Phase Behavior and Photoresponse of Azobenzene-Containing Polystyrene-block-poly(n-butyl methacrylate) Block Copolymers

Abstract

It is well-known that polystyrene-block-poly(n-butyl methacrylate) (PS-b-PnBMA) block copolymers (BCPs) exhibit an hourglass-shaped phase diagram, resulting from the simultaneous appearance of an upper order-to-disorder transition (UODT) and a lower disorder-to-order transition (LDOT). Here, the phase behavior of three azobenzene-containing PS-b-PnBMA BCPs was investigated by small-angle neutron scattering (SANS). As to their molecular weights of M n = 24 000, 40 000, and 47 000, the three copolymers are designated as Azo24k, Azo40k, and Azo47k, respectively. Temperature-dependent SANS data show that Azo24k and Azo40k BCPs are closer to their corresponding LDOT and UODT, respectively, while Azo47k BCP locates in the middle of temperature interval between UODT and LDOT. This indicates that after incorporating azobenzene functionalities into PnBMA blocks, the azobenzene-containing PS-b-PnBMA BCPs still exhibit both LDOT and UODT, characteristic of the "compressibility" similar to their parent PS-b-PnBMA BCPs. After exposing the films of three azobenzene-containing PS-b-PnBMA BCPs to UV light with a wavelength of 365 nm, the photoisomerization of azobenzene produces light-induced motions and thereby gives rise to conformational increase and density variation, which can result in a significant increase in entropy. As a consequence, three disordered azobenzene-containing PS-b-PnBMA BCPs are driven toward LDOT.

Smart polymers for optical data storage

“…Of particular interest is ATRP, which has been used to prepare azobenzene BCs with poly(methylmethacrylate) (PMMA) (Yu et al, 2008) PS, (Chen et al 2011;Cui et al ., 2003), poly(n-butyl acrylate), (Deng et al , 2008) or poly(ethylene) glycol (PEG) blocks (Kadota et al , 2005;Tang et al , 2007) amongst others (see a representative example in Fig. 16.10).…”

“…The ATRP was successfully used by Matyjaszewski and co-workers to prepare well-controlled 4-cyanoazobenzenemethacrylate homopolymers and BCs with n-butyl acrylate segments under various experimental conditions. To prepare the BCs, poly(n-butyl acrylate) was grown fi rst and then used to produce the azoblock (Chen et al, 2011). The same strategy has been used by Ikeda and co-workers, where a bromo-terminated PMMA was used as a macroinitiator to obtain diblock copolymers, diblock random copolymers incorporating 4-cyanobiphenyl moieties in the photoaddressable block (Yu et al, 2008), or triblock copolymers where the azoblock was the terminal block (Yu et al ., 2007).…”

“…In addition, due to the size of these domains, which are usually much smaller than the recording wavelength, light scattering can be signifi cantly reduced in these materials in comparison to their homopolymer counterparts. Most of the reported azobenzene BCs have a non-absorbing block that is either PMMA (Forc é n et al ., 2007a;Gimeno et al ., 2009) or PS (Chen et al ., 2011;H ä ckel et al ., 2005a). The photoresponsive block can be composed of an azobenzene side-chain polymer or a random copolymer containing other mesogenic group s (Forc é n et al .…”

Hierarchical self-assembly, photo-responsive phase behavior and variable tensile property of azobenzene-containing ABA triblock copolymers

“…45,47 The photoresponsive property of the azobenzene moiety affords good light-controllability to the azobenzene-containing polymers. [48][49][50] For example, in the azobenzene-containing BCPs the photoisomerization of azobenzene can lead to the change in microphase separation of the BCPs in the bulk 12,51,52 and orientation of the microphaseseparated domains in the thin lm. 12,53 The trans-cis photoisomerization of the azobenzene moiety may also result in the macroscopic contraction in size.…”

Self-assembly and photo-responsive behavior of novel ABC2-type block copolymers containing azobenzene moieties

“…In recent years, azobenzene-containing polymers have attracted considerable attention due to their photo-responsive properties and potential applications. [1][2][3][4][5][6] One of the most important properties of azobenzene-containing polymers is light-induced transcis isomerization of azobenzene moieties. Triggered by this property, azobenzene-containing polymers can show various photo-responsive properties, such as reversible solubility, 7 surface free energy changes 8,9 and photodeformation.…”