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Richard Hoogenboom - One of the best experts on this subject based on the ideXlab platform.
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unexpected reactivity switch in the statistical copolymerization of 2 Oxazolines and 2 oxazines enabling the one step synthesis of amphiphilic gradient copolymers
Journal of the American Chemical Society, 2019Co-Authors: Ondrej Sedlacek, Bart Verbraeken, Kathleen Lava, Sabah Kasmi, Bruno G De Geest, Richard HoogenboomAbstract:Poly(2-oxazoline)s and, more recently, also poly(2-oxazine)s represent an emerging class of polymers with a broad range of applications. Surprisingly, to date, the statistical copolymerization of these two cyclic imino ether monomers has not yet been reported. Herein, we demonstrate that the statistical copolymerization of 2-oxazines with 2-Oxazolines can lead to the formation of amphiphilic gradient copolymers in a single step. These gradient copolymers combine the high structural modularity of poly(2-oxazoline)s with the excellent biological properties of poly(2-oxazine)s, especially poly(2-methyl-2-oxazine). The copolymerization was found to proceed in a nonexpected way with the relative incorporation rates of the monomers being opposite to the reactivity observed for the corresponding homopolymerizations. In fact, the statistical copolymerizations lead to faster incorporation of the 2-oxazine followed by a gradual transition toward the 2-oxazoline. The self-assembly properties of the prepared amphiphilic poly[(2-methyl-2-oxazine)- grad-(2-butyl-2-oxazoline)] (PMeOzi- grad-PBuOx) as well as the thermoresponsive poly[(2-methyl-2-oxazine)- grad-(2-propyl-2-oxazoline)] (PMeOzi- grad-PPrOx) confirmed their potential as stimuli-responsive nonionic surfactants for various applications. Finally, the noncytotoxic character and cellular uptake of PMeOzi- grad-PBuOx copolymers was confirmed in vitro in SKOV3 cells.
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the chemistry of poly 2 oxazoline s
European Polymer Journal, 2017Co-Authors: Bart Verbraeken, Bryn D Monnery, Kathleen Lava, Richard HoogenboomAbstract:Abstract As we celebrate the 50th birthday of the discovery of poly(2-alkyl/aryl-2-oxazoline)s (PAOx) this year we see a research field that is rapidly expanding after some lesser academic activity in the nineties. This renewed interest in PAOx stems from the fact that this polymer class combines high synthetic versatility with good biocompatibility, opening up the way to highly functional (biocompatible) materials. PAOx are prepared by living cationic ring-opening polymerization (CROP) of 2-Oxazolines, which will be the in-depth focus off this review. The variety of 2-oxazoline monomers that are readily available or can easily be synthesized, allows for tuning of polymer properties and introduction of diverse functionalities as well as provides access to different polymer architectures. Moreover, thanks to the living nature of the CROP, well-defined polymers with narrow molar mass distribution and high end-group fidelity can be obtained.
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Fluorinated 2‑Alkyl-2-Oxazolines of High Reactivity: Spacer-Length-Induced Acceleration for Cationic Ring-Opening Polymerization As a Basis for Triphilic Block Copolymer Synthesis
2017Co-Authors: Leonid I. Kaberov, Richard Hoogenboom, Bart Verbraeken, Anna Riabtseva, Jiri Brus, Yeshayahu Talmon, Petr Stepanek, Sergey K. FilippovAbstract:The synthesis of defined triphilic terpolymers with hydrophilic, lyophilic, and fluorophilic blocks is an important challenge as a basis for the development of multicompartment self-assembled structures with potential for, e.g., cascade catalysis and multidrug loading. The synthesis of fluorophilic poly(2-oxazoline)s generally suffers from a very low reactivity of fluorinated 2-oxazoline monomers in cationic ring-opening polymerization (CROP). We report a systematic study on overcoming the extremely low reactivity of 2-perfluoroalkyl-2-Oxazolines in CROP by the insertion of methyl and ethyl hydrocarbon spacers between the 2-oxazoline ring and the trifluoromethyl group. The kinetic studies showed the gradual increase of the rate of polymerization with increasing of the hydrocarbon spacer length. The monomer with an ethyl spacer was found to have similar reactivity as 2-alkyl-2-Oxazolines and allowed the synthesis of defined triphilic triblock copolymers
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poly 2 ethyl 2 oxazoline block polycarbonate block copolymers from improved end group control in poly 2 oxazoline s to chain extension with aliphatic polycarbonate through a fully metal free ring opening polymerisation process
Polymer Chemistry, 2016Co-Authors: Victor Retamero De La Rosa, Richard Hoogenboom, Sarah Tempelaar, Philippe Dubois, Laetitia MespouilleAbstract:Block copolymer micelles hold great promise for developing next generation drug delivery vehicles to improve therapeutics. In this work, the biocompatibility of poly(2-alkyl-2-oxazoline)s (PAOx) was combined with the biodegradability and biocompatibility of aliphatic polycarbonates through the preparation of block copolymers. These well-defined blocks were prepared via cationic ring-opening polymerisation (CROP) of 2-Oxazolines followed by the organocatalytic ring-opening polymerisation (ROP) of cyclic carbonate monomers. The improved synthesis of hydroxyl terminated poly(2-ethyl-2-oxazoline)s (PEtOx-OH) is reported allowing high end-group fidelity. These polymers were used as macroinitiators in the controlled ROP of various cyclic carbonate monomers (TMC and benzyl, allyl, propargyl, bromide and morpholino functional monomers) resulting in well-defined amphiphilic block copolymers.
