Synthesis, Nanostructures, and Functionality of Amphiphilic Liquid Crystalline Block Copolymers with Azobenzene Moieties

Abstract

A series of liquid crystalline (LC) homopolymers of poly{11-[4-(4-butylphenylazo)phenoxy]undecyl methacrylate}containing an azobenzene mesogen with different degrees of polymerization were synthesized by using the atom transfer radical polymerization (ATRP) method. The homopolymers were prepared with a range of number-average molecular weights from 6100 to 23 500 with narrow polydispersities of less than 1.17. Thermal investigation showed that the homopolymers exhibit monolayer smectic A, smectic C, and an unknown smectic X phases. The transition temperatures increase slightly with the increase of the molecular weights and level off at around 21 500. Novel amphiphilic LC-coil diblock copolymers with a defined length of a flexible poly(ethylene glycol) segment as the hydrophilic coil were also prepared by the ATRP method. The LC-coil diblock copolymers exhibit narrow polydispersities of less than 1.11. Morphologies of the thin films of the block copolymers were investigated by using transmission electron microscopy (TEM). Microphase separation with small size in the range of 10−20 nm (nanoseparated structures) was observed. Different photophysical and photochemical behaviors were observed between annealed homopolymer and block copolymer films, which is thought to be caused by the formation of nanostructures of the block copolymers.

Single-molecule electroluminescence and photoluminescence of polyfluorene unveils the photophysics behind the green emission band

“…1c) and atomic force microscopy ( Fig. 1d) of a 70 nm thick BC film doped with on average 1 BDOH-PF chain per cylinder reveal average cylinder diameter of 13 nm and cylinder-to-cylinder distance of 33 nm, as expected for this type of BC 30 . PL spectra of BDOH-PF in the BC are almost identical to those of BDOH-PF dispersed in a PEO homopolymer film (Fig.…”

“…1a). The amphiphilic BC consists of a PEO block and of a hydrophobic block of polymethacrylate with chalcone mesogen in the side chains (PMA(Chal)) 30 . An annealed BC film forms hexagonally arranged PEO cylinders that span continuously the whole-film thickness.…”

“…The M n was 9,950, M w was 18,600 and the polydispersity index was 1.87. The BC PEO m -b-PMA(Chal) n and the corresponding homopolymers PEO 114 and PMA(Chal) 50 were synthesized mainly using standard methods as described before 30 . BDOH-PF-doped BC films were facbricated by first preparing a 1 wt% chloroform solution of the BC into which small amount of BDOH-PF was added to the final concentrations of 2 Â 10 À 8 or 2 Â 10 À 10 M (corresponding to the respective densities of 1 chain per cylinder or 1 chain per 100 cylinders in the phase-separated film).…”

Optical and Physical Applications of Photocontrollable Materials: Azobenzene-Containing and Liquid Crystalline Polymers

“…Such a film consisting of well-organized PEO domains can be utilized as a nano-template. Iyoda and coworkers attained uniform alignment in an azobenzene/PEO liquid crystalline diblock copolymer by thermal treatment [173]. The array of hexagonally arranged PEO cylinders is induced by homeotropic alignment of the azobenzene mesogens in the smectic phase.…”

Thermodynamics and Thermokinetics to Model Phase Transitions of Polymers over Extended Temperature and Pressure Ranges Under Various Hydrostatic Fluids

“…Beautiful illustrations are available in the literature. To cite a few, the rod-like eutectic structure is observed in a dual-phase pattern, namely for metallic with ceramic, and for polymeric (De Rosa et al, 2000;Park et al, 2003) systems like nanometric length scale of hexagonal structure of poly(ethylene-oxide) PEO cylinders in amphiphilic diblock copolymer PEO m -b-PMA(Az) n with azobenzene part PMA(Az) (Tian et al, 2002). Dendritic patterns are embellished with images like snowflake ice dendrites from undercooled water (Kobayashi, 1993) and primary solidified phase in most metallic alloys (e.g., steel, industrial alloys) (Trivedi & Laorchan, 1988a-b), and even dendrites in polymer blends (Ferreiro et al, 2002a) like PEO polymer dendrites formed under cooling PEO/polymethyl methacrylate PMMA blend (Gránásy et al, 2003;Okerberg et al, 2008).…”