Dual-responsive supramolecular inclusion complexes of block copolymer poly(ethylene glycol)-block-poly[(2-dimethylamino)ethyl methacrylate] with α-cyclodextrin

Inclusion Complexation between α-Cyclodextrin and Oligo(ethylene glycol) Methyl Ether Methacrylate

The preparation of inclusion complexes based on α-cyclodextrin (α-CD) and oligo(ethylene glycol) methyl ether methacrylate (OEGMA) was investigated aiming to reveal complexation particularities and thermodynamic and kinetic aspects as a function of the oligomer architecture. Small-angle X-ray scattering and isothermal titration calorimetry measurements revealed that oligomer molecular weight controls both the kinetics and thermodynamics of inclusion. Unlike linear ethylene glycol polymers, OEGMA groups possess a methacrylate group, which seems to act as a stopper, affecting their mode of complexation. Nuclear magnetic resonance spectra and relaxation measurements support the fact that methacrylate groups lie outside the α-CD ring and that a full sequential complexation of the oligomer ethylene oxide groups is not observed. These results allied to the temperature sensitivity of these oligomers and enable possible routes for chemical modifications and design of new stimuli-responsive materials.

Towards Cyclodextrin-Based Supramolecular Materials

Inclusion complexation between cyclodextrins (CDs) and various guests has been extensively investigated in supramolecular chemistry. Besides CDs, there are several important macrocyclic host families, such as crown ethers and cucurbiturils. Until now, the contribution of these other families to macromolecular self-assembly has been small compared to CDs. This chapter will focus on CDs as hosts for interaction with guest monomers to form hydrogels. CD interactions with other monomers were made possible depending on proper molecular recognition. Macroscopic molecular recognition can be categorized by three types of interactions: main chain (polyrotaxane), side chain, and sequential complexes. Utilizing CD as host molecule, polymers such as polyethers, cationic polymers, polyamines, polyesters, π-conjugated polymers, polyolefins, polyamides, polyurethanes, and inorganic polymers could interact to form inclusion complexes. This chapter will attempt to discuss these studies. Depending on the functional groups attached to the polymeric component, supramolecular formation can be altered based on the stimuli response. Introducing polymer side chains or groups that respond selectively towards external stimuli could affect the hydrogel formation. This chapter also discusses the stimuli response of such systems.

Design of a micellized α-cyclodextrin based supramolecular hydrogel system

In recent years supramolecular structures built from macrocyclic compounds have attracted tremendous interest due to the unique properties derived from dynamic self-assembly. Our study proposes a two-step mechanism to form a supramolecular hydrogel system: (1) the formation of micelles, and (2) micelle association with α-cyclodextrin (α-CD) due to threading of PEGMA in the α-CD cavity, forming inclusion complexes. Using this mechanism, a supramolecular hydrogel made from a tri-component copolymer PLLA/DMAEMA/PEGMA and α-CD was fabricated for the first time and characterized in terms of its structural, morphological, and rheological properties.

A shape memory copolymer based on 2-(dimethylamino)ethyl methacrylate and methyl allyl polyethenoxy ether for potential biological applications

This study reports a novel shape memory copolymer synthesized with 2-(dimethylamino)-ethyl-methacrylate (DMAEMA) and methyl-allyl-polyethenoxy-ether (TPEG) for potential biological applications.

Synthesis, rapid responsive thickening, and self-assembly of brush copolymer poly(ethylene oxide)-graft-poly(N,N-dimethylaminoethyl methacrylate) in aqueous solutions

Double hydrophilic brush copolymer poly(ethylene oxide)-graft-poly(N,N-dimethylaminoethyl methacrylate) (PEO-g-PDMAEMA) was successfully prepared via atom transfer radical polymerization (ATRP). We investigated the pH/thermoresponsive behaviors of PEO-g-PDMAEMA brush-shaped copolymer concentrated aqueous solutions by rheology. The observed LCST strongly decreased with increasing pH of the solutions, which was lower than that of linear block copolymer for different pH, indicating rapid thermoresponsiveness of the brush PDMAEMA chains. An unexpected shear thickening behavior was observed and could be tuned by the pH, resulting from the mobile nature and tractive force of the densely grafted hydrophobic chains of PDMAEMA at high pH. Self-assembly of the brush copolymer in a different pH and ionic strength environment was studied by transmission electron microscopy. A wormlike cylinder structure was formed at low pH. Fractals were observed for the brush copolymer aqueous solution in the presence of NaCl. The results showed that by adjusting the pH and NaCl concentration of the dispersions fractal aggregates with different topology were obtained. The observations reported here can supply a better understanding of the molecular self-assembling nature and be used to develop responsive materials with better performance.

Hierarchical self-assembly of polyhedral oligomeric silsesquioxane end-capped stimuli-responsive polymer: from single micelle to complex micelle

Responsive polymeric micelles have been widely studied because of their potential use in nanocontainers and nanocarriers. In this study, polyhedral oligomeric silsesquioxane (POSS) end-capped poly[2-(dimethylamino)ethyl methacrylate] (POSS-PDMAEMA), a stimuli-responsive organic-inorganic hybrid polymer, was synthesized via atom transfer radical polymerization (ATRP) using POSS-Br as a macroinitiator. The self-assembly behaviors of POSS-PDMAEMA in aqueous solution were studied by fluorescence probe, transmission electron microscopy (TEM), dynamic light scattering (DLS), high-resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD). The results revealed two self-assembly processes of POSS-PDMAEMA. First they self-assembled into a single micelle with the POSS molecules forming a crystal core and the PDMAEMA chains stretching as a corona. Then the single micelles, as building blocks, were able to reversibly form a hierarchical micelle-on-micelle structure (complex micelle) under external stimuli.

Functional Polyether-based Amphiphilic Block Copolymers Synthesized by Atom-transfer Radical Polymerization

This review deals with the synthesis, physical properties, and applications of amphiphilic block copolymers based on hydrophilic poly(ethylene oxide) (PEO) or hydrophobic poly(propylene oxide) (PPO). Oligomeric PEO and PPO are frequently functionalized by converting their OH end groups into macroinitiators for atom-transfer radical polymerization. They are then used to generate additional blocks as part of complex copolymer architectures. Adding hydrophobic and hydrophilic blocks, respectively, leads to polymers with amphiphilic character in water. They are surface active and form micelles above a critical micellization concentration. Together with recent developments in post-polymerization techniques through quantitative coupling reactions (‘click’ chemistry) a broad variety of tailored functionalities can be introduced to the amphiphilic block copolymers. Examples are outlined including stimuli responsiveness, membrane penetrating ability, formation of multi-compartmentalized micelles, etc.