Lyotropic Phases Formed by “Molecular Bottlebrushes”

Abstract

The polymerization of macromonomers (that is, end-functionalized oligomers. Scheme 1) has been a matter of extensive research in order to prepare well-defined comblike polymers. ['] 10-50 for most of the samples, and accordingly, such polymers should form liquid-crystalline phases.Here we report on X-ray scattering measurements of the polymacromonomers in toluene performed at the synchroton source in Tsukuba, Japan. which indeed show the formation of lyotropic phases, probably nematic, in semi-concentrated solution. The investigated polymacromonomer sample had a molar mass of M , = (2.2.10') gmol-' corresponding to a contour length L, = 1400 8,. The polydispersity index determined by gel permeation chromatography (GPC) was M,/M, z 1.5, and the ' the scattering angle) for polyinacromonomer concentrations 0.2 2 c 2 30% (w/w). In the dilute regime c < 0.5 YO the form factor P(4) of a single chain is measured: the intensity is seen to decrease monotonically with increasing 4. However, the qScheme 1. Reaction scheme for the preparation of the macromonomers.However, the homopolymerization of macromonomers did not yield degrees of polymerization significantly exceeding the length of a macromonomer itself, unless copolymerized with conventional small monomers. A major breakthrough was achieved by Tsukahara et al., who in a radical mechanism homopolymerized anionically prepared oligostyrenes with molar masses between lo3 and lo4 gmol-' that were end-functionalized with methacryloyl groups and obtained degrees of polymerization (weight average) P, of up to 1000.[21 Recent structure characterization of such long-chain polymacromonomers revealed that the main chain exhibits an almost rodlike conformation as measured by the Kuhn statistical segment length ofApparently. the extended structure of the polymethacrylate (PMA) main chain is caused by the strong overcrowding of the oligostyrene side chains, which are only separated by a contour distance 1 = 2.5 8, at the polymer backbone.Also, because of the length of the side chains, the diameter or cross-section of this curved cylindrical macromolecule or "bot- Particularly at the highest measured concentration of 31.5 %, the width of the scattering peak narrows drastically. The scattering peaks observed at higher concentrations cannot be explained by single-particle scattering but rather reflect the interparticle structure factor S(4) originating from the intermolecular order of the molecules.On application of Bragg's relation, a mean distance dB between the scattering planes (100) of hexagonal order is obtained from the scattering peak at q,,, [Eq. (a)]. The mean par-ticle distance d2 is then derived from Equation(b). In order to

Structure, function, self-assembly, and applications of bottlebrush copolymers

“…Early studies implemented free radical polymerization, but macromonomer conversion was low (30 -80%) 6,[24][25][26] . A series of bottlebrush polymers were produced using this technique and studied in solution [27][28][29][30][31] . Ring opening metathesis polymerization (ROMP) of norbornenyl macromonomers has been shown to be an effective grafting-through synthesis strategy, such as the example shown in Fig.…”

Comb Copolymer Brush with Chemically Different Side Chains

“…21 The experimental characterization of the comb copolymer brush conformation in dilute solution is a highly nontrivial issue. It was achieved recently by Schmidt and co-workers [21][22][23][24][25][26][27][28] using a combination of light scattering experiments and theoretical modeling. Since the high grafting density is supposed to lead to a stiff molecular structure, the modeling has been based on the Kratky-Porod wormlike chain model.…”

Architecture of Multi-Component Copolymer Brushes: Synthesis, Solution Properties and Application for Nanodevices

“…Since both the degree of polymerization (DP n ) and the length of branches are varied, poly(macromonomer)s, often so-called ''polymer brushes'', are interesting models for the study of branched polymers. [1][2][3][4][5][6][7][8][9] More recently, we have systematically investigated the architecture of multi-component copolymer brushes. Figure 1 shows the illustration of three types of multi-component copolymer brushes.…”