page_title: High-refractive-index polymer
section_title: Intrinsic HRIP
hierarchical_section_title: High-refractive-index polymer / Types / Intrinsic HRIP
caption_attribution_description: English: organometallic HRIP
context_page_description: A high-refractive-index polymer is a polymer that has a refractive index greater than 1.50.
  Such materials are required for anti-reflective coating and photonic devices such as light emitting diodes and image sensors. The refractive index of a polymer is based on several factors which include polarizability, chain flexibility, molecular geometry and the polymer backbone orientation.
  As of 2004, the highest refractive index for a polymer was 1.76. Substituents with high molar fractions or high-n nanoparticles in a polymer matrix have been introduced to increase the refractive index in polymers.
context_section_description: Sulfur-containing substituents including linear thioether and sulfone, cyclic thiophene, thiadiazole and thianthrene are the most commonly used groups for increasing refractive index of a polymer. Polymers with sulfur-rich thianthrene and tetrathiaanthracene moieties exhibit n values above 1.72, depending on the degree of molecular packing.
  Halogen elements, especially bromine and iodine, were the earliest components used for developing HRIPs. In 1992, Gaudiana et al. reported a series of polymethylacrylate compounds containing lateral brominated and iodinated carbazole rings. They had refractive indices of 1.67–1.77 depending on the components and numbers of the halogen substituents. However, recent applications of halogen elements in microelectronics have been severely limited by the WEEE directive and RoHS legislation adopted by the European Union to reduce potential pollution of the environment.
  Phosphorus-containing groups, such as phosphonates and phosphazenes, often exhibit high molar refractivity and optical transmittance in the visible light region. Polyphosphonates have high refractive indices due to the phosphorus moiety even if they have chemical structures analogous to polycarbonates. Shaver et al. reported a series of polyphosphonates with varying backbones, reaching the highest refractive index reported for polyphosphonates at 1.66. In addition, polyphosphonates exhibit good thermal stability and optical transparency; they are also suitable for casting into plastic lenses.
  Organometallic components result in HRIPs with good film forming ability and relatively low optical dispersion. Polyferrocenylsilanes and polyferrocenes containing phosphorus spacers and phenyl side chains show unusually high n values (n=1.74 and n=1.72). They might be good candidates for all-polymer photonic devices because of their intermediate optical dispersion between organic polymers and inorganic glasses.
caption: Organometallic HRIP
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