Synthesis of side‐chain liquid‐crystalline homopolymers and triblock copolymers with p‐methoxyazobenzene moieties and poly(ethylene glycol) as coil segments by atom transfer radical polymerization and their thermotropic phase behavior

Abstract

A series of side‐chain liquid‐crystalline (LC) homopolymers of poly[6‐(4‐methoxy‐4′‐oxy‐azobenzene) hexyl methacrylate] with different degrees of polymerization were synthesized by atom transfer radical polymerization (ATRP), which were prepared with a wide range of number‐average molecular weights from 5.1 × 103 to 20.6 × 103 with narrow polydispersities of around 1.17. Thermal investigation showed that the homopolymers exhibit two mesophases, a smectic phase, and a nematic phase, and the phase‐transition temperatures of the homopolymers increase clearly with increasing molecular weights. A series of novel LC coil triblock copolymers with narrow polydispersities was synthesized by ATRP, and their thermotropic phase behavior was investigated with differential scanning calorimetry and polarized optical microscopy. The LC coil triblocks were designed to have an LC conformation of poly[6‐(4‐methoxy‐4′‐oxy‐azobenzene) hexyl methacrylate] with a wide range of molecular weights from 3.5 × 103 to 1.7 × 104 and the coil conformation of poly(ethylene glycol) (PEG) (number‐average molecular weight: 6000 or 12,000) segment. Their characterization was investigated with 1H NMR, Fourier transform infrared spectra, and gel permeation chromatography. Triblock copolymers exhibited a crystalline phase, a smectic phase, and a nematic phase. The phase‐transition temperatures from the smectic to nematic phase and from the nematic to isotropic phase increased, and the crystallization of PEG depressed with increasing molecular weight of the LC block. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2854–2864, 2003

Branched Azobenzene Side‐Chain Liquid‐Crystalline Copolymers Obtained by Self‐Condensing ATR Copolymerization

“…grade, 99%) was purified as described. [9] All other chemicals were used as received. The azobenzene monomer, 6-(4-methoxy-azobenzene-4 0 -oxy)hexyl methacrylate (M), was prepared using the procedure described by Stewart and Imrie.…”

Photochromic Responses in Polymer Matrices

“…Both side-and main-chain azobenzene-substituted polymers with good stability, rigidity, and ease of processability involve synthetic routes either using direct polymerization of azobenzene-functionalized monomers or postfunctionalization, where the chromophores are introduced to reactive precursor polymers without harsh polymerization conditions. For side-and main-chain azobenzene polymers, imides [47], esters [48], isocyanates [49], acrylates [50], methacrylates [51], urethanes [52], ethers [53], organometallic ferrocene polymers [54], dendrimers [55], and conjugated polydiacetylenes [56] have been utilized. Selected examples of azobenzene-containing polymer repeating units of (i) side chain, (ii) epoxy, (iii) organometallic ferrocene, (iv) main chain, and (v) conjugated polydiacetlylene are illustrated in Figure 9.4.…”

Self‐Assembly and Photoresponsivity Property of Amphiphilic ABA Triblock Copolymers Containing Azobenzene Moieties in Dilute Solution

“…[9,10] Amphiphilic block copolymers containing poly-(ethylene glycol) (PEG) as the hydrophilic block and azobenzene-containing block as the hydrophobic block synthesized by ATRP have been reported. [5,[11][12][13] However, the investigation on the aggregate morphologies formed in dilute solutions and their correlation with molecular structures concerning such copolymers is still limited. Recently, Wang et al synthesized a series of amphiphilic diblock copolymers that bear azobenzene chromophores and investigated their multi-morphological aggregation in dilute solution.…”