High Refractive Index Polymers (n > 1.7), Based on Thiol–Ene Cross-Linking of Polarizable P═S and P═Se Organic/Inorganic Monomers

Abstract

A new class of high refractive index polymers was developed through the thiol−ene coupling reaction of trivinylphosphine chalcogenides, [(CH 2 CH−)3PX (X = S, Se)], with 1,2-ethane dithiol and 1,3-benzene dithiol. The polymers were obtained through a thermal initiation and polymerization process which yielded robust monolithic materials. The polymers have good transmission properties in the visible region of the spectrum with very high refractive indices ranging from 1.66 to 1.75, placing them in the top echelon of high refractive index polymers, with Abbe numbers between 22 and 31. The high refractive index is due, in large part, to the presence of the highly polarizable PS and PSe groups, which have molar refractivities of 13.84 and 17.33 mol/cm 3 , respectively. The polymers tend to have a high cross-link density that varies with the composition but results in rigid materials for most compositions. The glass-transition temperatures (T g ) for all but one composition were above 70 °C, and the storage moduli ranged from 1.5 to 3.8 GPa. The 1,2-ethane dithiol compositions had lower values of T g than the 1,3-benzene dithiol materials. This was attributed to a lower cross-link density in the 1,2-ethane dithiol polymers, as determined from the residual unreacted vinyl groups measured by Raman spectroscopy and 31 P solid-state nuclear magnetic resonance spectroscopy. The PSe polymers were slower to react and required higher temperatures; they also produced the hardest materials with the highest refractive indices.

Photoclick Chemistry: A Bright Idea

“…Furthermore, the step-growth mechanism of thiol-X photopolymerization results in polymer network with low intrinsic shrinkage stress with minimum leachable monomers and exceptional resistance to oxygen inhibition. While there exist several recent reports on high refractive index polymers based on radical thiol–ene reactions, a majority of these strategies rely on thermal or self-initiated polymerizations. − Incorporation of more polarizable groups such as P = S and P = Se and highly polarizable main group elements such as Si, Ge, Sn, etc., enabled these polymers to achieve a refractive index as high as 1.75 with excellent optical transparency.…”

Synthesis and Properties of High‐Refractive‐Index Iodine‐Containing Polyacrylates

“…Thus, various attempts have been made to increase the n D of polyacrylates. For example, sulfur- [41][42][43] and seleniumcontaining [44][45][46] polyacrylates with n D values of 1.60 and 1.70 have been reported. Furthermore, an iodine-containing polyacrylate showed an n D of 1.77.…”

High Refractive Index Photopolymers by Thiol–Yne “Click” Polymerization

“…Thus, efforts to improve the refractive indices of these materials mainly focused on introducing groups or atoms with high molar refraction . While significant progress has been made in the development of intrinsic HRIPs, the majority of these strategies rely on thermally driven polymerization techniques that suffer from a lack of optical transparency and spatial and temporal control. − However, to achieve high performance in various applications including additive manufacturing, , GRIN optics, and HOEs, , polymers with refractive indices ranging from 1.3 to >1.6 are highly desirable. The design and synthesis of such high-performance HRIP materials require the use of the best available organic and polymer synthetic strategies such as thiol-X “click” chemistry.…”