Effect of the terminal substituent of azobenzene on the properties of ABA triblock copolymers via atom transfer radical polymerization

Abstract

The effect of the terminal substituent of azobenzene on the properties of ABA triblock copolymers was investigated. For this study, three kinds of azobenzene-containing monomers with different terminal substituents-6-[4-(4-methoxyphenylazo)phenoxy] hexyl methacrylate, 6-[4-(4-ethoxyphenylazo)phenoxy]hexyl methacrylate, and 6-[4-(4nitrophenylazo)phenoxy]hexyl methacrylate-were used to synthesize ABA triblock copolymers PMMAzo 25 -PEG 13 -PMMAzo 25 /PMMAzo 12 -PEG 13 -PMMAzo 12 , PEMAzo 14 -PEG 13 -PEMAzo 14 , and PNMAzo 14 -PEG 13 -PNMAzo 14 , respectively, by atom transfer radical polymerization (PMMAzo is poly{6-[4-(4-methoxyphenylazo)phenoxy]hexyl meth-acrylate}, PEMAzo is poly{6-[4-(4-ethoxyphenylazo)phenoxy]hexyl methacrylate}, and PNMAzo is poly{6-[4-(4-nitrophenylazo)phenoxy]hexyl methacrylate}). These copolymers were characterized with 1 H NMR spectroscopy and gel permeation chromatography and exhibited controlled molecular weights and narrow molecular weight distributions. Differential scanning calorimetry and polarizing optical microscopy showed that these copolymers had mesophases. PMMAzo 25 -PEG 13 -PMMAzo 25 and PMMAzo 12 -PEG 13 -PMMAzo 12 had a smectic mesophase and a nematic mesophase, whereas both PEMAzo 14 -PEG 13 -PEMAzo 14 and PNMAzo 14 -PEG 13 -PNMAzo 14 had a nematic mesophase. This demonstrated that the liquid-crystalline properties of these copolymers highly depended on the terminal substituent of azobenzene. The photoresponsive behavior of these copolymers was also investigated in tetrahydrofuran solutions, and the influence of the terminal substituents attached to azobenzene was studied. V V C 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5190-5198, 2007

Transition Metal-Catalyzed Living Radical Polymerization: Toward Perfection in Catalysis and Precision Polymer Synthesis

“…Figure shows functional monomers (FM- 79 to FM- 99 ), − all acrylates and methacrylates, thus far employed for liquid crystalline and optically active polymers via metal-mediated living radical polymerization with copper salts (CuBr or CuCl) and multidentate aliphatic amine ligands (PMDETA or HMTETA). Though monomer conversion is invariably at most about 50%, polymer molecular weights were generally controlled with M w / M n < 1.3, independent of the pendants structures.…”

Photoresponsive side-chain liquid crystalline polymers with amide group-substituted azobenzene mesogens: effects of hydrogen bonding, flexible spacers, and terminal tails

“…A variety of azo-containing sidechain LCPs with different molecular structures have been prepared via various polymerization approaches. 1,3,4,6,7,[12][13][14][15][16][17][18][19][20][21][22] Systematic studies on the structure-property relationship of the azo-containing side-chain LCPs have revealed that both their phase transition behaviors and photoresponsive properties are strongly dependent on their polymer backbones, 13,14 the azo mesogens, [15][16][17][18] and the length of the flexible spacers. [19][20][21][22] Among these influencing factors, the molecular structures of the azo mesogens, especially the terminal substitutent of the azo groups, have been recognized as one of the most important primary factors influencing the properties of the azo polymers because the azo groups act as both the mesogenic and photoresponsive units and their substituents can have significant influence on the dipole moment of the azo chromophores and thus their phase transition and photoresponsive behaviors.…”

“…[19][20][21][22] Among these influencing factors, the molecular structures of the azo mesogens, especially the terminal substitutent of the azo groups, have been recognized as one of the most important primary factors influencing the properties of the azo polymers because the azo groups act as both the mesogenic and photoresponsive units and their substituents can have significant influence on the dipole moment of the azo chromophores and thus their phase transition and photoresponsive behaviors. [15][16][17][18] Therefore, many side-chain LCPs bearing pendant azo mesogens with various substituents such as hydrogen, 23 alkyl, 24,25 perfluoroalkyl, 17 alkyloxy, 15,26,27 chiral alkyloxy, 21,28 nitro, 19,29,30 cyano, 31,32 carboxyl, 33 cinnamoyl, 34,35 and N-hydroxysuccinimide carboxylate groups 36 have been developed for different purposes.…”

Photoresponsive side-chain liquid crystalline polymers with an easily cross-linkable azobenzene mesogen

“…[8][9][10] Among them, the combshaped side-chain LCPs with pendant azo groups have been the most extensively investigated materials up to now. 2,[4][5][6][7] To be suited for different application purposes, many sidechain LCPs bearing pendant azo mesogens with different substituents such as hydrogen, 11,12 alkyl, 13,14 perfluoroalkyl, 15 alkyloxy, [16][17][18] chiral alkyloxy, 19,20 nitro, [21][22][23] cyano, 24,25 carboxyl 26 and cinnamoyl group 27,28 have been developed. Among them, the side-chain LCPs bearing azo mesogens with reactive substituting groups are particularly interesting because of their combined properties of liquid crystallinity, photoresponsivity and reactivity.…”