Isomer structure-optical property relationships for naphthalene-based poly(perfluorocyclobutyl ether)s

Abstract

Synthesis and characterization of new naphthalene-based PFCB aryl ether polymeric isomers with 1,5-, 1,6-, 2,6-, and 2,7-linkages were described. Monomers of perfluorocyclobutane (PFCB) poly(aryl ether)s, 1,5-, 1,6-, 2,6-, and 2,7-bis(trifluorovinyloxy)naphthalene, were synthesized from dihydroxynaphthalenes in two steps and polymerized by 2π + 2π step-growth cyclopolymerization. The naphthalene-based PFCB polymers (PFNs) had a relatively high Tg in the range 106−144 °C and excellent thermal stability at temperatures up to 400 °C. Among PFN polymeric isomers, Tg of the 1,5-linked PFCB polymer (1,5-PFN) was 30−40 °C higher than those of the other naphthalene isomers due to its high steric hindrance around the backbone. The refractive index and birefringence of the PFN polymers in the form of spin-coated films were determined. The PFN isomeric polymers showed tunability in refractive index and the birefringence of the order of 1,5 < 1,6 < 2,6 < 2,7-PFN and 1,5 < 1,6 < 2,7 < 2,6-PFN, respectively. PFN isomers had low birefringences below 0.002 except 2,6-PFN. The lowest value in birefringence was 0.0008 of 1,5-PFN due to its highly kinked structure. Plastic optical fibers of homopolymers, 1,5- and 2,7-PFN, and copolymers, 2,7-co-1,5-PFN and 2,7-PFN-co-6F−PF, were prepared, and optical losses and windows of them were observed. The attenuation loss of PFN polymers was about 0.17−0.27 dB/cm at the wavelength of near-IR optical sources. 1,5-PFN had a lower optical loss than 2,7-PFN. The optical loss of the 2,7-co-1,5-PFN copolymer was effectively reduced compared with that of 2,7-PFN. The lowest optical loss polymer for PFCB POF was 2,7-PFN-co-6F-PF of 0.07 dB/cm at the wavelength of the optical loss window and 0.17 dB/cm at 1300 nm.