Z-E isomerization of azobenzene based amphiphilic poly(urethane-urea)s: Influence on the dynamic mechanical properties and the effect of the self-assembly in solution on the isomerization kinetics. (15th March 2020)

• Record Type: Journal Article
• Authors: Paiva, Germana Maria Santos; Duarte, Luís Gustavo Teixeira Alves; Faleiros, Marcelo Meira; Atvars, Teresa Dib Zambon; Felisberti, Maria Isabel
• Is Part Of: European polymer journal. Volume 127(2020)
• Publication Date: 2020-03-15
• Subjects: Poly(urethane-urea) -- Amphiphilic -- Self-assembly -- Photoisomerization -- Dynamic mechanical properties; Polymers -- Periodicals; Polymerization -- Periodicals; Polymères -- Périodiques; Polymérisation -- Périodiques; Polymerization; Polymers; Periodicals; Electronic journals; 547.705
• DOI: 10.1016/j.eurpolymj.2020.109583
• Languages: English
• ISSNs: 0014-3057

Abstract

Graphical abstract: Amphiphilic, semicrystalline and flexible poly(urethane-urea)s (PUU) containing azo groups in the main chain are capable of self-assembly in solution, which strongly influences the kinetics of the photoisomerization, and their relaxation spectra differ for Z and E-isomers. Highlights: Amphiphilic poly(urethane-urea) (PUU) based on 4, 4́-diamine azobenzene were synthesized. PUU self-assemble in solution, which affects the azo photoisomerization. The polymers are dimensionally stable up to 150 °C, 100 °C higher than Tm. Dynamic mechanical properties of the cis- and trans-isomers are quite different. Abstract: Azobenzene containing polymers have been used in the development of materials and devices responsive to light, devices for optical storage information, with shape-changing and shape-memory capacities, surface-relief grating, holograms, etc. Poly(urethane-urea)s (PUU) based on a hydrophilic polyethylene glycol (PEG-PUU), on a hydrophobic polycaprolactone diol (PCL-PUU) polyols, and on an equimolar mixture of them (PEG/PCL-PUU), 4, 4′-diphenylmethane diisocyanate and 4, 4′-diaminoazobenzene (DAAB), as a chain extender, were synthesized by a two-step route. PUU were characterized with respect to their chemical structure, molar masses, thermal and dynamic mechanical properties, and spectroscopic properties. The kinetics of the photo- and thermal-induced isomerization were studied in DMF solutions. The isomerization rate constant was two orders of magnitude higher for DAAB compared with PUU in DMF solution, except for PEG/PCL-PUU, for which the rate constant was half the value observed for DAAB. The amphiphilic nature of the PUU resulted in aggregates in DMF and, therefore, the azo isomerization for PEG-PUU and PCL-PUU occurred in a solid-state-like environment. On the other hand, PEG/PCL-PUU presented unimers and aggregates in DMF and the isomerization of azo groups in free PUU chains was faster. The PUU were semicrystalline and thermo-mechanically stable up 150 °C due to the hydrogen bonding involving urea, urethane and ester groups. The aggregates size in DMF solution, as well as the dynamic mechanical properties of the PUU, were sensitive to photo- and thermo-induced isomerization.