Synthesis of Aromatic Conjugated Main Chain Azobenzene Polymers and Their Properties

Abstract

Azobenzene polymers have great potential and impact on fundamental and applied research. However little is known about their thermal stability and degradation behaviours. Herein, nine conjugated main chain azobenzene polymers were synthesized using the nitroamine derivatives of some diphenylene compounds such as 4-amino-4′-nitrobiphenyl 1, 4-amino-4′-nitrobiphenyl ether 2 and 4-amino-4′-nitrobiphenyl sulfide 3, and comonomers triphenylamine A, N-methyldiphenyl amine B and triphenylphosphine C via diazo coupling reaction. These heteroatom containing polymers were characterized by 1H- and 31P-NMR, FTIR, UV–Vis and Raman spectroscopy. The thermal stability and degradation behaviour of these polymers were studied by means of TGA technique. Electronic spectra of the polymers recorded in DMF showed two strong maxima at ca. 280 and 380 nm. They were resistant to heat up to 270 °C and, produced 41-61% char under a nitrogen atmosphere at 800 °C. UL 94 burning tests performed for TPU Ravathane® (TPE-U) with added azobenzene polymer revealed that these polymers could be used as an intumescent reactive flame retardant additive, particularly for polyurethanes and elastomers, due to their high char yield at relatively high temperatures (e.g 800 °C). The carbonized materials were further characterized by XRD and SEM/EDX. 

Keywords

• Main chain azobenzene polymers; intumescent flame retardant additive; thermal stability; thermal degradation and carbonization

References

1. [1] Izumi A, Nomura R, Masuda T. Design and synthesis of stimuli-responsive conjugated polymers having azobenzene units in the main chain. Macromolecules 2001;34:4342-7.
2. [2] Yager KG, Barrett CJ. Azobenzene Polymers for Photonic Applications. Smart Light-Responsive Materials: John Wiley & Sons, Inc.; 2008. p. 1-46.
3. [3] Yager KG, Barrett CJ. Amorphous Azobenzene Polymers for Light-Induced Surface Patterning. Smart Light-Responsive Materials: John Wiley & Sons, Inc.; 2008. p. 145-75.
4. [4] Zollinger H. Front Matter. Diazo Chemistry I: Wiley-VCH Verlag GmbH & Co. KGaA; 2004. p. i-xiii.
5. [5] Nuyken O, Scherer C, Baindl A, Brenner AR, Dahn U, Gartner R, et al. Azo-group-containing polymers for use in communications technologies. Progress in Polymer Science 1997;22:93-183.
6. [6] Xie S, Natansohn A, Rochon P. Recent Developments in Aromatic Azo Polymers Research. Chemistry of Materials 1993;5:403-11.
7. [7] Viswanathan NK, Kim DY, Bian SP, Williams J, Liu W, Li L, et al. Surface relief structures on azo polymer films. Journal of Materials Chemistry 1999;9:1941-55.
8. [8] Cojocariu C, Rochon P. Light-induced motions in azobenzene-containing polymers. Pure and Applied Chemistry 2004;76:1479-97.

