Polycaproamide Modified by Single-Walled Carbon Nanotubes as Protective Coating for Optical Fiber Olesya N. Zabegaeva,* Dmitry A. Sapozhnikov, Bato A. Baiminov, Anatoly V. Krestinin, Sergey L. Semjonov, Alexey F. Kosolapov, Evgeniy A. Plastinin, and Yakov S. Vygodskii New optical fiber coatings based on polycaproamide modified by carbon nanotubes have been tested. Nanocomposites were fabricated by in situ anionic polymerization of e-caprolactam in the presence of 0.005–0.01 wt.% single-walled carbon nanotubes functionalized with polyimide. It was found that obtained nanocomposites are able to form high-grade, heat and water resistant optical fiber coatings with improved mechanical strength. These as prepared fiber coatings are differed in high bending strength (6 GPa). Annealing for 3 and 72 h at temperatures high as 250 and 200  C respectively reduces the bending strength of such coated optical fiber by no more than 5%. 1. Introduction The primary factor restricting the application of optical fibers is their vulnerability to damages upon exploitation at high temperatures and aggressive ambient medium, which is primarily determined by protective coating properties. The main requirements to the protective polymer shell are its adhesion to optical fiber, elasticity, thermal and mechanical resistance. Widely used polyacrylate based protective polymer coatings allow optical fibers to be employed at temperatures no higher than 85  C and their modified analogues until 150  C. [1] Moreover, they are quite sensitive to the many chemicals in the ambient medium. Currently protective coatings based on polyimides are the most progressive. Polyimides provide improved thermal stability, oil, acid resistance and etc. [2,3] Meanwhile the main drawbacks of polyimides are the multistep coating method due to utilization of poly(amic acid) precursor which poses a problem of incomplete imidization [4] and subsequent stability of the final coating, insufficient adhesion to the fiber and significant variation in mechanical strength. Polyamides (PA) are one of the most available polymers with good adhesive properties, mechanical, and chemical sta- bilities. (Co)polymers and composites based on PA are used in different modern technologies in particular they widely used as coatings. [5,6] Due to low friction coeffi- cient and high wear resistance PA are primarily utilized for the manufacture of secondary or external protective shell. [7–10] The introduction of modifying additives in PA allows change almost all their exploitation characteristics and obtain the products with tuned properties. The formulation PA blends with polyolefines, melamine cyanurates, different types of elastomers, polyacrylates, epoxide resins and ets., promotes a smooth uniform coating formation with improved mechanical strength and increased water and/or fire-resistance. [11–13] The main disadvantage of such coatings is their low bending strength at high temperatures. Previously [14] we have reported about significant improve- ment of polycaproamide (PCA), commonly known as nylon-6, performance properties by in situ anionic polymerization of e-caprolactam in the presence of single-walled carbon nanotubes (SWCNTs) functionalized with polyimides (PI). PI macro- molecules incorporated on SWCNTs surface are active in the polymerization process and contribute to the formation of covalent bonding between the individual nanotube and PCA matrix, thus providing their homogeneous distribution within the polymer as well as outstanding reinforcing effect. Thus, the thermal stability, Izod impact strength of polymer blocks as well as tensile strength and elongation of polymer films have been significantly improved. [14] The goal of this study is to state the possibility of PCA/ SWCNT composites application for optical fiber coatings. PCA composites were obtained by anionic in situ polymerization of e-caprolactam in the presence of 0.005–0.01 wt.% of function- alized SWCNTs. Afterwards the stable, uniform solutions of composites in formic acid were prepared and further utilized for optical fiber coatings formulation. For comparison among the tested PCA nanocomposites there were neat PCA and copolymer based on PCA with PI. The influence of polymer solution O. N. Zabegaeva, D. A. Sapozhnikov, B. A. Baiminov, Y. S. Vygodskii A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 28 ul. Vavilova, 119991 Moscow, Russia E-mail: pashkova81@list.ru A. V. Krestinin Institute of Problems of Chemical Physics, Russian Academy of Sciences, 1 prosp. Akad. Semenova, 142432 Chernogolovka, Moscow Region, Russia S. L. Semjonov, A. F. Kosolapov, E. A. Plastinin Fiber Optics Research Center, Russian Academy of Sciences, ul. Vavilova 38, 119333 Moscow, Russia DOI: 10.1002/masy.201700027 Macromolecular Symposia Anionic ring-opening polymerization www.ms-journal.de ARTICLE Macromol. Symp. 2017, 375, 1700027 © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1700027 (1 of 7)