Azo polymers for reversible optical storage. 11 poly {4,4′-(1-Methylethylidene)Bisphenylene 3-[4[(4-Nitrophenylazo)Phenyl]-3-Aza-Pentanedioate}

Dual Light- and pH-Responsive Composite of Polyazo-Derivative Grafted Cellulose Nanocrystals

As a type of functional group, azo-derivatives are commonly used to synthesize responsive materials. Cellulose nanocrystals (CNCs), prepared by acid hydrolysis of cotton, were dewatered and reacted with 2-bromoisobuturyl bromide to form a macro-initiator, which grafted 6-[4-(4-methoxyphenyl-azo) phenoxy] hexyl methacrylate (MMAZO) via atom transfer radical polymerization. The successful grafting was supported by Fourier transform infrared spectroscopy (FT-IR) and Solid magnetic resonance carbon spectrum (MAS 13C-NMR). The morphology and surface composition of the poly{6-[4-(4-methoxyphenylazo) phenoxy] hexyl methacrylate} (PMMAZO)-grafted CNCs were confirmed with Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The grafting rate on the macro-initiator of CNCs was over 870%, and the polydispersities of branched polymers were narrow. The crystal structure of CNCs did not change after grafting, as determined by X-ray diffraction (XRD). The polymer PMMAZO improved the thermal stability of cellulose nanocrystals, as shown by thermogravimetry analysis (TGA). Then the PMMAZO-grafted CNCs were mixed with polyurethane and casted to form a composite film. The film showed a significant light and pH response, which may be suitable for visual acid-alkali measurement and reversible optical storage.

Synthesis and characterization of new photoswitchable azobenzene-containing poly(ε-caprolactones)

A novel and efficient strategy in obtaining mono- and bi-armed azobenzene-containing poly(ε-caprolactone)s is described, starting from a commercially available azobenzene dye.

Long-term stability at high temperatures for birefringence in PAZO/PAH layer-by-layer films

Optical memories with long-term stability at high temperatures have long been pursued in azopolymers with photoinduced birefringence. In this study, we show that the residual birefringence in layer-by-layer (LbL) films made with poly[1-[4-(3-carboxy-4 hydroxyphenylazo)benzene sulfonamido]-1,2-ethanediyl, sodium salt] (PAZO) alternated with poly(allylamine hydrochloride) (PAH) can be tuned by varying the extent of electrostatic interactions with film fabrication at different pHs for PAH. The dynamics of both writing and relaxation processes could be explained with a two-stage mechanism involving the orientation of the chromophores per se and the chain movement. Upon calculating the activation energies for these processes, we demonstrate semiquantitatively that reduced electrostatic interactions in films prepared at higher pH, for which PAH is less charged, are responsible for the longer stability at high temperatures. This is attributed to orientation of PAZO chromophores via cooperative aggregation, where the presence of counterions hindered relaxation.

Photoinduced birefringence in copolymers containing Disperse Red 1 and styrene

A series of copolymers of 4'-[[[2-(methacryloyloxy)ethyl]ethyl]amino]-4-nitroazobenzene (DR1M) and an optically "inert" styrene comonomer were tested for photoinduced birefringence. The level of saturated birefringence increased linearly with the content of DR1M in the copolymer. The birefringence per mole of azo chromophore was constant along the copolymer series.Key words: azobenzene, photoinduced birefringence, copolymers, trans-cis isomerization.