Cyclodextrins in Polymer Synthesis: Supramolecular Cyclodextrin Complexes of Pyrrole and 3,4-Ethylenedioxythiophene and Their Oxidative Polymerization

Abstract

Dedicated to Professor Helmut Ringsdorf on the occasion of his 70th birthday p-Conjugated polymers, often referred to as conducting polymers or synthetic metals, have created enormous interest over the past 25 years. Due to the substantial p-electron delocalization along their backbones, these polymers show interesting (nonlinear) optical properties and become good electronic conductors when oxidized or reduced. Hence, a prominent and active role is foreseen for these compounds in a variety of practical applications such as information storage, optical signal processing, electromagnetic interference (EMI) shielding, and solar energy conversion, as well as rechargeable batteries, light emitting diodes, field effect transistors, printed circuit boards, sensors, and antistatic materials. [1] Conducting polymers can be prepared by various chemical and electrochemical polymerization techniques. Due to the physical characteristics of the monomers used, electrochemical polymerization of these compounds meets with several disadvantages that hamper their commercialization. For example, low solubility of monomers in water forces the use of less environmentally friendly organic solvents such as chloroform or acetonitrile, whereas their relatively high vapor pressure causes unpleasant and unhealthy odors. A further disadvantage is the tendency of the monomers to degrade due to exposure to air and/or light. In order to overcome these problems we investigated the use of cyclodextrins (CDs) as inert host molecules.Cyclodextrins are cyclic oligosaccharides built up from 1,4-glucopyranose units that exhibit a torus-shaped structure with a hydrophobic cavity and a hydrophilic exterior. They are increasingly utilized for their inclusion complexing properties, [2] resulting in a large number of applications in the pharmaceutical, food, and cosmetic industry. Furthermore, there are numerous studies showing that CDs can be used in organic chemistry, e.g., as microvessels for organic synthesis [3] and in polymer chemistry. Examples of the latter include the use of CD as an initiator for polymerizations, [4] the radical polymerization of CD complexed methacrylate esters or other monomers, [5] and CD polymers that are used as stationary phases for chromatography. [6] According to the literature, there are only few publications known that involve the complexation of CDs with (hetero)-aromatic compounds, that can be polymerized to p-conjugated polymers. De Feyter and coworkers studied the aterthiophene/g-CD complex with excited dimer fluorescence in aqueous solution, [7] whereas Dong and coworkers electrochemically polymerized an aniline/a-CD complex to exclude a certain theory regarding by-products formed during the electrochemical formation of polyaniline. [8] Lacaze and coworkers studied the electrochemical polymerization of a 2,2¢-bithiophene/hydroxypropyl-b-CD complex in water, claiming the formation of an organic solvent soluble polythiophene. [9] Recently, the same group also published the electrochemical polymerization of s...

Novel main‐chain polyrotaxanes synthesized via ATRP of HPMA in aqueous media

“…weaken this competitive inclusion complexation effect, Meb-CD has come into our sight since it has a higher solubility than b-CD and has been widely used to include a variety of vinyl monomers to enhance their solubility in aqueous media. 31,32 Here Meb-CD was used to include HPMA to depress the dethreading tendency of b-CD off the Pluronic F127 backbone. This strategy was shown to be effective to keep more b-CDs on the polymeric chain while the PRs yields were also improved moderately.…”

Cyclodextrin in polymer chemistry: Kinetic studies on the free-radical polymerization of cyclodextrin-complexed styrene from homogeneous aqueous solution

“…Furthermore, the preparation and polymerization of equimolar cyclodextrin complexes of commercial standard monomers like styrene 1 and methyl methacrylate (MMA have been described. It was also shown that the precipitation polymerization of a cyclodextrin complex of a poorly water-soluble monomer like MMA can be described by kinetic equations similar to those for the classical polymerization in solution [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20].…”

A 3D Electroactive Polypyrrole-Collagen Fibrous Scaffold for Tissue Engineering

“…The ability of -cyclodextrin to encapsulate lipophilic compounds, such as pyrrole, in its hydrophobic activity to form a water-soluble inclusion complex (IC) is well documented [34]. IC formation can significantly lower the vapor pressure of pyrrole.…”

“…Hence, pyrrole/-cyclodextrin ICs represents a strategy by which pyrrole may be effectively encapsulated within IPC fibers for subsequent polymerization. Additionally, chemical polymerization by FeCl 3 of cyclodextrin encapsulated pyrrole has been reported to precipitate polypyrrole as a powder, with cyclodextrin -hosts‖ retained in solution from which they may be efficiently separated from polypyrrole by sedimentation and washing with water [34].…”