High refractive index of transparent acrylate polymers functionalized with alkyl sulfur groups

Several sulfur-containing acrylate polymers were developed for a high refractive index with high transparency and good processing performance for thin films. A series of poly(methacrylate)s were synthesized by radical polymerization, in which thin films are coated on a quartz substrate for optical characterization. One, two and three sulfur atoms were bound into acrylate monomers and thermally copolymerized with methyl methacrylate. An alicyclic structure was used to achieve a dense molecular volume of the sulfur-containing monomer. Refractive index was measured under visible light. The index linearly increased with the sulfur-containing monomer content of the copolymer. Each homopolymer was predicted by an extrapolation method, resulting in a high refractive index of 1.624–1.725 at 589 nm. An Abbe's number of ∼30 was recorded for most sulfur polymers, indicating low wavelength dispersion of the index. A polymer with dipolar functionality displayed an Abbe's number of 40.9. High optical transparency of films was observed at the wavelengths of the index measurement. All polymers were thermally stable up to ∼250 °C and exhibited glass transition around 100 °C. Sulfur-containing acrylic monomers were developed for high refractive index. The index of polymer films increased with the number of sulfur atoms in the monomer structure. Trisulfur-acrylic polymer provided refractive indices of more than 1.72 at visible light. Dipolar phenyl structure significantly increased the refractive index of acrylic polymers. Wavelength dispersion of the refractive index was investigated with Abbe's number of ca. 30 for all polymer films, except for the dipolar polymer viewing Abbe's number of ∼41.