Molecular Design, Synthesis, and Characterization of Liquid Crystal−Coil Diblock Copolymers with Azobenzene Side Groups

Abstract

The synthesis and characterization of a family of well-defined liquid crystal−coil (LC−coil) diblock copolymers have been carried out. The block copolymers in this study have been designed to have nearly identical molecular weight azobenzene-containing LC blocks in order to eliminate possible variations in LC behavior caused by the differences in the LC block molecular weight. Quantitative hydroboration chemistry was used to convert the pendent double bonds of an isoprene block to hydroxyl groups to which the mesogenic groups were attached via acid chloride coupling. The LC homopolymer and the block copolymers (LC volume fraction from f LC = 0.82 to f LC = 0.20) all exhibited smectic mesophases with similar clearing transition temperatures. The clearing transition enthalpies strongly depend on the block composition ratio and decrease as the LC block volume fraction decreases. Solvent-casting of a lamellar LC−coil copolymer (SICN5-66/60) resulted in an oriented bulk film in which both the axes of the mesogenic groups and the lamellar interfaces lie parallel to the film surfaces. A LC cylinder morphology was observed with a f LC = 0.22 LC-containing block (SICN5-176/55) using TEM and confirmed by SAXS measurements. This is the first observation with the LC block in a cylinder microdomain. Other morphologies (bicontinuous, LC sphere) were observed by TEM while retaining the smectic order in the LC microphase.

Understanding and controlling the morphology of styrene–isoprene side-group liquid crystalline diblock copolymers

“…The anchoring condition of the mesogen with respect to the IMDS (inter-material dividing surface) was not determined, nor was the influence of spacer length explored. The noted absence of the cylindrical LC phase, as one might expect, is specific to the system and should not be universally expected [2,15].…”

“…Work conducted collaboratively by the Ober (Cornell) and Thomas (MIT) groups has focused on both LC rodamorphous coil block copolymers [19][20][21][22][23] and amorphous side-group LC-amorphous coil block copolymers [6,15,19,20,24], as well as fluorinated side group LC copolymers [25]. The structure of the azobenzene mesogen based stryene-isoprene side-group LC diblock is shown in Fig.…”

Alignment of Self-Assembled Hierarchical Microstructure in Liquid Crystalline Diblock Copolymers Using High Magnetic Fields

“…26 The chemical structure of the diblocks is shown in Figure 1, and the molecular weights and compositions are given in Table 1. Morphologies of the bulk samples were previously determined using transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS).…”

Fabrication of Hierarchically Ordered Hybrid Structures over Multiple Length Scales via Direct Etching of Self-Organized Polyhedral Oligomeric Silsesquioxane (POSS) Functionalized Block Copolymer Films

“…25 The number-average of molecular weight (M n ) of the polystyrene precursor of PS 1200 -b-PI 94 is 125,000 in GPC measurement.…”

“…It is known that this coil-coil type block copolymer can be easily converted to a series of rod-coil type block copolymers by incorporation of a variety of rigid-rod molecules into the side chains. [25][26][27][28][29] The synthesis of polystyrene-bpolyisoprene with the POSS-modified side chains (PS-b-PIPOSS) as a silicon-containing rod-coil type block copolymer was carried out by hydrosilation of polystyrene-b-poly(1,2-ran-3,4-isoprene) with the hydrido-heptacyclopentyl substituted POSS in the presence of a catalytic amount of Pt(dvs) in toluene at …”