Photoactive Thermoplastic Elastomers of Azobenzene-Containing Triblock Copolymers Prepared through Atom Transfer Radical Polymerization

• Published in: Macromolecules Vol. 37; no. 19; pp. 7097 - 7104
• Main Authors: Cui, Li, Tong, Xia, Yan, Xiaohu, Liu, Guojun, Zhao, Yue
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 21.09.2004
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Polymers with particular properties; Preparation, kinetics, thermodynamics, mechanism and catalysts; Photoisomerization; Atom transfer polymerization; Thermotropic state; Mechanical properties; Elasticity; Thermoplastic rubber; Cis trans isomerization; Experimental study; Butyl acrylate copolymer; Phase transitions; Diffraction grating; Azo compound; Monodispersed polymer; Triblock copolymer; Side chain; Molecular orientation; Order parameter; Liquid crystal polymers; Preparation; Radiation effect; Light sensitive copolymer; Oriented copolymer; Methacrylate copolymer; Photolithography
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma048995j

Atom transfer radical polymerization (ATRP) was used to prepare a new series of ABA triblock copolymers that are photoactive thermoplastic elastomers. The samples synthesized have the same rubbery midblock of poly(n-butyl acrylate) (PnBA) but differ in the degree of polymerization of the end blocks of a methacrylate-based azobenzene-containing side-chain liquid crystalline polymer (Azo-SCLCP). The coupling between elasticity, liquid crystallinity and photoactivity imparts interesting features to this type of thermoplastic elastomers. When the solution-cast film is stretched at T > T g of the Azo-SCLCP whose microdomains act as physical cross-links, in contrast to conventional thermoplastic elastomers (such as styrene−butadiene−styrene triblock copolymer) that lose the elasticity, liquid crystalline microdomains can support part of the elastic extension of PnBA chains and, in the same time, deform to result in a long-range orientation of azobenzene mesogens. The liquid crystal orientation is retained in the relaxed film at T < T g, which creates a thermoplastic elastomer whose glassy microdomains contain oriented azobenzene mesogens. Moreover, the reversible trans−cis photoisomerization of the azobenzene chromophore can be used to modulate the mechanically induced orientation.