Azobenzene block copolymers

Tong X, Wang G, Soldera A, Zhao Y. (2005) How can azobenzene block copolymer vesicles be dissociated and reformed by light J Phys Chem B 109 20281-20287... 

HOW TO DESIGN AZOBENZENE BLOCK COPOLYMERS FOR LIGHT-CONTROLLABLE MICELLES ... 

REVERSIBLE DISSOCIATION AND FORMATION OF AZOBENZENE BLOCK COPOLYMER MICELLES... 

Holographic Gratings and Data Storage in Azobenzene-Containing Block Copolymers and Molecular Glasses... 

Block copolymers with liquid crystalline side chains were investigated for the first time by Adams and Gronski in 1989 [60], A polymeranalogous reaction was used to attach the mesogenic side-groups to one of the blocks. In a similar way, block copolymers with azobenzene chromophores were synthesized by Ober et al. [43, 44], In the scope of this review the synthesis of azobenzene-containing block... 

Fig. 4 General synthetic strategy to obtain block copolymers with azobenzene-containing side-groups via polymeranalogous reaction (open circles) protected functional groups, (filled circles) functional groups, (rectangles) azobenzene chromophore units...

Subsequently the polybutadiene segment was functionalized by quantitatively converting the olefin double bonds of the 1,2-polybutadiene block via a hydroboration reaction to hydroxyl functions. In the last step various azobenzene-chromophores were attached via a polymeranalogous reaction. The synthesis and characterization as well as photophysical aspects of block copolymers based on an amorphous polystyrene block and a functionalized 1,2-polybutadiene block... 

Fig. 6 DSC curves of cyanoazobenzene-containing block copolymers la-d with different weight fraction of the azobenzene block. Second heating curves at a rate of 10 K min- 1 are shown...

Azobenzene-functionalized AB block copolymer systems are not limited to polystyrene-poly-1,2-butadiene-based block copolymers. In addition, we have prepared similar AB block copolymers, which are based on an amorphous PMMA matrix block and an azobenzene-functionalized PHEMA block [66] and on a PS matrix block and a functionalized PHEMA block [67],... 

Fig. 27 Stability of volume gratings in thin films of the statistical copolymer 6 and block copolymer 7 with methoxy-azobenzene side-groups...

It was demonstrated above that both the value and the stability of the refractive index modulation are far better for block copolymers than for statistical copolymers with comparable azobenzene content. But the influence of the morphology and the domain size on the refractive index modulation remains unclear. To investigate this we chose a block copolymer series with three different morphologies lamellar, cylindrical, and spherical. In Fig. 28 the growth and decay for different morphologies of the block copolymers 10 (Afn 45,900gmoP1 azobenzene content 31 wt%) and 11 (Mn 42,400gmon1 azobenzene content 25 wt%), which are based on a PMMA-PHEMA backbone, are shown [66, 113]. Both block copolymers exhibit a similar... 

Fig. 28 Growth and short-term stability of the normalized photoinduced birfringence relating to the azobenzene content in PMMA-based block copolymer films with a lamellar (azobenzene content 31.6 wt%), cylindrical (23 wt%), and spherical (7.9 wt%) morphology. Writing time 3,600 s, writing wavelength 532 nm, reading wavelength 630 nm...

Influence of Azobenzene Side-Groups in Block Copolymers... 

Table 5 Characteristic properties of block copolymers with different azobenzene side-groups...

The refractive index modulation of the block copolymer lb carrying cyano-azobenzene side-groups is more than twice that of the methoxy-substituted block copolymer 14. In addition, lb exhibits a much higher sensitivity than 14. This is just a consequence of (7), in which the sensitivity increases with the refractive index modulation. Furthermore, 14 exhibits a continuous decay after the writing laser is turned off, similar to that shown in Fig. 27. Block copolymer lb, in contrast, even shows an increase by 15% within a few hours, and the refractive index modulation is stable for years. In this case, the so-called post-development is not due to a different morphology as discussed above. Rather, the liquid crystalline character of the... 

Dynamic Relaxation Processes in Block Copolymers with Non-liquid Crystalline Azobenzene Side-Groups... 

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