Highly refractive, transparent, and solution processable polyamides based on a noncoplanar ortho-substituted sulfonyl-bridged diacid monomer containing chlorine side groups

Abstract

A novel ortho-substituted sulfonyl-bridged diacid monomer (DA-SO2) containing flexible methylene and ether linkages and chlorine side groups was synthesized. A series of new organic-soluble polyamides (PAs) bearing flexible linkages and bulky sulfonyl moieties were synthesized from DA-SO2 and various commercially available aromatic diamines (1–5) via a direct polycondensation method with triphenyl phosphite and pyridine. The resulting polymers were obtained in high yields and possessed inherent viscosities in the range of 0.30–0.85 dL g−1. All of the polymers were amorphous in nature, exhibited excellent solubility and could be easily dissolved in amide-type polar aprotic solvents (e.g., N-methyl-2-pyrrolidone, dimethyl sulfoxide, N,N-dimethylacetamide, and dimethylformamide), and even dissolved in less polar solvents (e.g., tetrahydrofuran, pyridine, and acetone). They showed good thermal stability with glass transition temperatures between 172 and 235 °C and 10 % weight loss temperatures in excess of 401 °C in nitrogen and 380 °C in air atmosphere. The flexible structure endowed the PA films with good optical transparency. The optical transmittances of the PA films at 450 nm were higher than 90 % for the thickness of approximately 10 μm. The combination of the chlorine and sulfonyl groups as well as the flexible methylene and ether linkages provided PAs with high average refractive indices (nav) of 1.7069–1.7245 and low birefringences (Δn) of 0.0061–0.0073 at 632.8 nm.