Molecular Technology, Volume 4

Synthesis Innovation

Hisashi Yamamoto, Takashi Kato, Hisashi Yamamoto, Takashi Kato

• Publisher: Wiley-VCH
• Year: 2019
• Print ISBN: 9783527345885
• eBook ISBN: 9783527820436
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Chemistry
• Index: Chemistry

Edited by foremost leaders in chemical research together with a number of distinguished international authors, this fourth volume summarizes the most important and promising recent developments in synthesis, polymer chemistry and supramolecular chemistry.

Interdisciplinary and application-oriented, this ready reference focuses on innovative methods, covering new developments in catalysis, synthesis, polymers and more.

1
Polymerization‐Induced Self‐assembly of Block Copolymer Nano‐objects via Green RAFT Polymerization

Shinji Sugihara

University of Fukui, Graduate School of Engineering, Department of Applied Chemistry and Biotechnology, 3‐9‐1 Bunkyo, Fukui, 910‐8507, Japan

1.1 Introduction

Many biomolecules have specific three‐dimensional structures in water or hydrophobic environments, and form higher order structures with high functions. To construct a highly functionalized and higher order structure with a synthetic polymer, it is necessary to examine the fundamental formulation to control the polymer's primary structure and to build the polymers up into a higher order structure. From this point of view, this chapter focuses on block copolymer synthesis as a molecular technology for self‐organization. The key technology is in situ “polymerization‐induced self‐assembly (PISA).”

1.2 Block Copolymer Solution

Self‐assembly of AB diblock, ABA, or ABC triblock copolymers to form a variety of macromolecular nanostructures is well known in both the solid state and in dilute solutions, with various prominent functions stemming from the structure [1–21]. In particular, amphiphilic AB diblock copolymers have been demonstrated to form a variety of self‐assembled aggregate structures in dilute solutions, where the solvent preferentially solvates one of the blocks. Thus, the basic driving force for solution self‐assembly is the solvophobic effect (hydrophobic effect in aqueous solution). These are well documented in other reviews [ 1–5]. For the amphiphilic AB diblock copolymer in a block‐selective solvent, the precise nanostructure, i.e. morphology, is primarily a result of the inherent molecular curvature described by its mean curvature H and its Gaussian curvature K, which are given by the two radii of curvatures R₁ and R₂ in Figure 1.1. The curvature is related to the surfactant packing parameter, P, which is given by Eq. (1.1). The value of P depends on the relative core‐block volume (v), the effective interfacial area (a₀) at the core–shell/solvent interface, and the chain length normal to the surface per molecule (l₀).

1.1

Figure 1.1 Various self‐assemblies formed by solvophilic block copolymers in a block‐selective solvent. The type of structure formed is due to the inherent curvature of the molecule, which can be estimated through calculation of its dimensionless packing parameter, P.

The regions of spherical micelles are favored when P ≤ 0.33, cylindrical micelles are produced when 0.33 < P ≤ 0.50, and vesicles are formed when 0.50 < P ≤ 1.00. Although vesicles are flexible bilayer aggregates, the planar bilayer of lamellae is ideally favored when P = 1. This concept was originally introduced by Israelachvili et al. [22,23] to explain self‐assembly of small‐molecule surfactants, and was later extended to include diblock copolymer self‐assembly by Antonietti and Förster [24].

In practice, morphology is controlled by various factors, especially for small‐molecule amphiphiles. Assemblies such as spherical micelles, hexagonals, cubes, and lamellar lyotropic crystallines are highly dynamic with rapid exchange of molecules between micelles and the unimer state in solution. Thus, as shown in Figure 1.2, the packing geometry can be tuned by simply adjusting the surfactant concentration with the same solvent properties, i.e. without additives and at a constant temperature. Figure 1.2 shows an ideal phase sequence, which is only a very generalized picture, and the sequence may be different for some amphiphiles. However, this rapid exchange of molecules is very important to determine the structure and morphology of amphiphilic self‐assembled aggregates [4 23–25].

Figure 1.2 The “ideal” sequence of phases from L₁ to H_I to L_α observed upon increasing amphiphile concentration, in a binary small‐molecular amphiphile–solvent system (ergodic system). Intermediate phases (a and b) are sometimes observed. The normal micellar structure is termed the L₁ phase. At higher concentrations, micelles can fill space efficiently to form a cubic phase by packing (a). Upon increasing the concentration further, the micelles change from spherical to rod‐like ones. The rod‐like micelles then pack into a hexagonal (H_I) phase. The H_I phase sometimes changes to a bicontinuous cubic or mesh structure phase (b), which is characterized by nonzero mean curvature and negative Gaussian curvature. The phase then changes to bilayers, which tend to stack into a lamellar phase (L_α). Lamellar phases can be found in different phase states including lamellar crystalline, lamellar gel, and lamellar fluid. When the solvent becomes the minority phase, inverse structures are formed such as the inverse hexagonal phase (H_II), inverse micellar liquid phase (L₂), and intermediates such as the inverse bicontinuous phase (c), and inverse micellar cubic phase (d).

For many macromolecular amphiphiles, in contrast to small‐molecule amphiphiles, the rate of exchan...

Table of contents

• Cover
• Table of Contents
• Foreword by Dr. Hamaguchi
• Foreword by Dr. Noyori
• Preface
• 1 Polymerization‐Induced Self‐assembly of Block Copolymer Nano‐objects via Green RAFT Polymerization
• 2 Chemical Functionalization of Graphitic Nanocarbons
• 3 Synthetic Methods Using Interactions Between Sustainable Iron Reagents and Functionalized Carbon–Carbon Multiple Bonds
• 4 Molecular Technology for Switch and Amplification of Chirality in Asymmetric Catalysis Using a Helically Dynamic Macromolecular Scaffold as a Source of Chirality
• 5 Cooperative Double Activation Metal/Metal and Metal/Organic Catalysis Enabling Challenging Organic Reactions
• 6 Siloxane‐Based Building Blocks for Molecular Technology
• 7 Organic Molecular Catalysts in Radical Chemistry: Challenges Toward Selective Transformations
• 8 Coordination Molecular Technology
• 9 Molecular Technology for Synthesis of Versatile Copolymers via Multiple Polymerization Mechanisms
• 10 Self‐assembled Monolayers from Carbon‐Based Ligands on Metal Surfaces
• 11 Supramolecular Web and Application for Chiroptical Functionalization of Polymer
• 12 Conformational Analysis of Organic Molecules with Single‐Molecule Atomic‐Resolution Real‐Time Transmission Electron Microscopy (SMART‐TEM) Imaging
• 13 Designer Molecules Toward Sequence‐Controlled Polymers via Chain‐Growth Propagation Mechanism
• 14 Hairy Particles Synthesized by Surface‐Initiated Living Radical Polymerization
• Index
• End User License Agreement