ORIGINAL PAPER Highly refractive, transparent, and solution processable polyamides based on a noncoplanar ortho -substituted sulfonyl-bridged diacid monomer containing chlorine side groups Hossein Kiani & Mohamed Mahmoud Nasef & Ali Javadi & Ebrahim Abouzari-Lotf & Firouzeh Nemati Received: 9 May 2013 /Accepted: 19 August 2013 /Published online: 29 August 2013 # Springer Science+Business Media Dordrecht 2013 Abstract A novel ortho -substituted sulfonyl-bridged diacid monomer (DA-SO 2 ) containing flexible methylene and ether linkages and chlorine side groups was synthesized. A series of new organic-soluble polyamides (PAs) bearing flexible link- ages and bulky sulfonyl moieties were synthesized from DA- SO 2 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 -meth- yl-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 tempera- tures 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 μ m. The combination of the chlorine and sulfonyl groups as well as the flexible methylene and ether linkages provided PAs with high average refractive indices (n av ) of 1.7069–1.7245 and low birefringences (Δn ) of 0.0061–0.0073 at 632.8 nm. Keywords Polyamide . Soluble . Refractive index . Transparency . Birefringence Introduction Demand for high refractive index (high-n ) polymers with low birefringence and high optical transparency has recently in- creased for advanced optical applications such as optical ad- hesives or encapsulants for organic light-emitting diode de- vices (OLED), microlenses for charge-coupled devices (CCD), antireflective (AR) coatings, and complementary metal oxide semiconductor (CMOS) image sensors [1–4]. The high-n , combined with high optical transparency, low birefringence (Δn ), and thermal stability are the main important factors for these applications. Recent progress in optical high-n polymers, applications in typical high-tech fields, and important method- ologies for increasing the refractive index values of polymers was reviewed in the feature article of Liu and Ueda [5]. Based on the Lorentz-Lorenz equation, the introduction of substituents with high molar refractions (R M ), low molar vol- umes (V M ), or high density can increase the refractive indices of conventional polymers. Therefore, metallic elements, aro- matic rings, sulfur, and halogens except fluorine have been H. Kiani : F. Nemati (*) Department of Chemistry, Faculty of Science, Semnan University, Semnan, Iran e-mail: fnemati@semnan.ac.ir F. Nemati e-mail: fnemati_1350@yahoo.com M. M. Nasef : E. Abouzari-Lotf (*) Institute of Hydrogen Economy, Universiti Teknologi Malaysia, Jalan Semarak, 54100 Kuala Lumpur, Malaysia e-mail: ebrahim@ic.utm.my E. Abouzari-Lotf e-mail: e.abouzari@gmail.com A. Javadi Faculty of Chemistry, Kharazmi University (former Tarbiat Moallem University), 15719-14911 Tehran, Iran J Polym Res (2013) 20:247 DOI 10.1007/s10965-013-0247-9