Limitations of cyclodextrin‐mediated RAFT homopolymerization and block copolymer formation

Abstract

ABSTRACT:The design and synthesis of a new hydrophobic monomer, that is, 4-(tert-butyl)phenyl 6-acrylamidohexanoate (TBP-AA-HO) and its ability to form supramolecular host/guest complexes with b-cyclodextrin (CD) is described. The aqueous CD-mediated reversible addition fragmentation chain transfer (RAFT) polymerization affords molecular masses up to 8600 g mol 21 with polydispersities between 1.2 and 1.4. The surprisingly low molecular weights for higher monomer/chain transfer agent (CTA) ratios are investigated by comparing results obtained from free radical and RAFT radical polymerization in aqueous and organic media. The results indicate a steric hindrance caused by attached CD molecules on the growing polymer chain leading to stagnation of the polymerization process due to a restricted accessibility of the reactive chain end. This hypothesis is supported by matrix-assisted laser desorption/ionization time of flight mass spectrometry. Furthermore, the CD-mediated synthesis of amphiphilic diblock copolymers in variable aqueous media is described. Hydrophilic poly(N,N-dimethylacrylamide) macroCTAs with different molecular weights are used to polymerize TBP-AA-HO at 50 C. The diblock copolymers are analyzed by 1 Hnuclear magnetic resonance spectroscopy and size exclusion chromatography. The results confirm the polymer structure and reveal similar limitations of chain growth as observed for the CDmediated homopolymerization with a limit of 7000 g mol 21 for efficient chain extension.

Preparation, characterization and molecular modeling studies of the inclusion complex of Caffeine with Beta-cyclodextrin

“…The guest molecule has been the most favorable changes in the physicochemical properties, like stability, dissolution rate, solubility, and bioavailability due to inclusion complex formation between the drug molecules with CDs [16][17][18]. The cyclodextrins are used in food [19], pharmaceuticals [20], cosmetics [21], environment protection [22], bioconversion [23][24], packing and the textile industry [25], drug delivery [26], nano-structures [27], supramolecular polymers [28], selfhealing materials [29], amphiphiles [30], bioactive materials [31] or in the solubilization of hydrophobic monomers or RAFT agents [32][33].…”

Dynamic Macromolecular Material Design—The Versatility of Cyclodextrin‐Based Host–Guest Chemistry

“…Thek ey property of CDs is their ability to form supramolecular associations with hydrophobic molecules in aqueous environments.Consequently,various CD complexes have found ab road array of applications in soft matter materials and polymer science,f or example,i ns upramolecular polymers, [16] self-healing materials, [17] hydrogels, [18] amphiphiles, [19] bioactive materials, [20] polymerization reactions, [21] drug delivery, [22] spatially controlled surface functionalization on CD monolayers (molecular printboards), [23] and responsive nanostructures. [12b] Synthetic macromolecular building blocks offer av ast range of property profiles that can be finely tuned and utilized to form well-defined complex macromolecular architec-Dynamic and adaptive materials are powerful constructs in macromolecular and polymer chemistry with awide array of applications in drug delivery,bioactive systems,and self-healing materials.V ery often, dynamic materials are based on carefully tailored cyclodextrin hostguest interactions.T he precise incorporation of these host and guest moieties into macromolecular building blocks allows the formation of complex macromolecular structures with predefined functions.Thus, dynamic materials with extraordinary adaptive property profilesresponsive to thermal, chemical, and photonic fields-become accessible.T his Review explores the hierarchical formation of dynamic materials and complex macromolecular structures from the molecular via the macromolecular to the colloidal and macroscopic level, with aspecific emphasis on the functionality and responsiveness of the assemblies,s pecifically in biological contexts.…”

Supramolecular polymer networks of building blocks prepared via RAFT polymerization

“…30,31 The host-guest interactions of CDs have been widely studied and lead to a variety of usages in polymer chemistry, e.g. for drug-delivery, 32,33 the solubilization of hydrophobic monomers, [34][35][36] the modulation of the thermoresponsive behavior of poly(N,N-diethylacrylamide) 37 and the formation of complex supramolecular architectures such as star polymers, [38][39][40][41] polymer brushes, [42][43][44] and linear block copolymers. [45][46][47] Furthermore, CDs have been employed to design polymer networks via variable approaches.…”