On the thread-like morphology of LC/I block copolymers in nematic solvents

Abstract

SUMMARY AB and ABA block copolymers are synthesized by direct living anionic polymerization where the A-block is a liquid crystalline side chain polymer (LC-block) and the B-block is an isotropic polymer (Iblock). Similar to amphiphilic block copolymers with a "hydrophilic" water soluble segment and a "hydrophobic" water insoluble part, the LC/I block copolymers consist of the "nematophilic" LC-block that is soluble in a nematic solvent and the "nematophobic" segment that is insoluble in nematic solvents. The behaviour of these LC/I block copolymers and corresponding homopolymers is analyzed in dilute nematic solutions of low molar mass liquid crystals. The effects of varying molecular weight, chemical constitution of blocks and block length ratio are investigated. Copolymers with a high fraction of the I-block are insoluble in the nematic solvent as indicated by phase separation. Copolymers with a high fraction of the LC-block are completely soluble. If the weight fraction of the LC-block is in the range of 0.46 to 0.85, thermoreversible thread-like aggregates are formed in the nematic solvent. These thread-like aggregates have a uniform diameter of 2-3 pm and their long axis perfectly follows the director field of the nematic matrix. The formation of these structures is discussed in terms of copolymer concentration, temperature and influence of aligning surfaces. From simple geometrical packing arguments it can be assumed that these thread-like aggregates consist of bilayered vesicles. In contrast to the spherical shape of amphiphilic block copolymer vesicles in aqueous solution, the rod-like shape of vesicles in nematic solution is caused by the minimization of free elastic energy density of the nematic matrix.

ABA‐type amphiphilic triblock copolymers containing p‐ethoxy azobenzene via atom transfer radical polymerization: Synthesis, characterization, and properties

“…Most of the reported Azo‐containing polymers are synthesized by random copolymerization, mainly because of the various constraints in syntheses using living polymerization techniques 4, 13. Until now, only a few Azo‐containing polymers have been synthesized by living polymerization, such as anionic polymerization,14, 15 cationic polymerization,16 and atom transfer radical polymerization (ATRP) 12, 13, 17–23. The emergence of controlled/living radical polymerizations in the past decade have simplified the synthesis of well‐defined polymers.…”

Synthesis, self‐assembly behavior, and biological application of a new photochromic azo amphiphilic diblock copolymer

“…2. PAzoMA is known to have a smectic (S) and nematic (N) phase [17, 18]. For p(DMAEMA 79 ‐ b ‐AZOM 7 ), the glass transition was observed to occur at T g = 51°C, the liquid crystalline transition at 88°C, and the isotropic transition at 115°C.…”

Light‐Responsive Block Copolymers

“…Despite the photo-responsivity of azobenzene-containing polymers being known for a long time, [23][24][25]50,51] azobenzene moieties were initially incorporated in block copolymers only for their mesogenic properties due to their rigid rod-like structure in the trans form. [52][53][54][55][56][57] In those systems, one block contains the azobenzenes as side groups which confers a mesogenic character to the block copolymers. The other(s) sequence(s) is (are) composed of traditional coil-like chain(s).…”