Synthesis, characterization and photoinduction of optical anisotropy in liquid crystalline diblock azo‐copolymers

Abstract

Diblock copolymers with polymethyl methacrylate and side chain liquid crystalline (LC) azopolymethacrylate blocks were synthesized by atom transfer radical polymerization (ATRP). The azobenzene content in these copolymers ranges from 52 to 7 wt %. For an azo content down to 20% they exhibit a LC behavior similar to that of the azo homopolymers. Thin films of these copolymers were characterized by transmission electron microscopy (TEM). A lamellar nanostructure was observed for azo content down to 20 wt %, while no structure is observed for the copolymer with a 7% azo content. The optical anisotropy induced in these films by illumination with linearly polarized 488 nm light was studied and the results compared with those of the azo homopolymer and of a random copolymer with a similar composition. The formation of azo aggregates inside the azo blocks is strongly reduced in going from the homopolymer to the copolymers. Photoinduced azo orientation perpendicular to the 488 nm light polarization was found in all the polymers. The orientational order parameter is very similar in the homopolymer and in the block copolymers with an azo content down to 20 wt %, while it is much lower in the random copolymer and in the 7 wt %. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1899–1910, 2007

Pulsed recording of anisotropy and holographic polarization gratings in azo-polymethacrylates with different molecular architectures

“…The random copolymer and terpolymer ͑ran-PMMA-Azo20 and TER20 respectively͒ were synthesized by conventional free radical polymerization, while the block copolymer PMMA-Azo20 was synthesized by atom transfer radical polymerization, according to the method published elsewhere. 25 The structure, nomenclature, and composition of the polymers are given in Fig. 1, while thermal properties, molecular weights, and polydispersity are summarized in Table I.…”

“…These drawbacks have already been identified by several authors and different strategies specially focused on the material design have been explored, trying to obtain thick and transparent films while keeping stability and large refractive index modulation. [19][20][21][22][23][24][25][26] Ikeda and co-workers have studied the recording of anisotropy and holographic gratings using cw lasers in statistical terpolymers containing a͒ azobenzene units together with transparent methyl methacrylate ͑MMA͒ and mesogenic transparent moieties, either biphenyl or tolane in the side chain. 19,20 Linearly polarized light acts on the azobenzene units orienting them perpendicular to the polarization direction.…”

“…The recording of stable anisotropy and holographic gratings in these block copolymer materials have been accomplished by several groups using cw light sources. [21][22][23][24][25][26] Recording using short light pulses ͑in the range of nanoseconds to hundreds of femtoseconds͒ has also been demonstrated to be of relevance for optical applications. [27][28][29][30][31][32][33][34][35][36][37][38] In particular, the use of 532 nm lasers of few nanosecond pulse duration has shown to be effective in the recording of optical anisotropy and holographic gratings.…”

Highly ordered nanoporous thin films by blending of PSt‐b‐PMMA block copolymers and PEO additives as structure directing agents

“…The block polymers were characterized by size exclusion chromatography (SEC) and by 1 H, 13 C NMR and IR spectroscopy. Linear PEO homopolymers with molecular weights M n of 4.0 and 10.0 kg/mol were purchased from Polymer source Inc., and are denoted EO-H4 and EO-H10, respectively.…”

“…envisaged for these materials. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] It is now well established that the structural characteristics of block copolymer thin films can be controlled by manipulation of molecular weight, block volume fraction, and the interaction parameter, v. 1,4,5 In turn the orientation of the block domains in thin films is governed by boundary conditions such as commensurability and interfacial interaction between blocks and substrates. 1,4,5 In controlling the orientation of block copolymers in thin films, several strategies have been employed including surface modification, [17][18][19][20] solvent annealing, 21 electric fields, 22 graphoepitaxy, 23 chemical prepatterning, 24,25 shear, 26 etc.…”