Synthesis of novel helical poly(N-propargylamides) containing azobenzene pendant groups and effects of substitution groups on azobenzene on the stability of helix. (May 2015)

• Record Type: Journal Article
• Authors: Ren, Xiao; Li, Shujing; Zhang, Junmei; Zhang, Qingzhong; Huang, Wei
• Is Part Of: European polymer journal. Volume 66(2015:May)
• Page Start: 198
• Page End: 206
• Publication Date: 2015-05
• Subjects: Poly(N-propargylamide) -- Helical structure -- Azobenzene -- Stability -- Dipole; Polymers -- Periodicals; Polymerization -- Periodicals; Polymères -- Périodiques; Polymérisation -- Périodiques; Polymerization; Polymers; Periodicals; Electronic journals; 547.705
• DOI: 10.1016/j.eurpolymj.2015.01.050
• Languages: English
• ISSNs: 0014-3057

Abstract

Graphical abstract: Highlights: A series of novel stable helical poly( N -propargylamides) were prepared. Poly(V1–3 ) kept stable helices upon the temperature, solvents and UV irradiation. The strengthened hydrogen bonding increased the helical stability. Steric repulsion between bulky substituted azobenzene groups stabilized the helix. Electrostatic interaction between azobenzene dipoles stabilized the helix. Abstract: A series of novel N -propargylamides bearing substituted azobenzene pendant groups (RC6 H4 NNC6 H4 CONHCH(CH3 )CONHCH2 CCH, R = CH3 CH2 N(CH2 )2 OOC(CH2 )3 CH3 (V1 ), R = CH3 CH2 N(CH2 )2 OOCCH2 NHCOCH3 (V2 ), R = H (V3 )) were synthesized and polymerized with [Rh(nbd)Cl]2 as a catalyst to obtain the corresponding polymers (Poly(V1 – 3 ) ). The azobenzene chromophores in the side chains ofPoly(V1, 2 ) contained bulky electron-donating substituents, while the azobenzene inPoly(V3 ) did not bear this kind of substituent. The introduction of substituted azobenzene chromophores into the side chains of poly( N -propargylamides) was found to increase the hydrogen bond strength, steric repulsion and electrostatic interactions between the neighboring side chains. These factors worked together to improve the helical stability of poly( N -propargylamides). The solubility of these poly( N -propargylamides) was increased by introducing substituents into the azobenzene chromophores. CD and UV–vis spectra showed that all the poly( N -propargylamides) took the helical structures with predominantly one-handed screw sense, which were tight helices. Furthermore, the unsubstituted azobenzene groups in the side chains ofPoly(V3 ) also arranged to form the helical conformation. The helical structures ofPoly(V1 – 3 ) remained stable at various temperatures (5–60 °C).Poly(V1, 2 ) exhibited good helicity in polar solvent, which indicated that the bulky substituents, electrostatic and steric repulsion between the adjacent side chains lessened the effect of polar solvent on the hydrogen bonding. The main chains ofPoly(V1, 3 ) still kept helical sense after the isomerization of trans -azobenzene to the cis form upon UV irradiation. The helical array of azobenzene side chains inPoly(V3 ) experienced reversible arrangement–disarrangement upon photoirradiation.