9. [9] Jiang XY, Chen XB, Yue XG, Zhang JJ, Guan SW, Zhang HB, et al. Synthesis and characterization of photoactive poly(arylene ether sulfone)s containing azobenzene moieties in their main chains. Reactive & Functional Polymers 2010;70:616-21.
10. [10] Jung WH, Ha EJ, Chung ID, Lee JO. Synthesis of aniline-based azopolymers for surface relief grating. Macromolecular Research 2008;16:532-8.
11. [11] Apaydin DH, Akpinar H, Sendur M, Toppare L. Electrochromism in multichromic conjugated polymers: Thiophene and azobenzene derivatives on the main chain. Journal of Electroanalytical Chemistry 2012;665:52-7.
12. [12] Acierno D, Amendola E, Bugatti V, Concilio S, Giorgini L, Iannelli P, et al. Synthesis and characterization of segmented liquid crystalline polymers with the azo group in the main chain. Macromolecules 2004;37:6418-23.
13. [13] Faghihi K, Hagibeygi M. New aromatic polyamide with Azo and phosphine oxide groups in the main chain. Turkish Journal of Chemistry 2007;31:65-73.
14. [14] Balasubramanian S, Kim J, Kim DY, Kumar J, Tripathy SK. Water soluble, conjugated main chain azo polymer: Synthesis and characterization. Macromolecular Rapid Communications 1996;17:853-7.
15. [15] Wu YL, Natansohn A, Rochon P. Photoinduced birefringence and surface relief gratings in novel polyurethanes with azobenzene groups in the main chain. Macromolecules 2001;34:7822-8.
16. [16] Papagiannouli I, Iliopoulos K, Gindre D, Sahraoui B, Krupka O, Smokal V, et al. Third-order nonlinear optical response of push-pull azobenzene polymers. Chemical Physics Letters 2012;554:107-12.
17. [17] Li ZA, Zeng Q, Yu G, Li Z, Ye C, Liu YQ, et al. New azo chromophore-containing conjugated polymers: Facile synthesis by using "Click" chemistry and enhanced nonlinear, optical properties through the introduction of suitable isolation groups. Macromolecular Rapid Communications 2008;29:136-41.
18. [18] Timpu D, Barboiu V, Airinei A, Rusu E. Transparent layers of azo-conjugated polymers: Preparation and opto-electrical properties. Journal of Optoelectronics and Advanced Materials 2000;2:531-5.
19. [19] Fernandez B, Oyarzabal I, Seco JM, San Sebastian E, Fairen-Jimenez D, Gomez-Ruiz S, et al. Luminescence and Magnetic Properties of Two Three -Dimensional Terbium and Dysprosium MOFs Based on Azobenzene-4,4 '-Dicarboxylic Linker. Polymers 2016;8.
20. [20] Izumi A, Teraguchi M, Nomura R, Masuda T. Synthesis of poly(p-phenylene)-based photoresponsive conjugated polymers having azobenzene units in the main chain. Macromolecules 2000;33:5347-52.
21. [21] Izumi A, Teraguchi M, Nomura R, Masuda T. Synthesis of conjugated polymers with azobenzene moieties in the main chain. Journal of Polymer Science Part a-Polymer Chemistry 2000;38:1057-63.
22. [22] Yao JL, You YJ, Lei YA, Dong LJ, Xiong CX, Sun ZG. Main-chain azo polyaramides with high thermal stability and liquid crystal properties. Journal of Polymer Research 2009;16:455-60.
23. [23] Liu BW, Zhao HB, Tan Y, Chen L, Wang YZ. Novel crosslinkable epoxy resins containing phenylacetylene and azobenzene groups: From thermal crosslinking to flame retardance. Polymer Degradation and Stability 2015;122:66-76.
24. [24] Ozarslan O, Yilmaz T, Yildiz E, Fiedeldei U, Kuyulu A, Gungor A. The preparation of perfectly alternating poly(amide-imide)s via amide unit containing new diamine. Journal of Polymer Science Part a-Polymer Chemistry 1997;35:1149-55.
25. [25] Vogel AI, Furniss BS. Vogel's Textbook of Practical Organic Chemistry: Longman Scientific & Technical; 1989.
26. [26] Bigelow HE, Robinson DB. Azobenzene. Organic Syntheses 1942;22:28-9.
27. [27] Georgi U, Reichenbach P, Oertel U, Eng LM, Voit B. Synthesis of azobenzene-containing polymers and investigation of their substituent-dependent isomerisation behaviour. Reactive & Functional Polymers 2012;72:242-51.
28. [28] Kaczmarek H, Ziegler-Borowska M, Chylinska M, Kowalonek J, Wolnicka M. Effect of azobenzene derivatives on the photochemical stability of poly(methyl methacrylate) films. Polymer Degradation and Stability 2012;97:1305-13.
29. [29] Pawelec W, Aubert M, Pfaendner R, Hoppe H, Wilen CE. Triazene compounds as a novel and effective class of flame retardants for polypropylene. Polymer Degradation and Stability 2012;97:948-54.
30. [30] Georgakilas V, Perman JA, Tucek J, Zboril R. Broad Family of Carbon Nanoallotropes: Classification, Chemistry, and Applications of Fullerenes, Carbon Dots, Nanotubes, Graphene, Nanodiamonds, and Combined Superstructures. Chemical Reviews 2015;115:4744-822.
31. [31] Simpson CD, Brand JD, Berresheim AJ, Przybilla L, Rader HJ, Mullen K. Synthesis of a giant 222 carbon graphite sheet. Chemistry-a European Journal 2002;8:1424-9.
32. [32] Bayazit MK, Moniz SJA, Coleman KS. Gram-scale production of nitrogen doped graphene using a 1,3-dipolar organic precursor and its utilisation as a stable, metal free oxygen evolution reaction catalyst. Chemical Communications 2017;53:7748-51.
33. [33] Ozarslan O, Bayazit MK, Catiker E. Preparation and Properties of Flame Retardant Poly(urethane-imide)s Containing Phosphine Oxide Moiety. Journal of Applied Polymer Science 2009;114:1329-38.
34. [34] Jing XK, Wang XS, Guo DM, Zhang Y, Zhai FY, Wang XL, et al. The high-temperature self-crosslinking contribution of azobenzene groups to the flame retardance and anti-dripping of copolyesters. Journal of Materials Chemistry A 2013;1:9264-72.