Their Thermally Cross-Linked Resins

Abstract

High-refractive-index polysiloxanes containing naphthyl, phenanthrenyl, phenyl, and methyl groups have been synthesized using a polycondensation reaction starting from substituted di- and trialkoxysilanes. The obtained polymers comprised linear siloxane and partially cross-linked silsesquioxane units and showed optical transparencies of up to 99% at a thickness around 120 μm and high refractive indices of up to 1.622. The polymeric structures contained stabilized silanol groups that were further cross-linked at increased temperatures of 200 °C resulting in the formation of hybrid inorganic–organic resins. These typical thermal treatments at 200 °C for 72 h kept the transparencies as high as 98% and slightly lowered the RIs to values up to 1.610. A detailed structure evaluation of the resulting systems showed, depending on the size of the polycyclic aromatic substituent, excimer formation, which is based on weak interactions of the aromatic groups in the polymeric material. After thermal consolidation, glass-transition temperatures of the cross-linked systems were in the range of 18–74 °C depending on the composition. Thermal stabilities of the final resins reached higher values than commonly used siloxane resins up to 470 °C. The final materials are potential resins for high-temperature optical applications.

Oligo‐Condensation Reactions of Silanediols with Conservation of Solid‐State‐Structural Features.

“…[13] The reaction environment and the substitution pattern at the silicon atoms also influences the properties of the resulting oligo-and polysiloxanes, such as the glass transition temperature (T g ) [14][15][16][17][18] or the RI. [19][20] Different stable monosilanols, silanediols and -triols are already described in literature, such as Ph 3 SiOH, [21] Et 3 SiOH, [21] (n-Bu) 3 SiOH, [21] (tert-BuO) 3 SiOH, [22] Me 2 Si(OH) 2 , [23] Ph 2 Si(OH) 2 , [24] (cis-C 6 H 11 ) 2 Si(OH) 2 , [25] (tert-Bu) 2 Si(OH) 2 , [10] (ortho-tolyl) 2 Si(OH) 2 , [26] (iso-propyl) 2 Si(OH) 2 [27] PhSi(OH) 3 , [28] c-C 6 H 11 Si(OH) 3 [29][30] and tert-BuSi(OH) 3 . [31] Silanediols have been already used, for example, in the synthesis of LED encapsulation resins and in pharmaceutical applications, [24,[32][33] monosilanols were applied as catalysts for various organic syntheses, such as cross coupling reactions [34][35][36] or direct amidation of carboxylic acid [37] and silanetriols have already been used for the synthesis of various metallasiloxanes [38][39] and POSS cages.…”

“…As in other substitution reactions, the sterical environment at the silicon center to be attacked also plays a major role in the reactivity [13] . The reaction environment and the substitution pattern at the silicon atoms also influences the properties of the resulting oligo‐ and polysiloxanes, such as the glass transition temperature (T g ) [14–18] or the RI [19–20] …”

Low birefringence and low dispersion aliphatic thermosets with a high and tunable refractive index

“…1,2 Over the past few decades, a wide variety of HRIPs, both thermoplastics and thermosets, have been developed from the design principles based on the Lorentz-Lorenz equation. Notable HRIPs include acrylates, 5-7 polysiloxanes, 8,9 poly(arylene ether)s and poly(arylene thioethers), 10 polyphosphazenes, and thermosets from thiolene crosslinking reactions. [11][12][13][14][15] While the refractive index (n) of an HRIP is its defining feature, there are other parameters crucial for its wide applicability.…”

Photo‐Crosslinkable Inorganic/Organic Sulfur Polymers

“…Fabrication of these polymer systems heavily rely on thermal-initiated cross-linking methods and processes. [19][20][21][22] Within inverse vulcanization, these thermal curing times range from 1 to 96 h depending on the curing temperature. This limitation of current thermal processing procedures hinders design freedom and inhibits potential capabilities.…”