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Microwave-assisted cationic ring-opening polymerization of 2-Oxazolines.
Advances in polymer science = Fortschritte der Hochpolymeren-Forschung, 2015Co-Authors: Klaus Peter Luef, Richard Hoogenboom, Ulrich S. Schubert, Frank WiesbrockAbstract:More than any other polymer class, the synthesis of (co-)poly(2-oxazoline)s has benefited tremendously from the introduction of microwave reactors into chemical laboratories. This review focuses on research activities in the area of (co-)poly(2-oxazoline)s prepared by microwave-assisted syntheses and summarizes the current state-of-the-art for microwave-assisted syntheses of 2-oxazoline monomers, microwave-assisted ring-opening (co-)polymerizations of 2-Oxazolines, and prominent examples of post-polymerization modifications of (co-)poly(2-oxazoline)s. Special attention is paid to kinetic analyses of the microwave-assisted polymerization of 2-Oxazolines and to the discussion of non-thermal microwave effects.
Bart Verbraeken - One of the best experts on this subject based on the ideXlab platform.
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unexpected reactivity switch in the statistical copolymerization of 2 Oxazolines and 2 oxazines enabling the one step synthesis of amphiphilic gradient copolymers
Journal of the American Chemical Society, 2019Co-Authors: Ondrej Sedlacek, Bart Verbraeken, Kathleen Lava, Sabah Kasmi, Bruno G De Geest, Richard HoogenboomAbstract:Poly(2-oxazoline)s and, more recently, also poly(2-oxazine)s represent an emerging class of polymers with a broad range of applications. Surprisingly, to date, the statistical copolymerization of these two cyclic imino ether monomers has not yet been reported. Herein, we demonstrate that the statistical copolymerization of 2-oxazines with 2-Oxazolines can lead to the formation of amphiphilic gradient copolymers in a single step. These gradient copolymers combine the high structural modularity of poly(2-oxazoline)s with the excellent biological properties of poly(2-oxazine)s, especially poly(2-methyl-2-oxazine). The copolymerization was found to proceed in a nonexpected way with the relative incorporation rates of the monomers being opposite to the reactivity observed for the corresponding homopolymerizations. In fact, the statistical copolymerizations lead to faster incorporation of the 2-oxazine followed by a gradual transition toward the 2-oxazoline. The self-assembly properties of the prepared amphiphilic poly[(2-methyl-2-oxazine)- grad-(2-butyl-2-oxazoline)] (PMeOzi- grad-PBuOx) as well as the thermoresponsive poly[(2-methyl-2-oxazine)- grad-(2-propyl-2-oxazoline)] (PMeOzi- grad-PPrOx) confirmed their potential as stimuli-responsive nonionic surfactants for various applications. Finally, the noncytotoxic character and cellular uptake of PMeOzi- grad-PBuOx copolymers was confirmed in vitro in SKOV3 cells.
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the chemistry of poly 2 oxazoline s
European Polymer Journal, 2017Co-Authors: Bart Verbraeken, Bryn D Monnery, Kathleen Lava, Richard HoogenboomAbstract:Abstract As we celebrate the 50th birthday of the discovery of poly(2-alkyl/aryl-2-oxazoline)s (PAOx) this year we see a research field that is rapidly expanding after some lesser academic activity in the nineties. This renewed interest in PAOx stems from the fact that this polymer class combines high synthetic versatility with good biocompatibility, opening up the way to highly functional (biocompatible) materials. PAOx are prepared by living cationic ring-opening polymerization (CROP) of 2-Oxazolines, which will be the in-depth focus off this review. The variety of 2-oxazoline monomers that are readily available or can easily be synthesized, allows for tuning of polymer properties and introduction of diverse functionalities as well as provides access to different polymer architectures. Moreover, thanks to the living nature of the CROP, well-defined polymers with narrow molar mass distribution and high end-group fidelity can be obtained.
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Fluorinated 2‑Alkyl-2-Oxazolines of High Reactivity: Spacer-Length-Induced Acceleration for Cationic Ring-Opening Polymerization As a Basis for Triphilic Block Copolymer Synthesis
2017Co-Authors: Leonid I. Kaberov, Richard Hoogenboom, Bart Verbraeken, Anna Riabtseva, Jiri Brus, Yeshayahu Talmon, Petr Stepanek, Sergey K. FilippovAbstract:The synthesis of defined triphilic terpolymers with hydrophilic, lyophilic, and fluorophilic blocks is an important challenge as a basis for the development of multicompartment self-assembled structures with potential for, e.g., cascade catalysis and multidrug loading. The synthesis of fluorophilic poly(2-oxazoline)s generally suffers from a very low reactivity of fluorinated 2-oxazoline monomers in cationic ring-opening polymerization (CROP). We report a systematic study on overcoming the extremely low reactivity of 2-perfluoroalkyl-2-Oxazolines in CROP by the insertion of methyl and ethyl hydrocarbon spacers between the 2-oxazoline ring and the trifluoromethyl group. The kinetic studies showed the gradual increase of the rate of polymerization with increasing of the hydrocarbon spacer length. The monomer with an ethyl spacer was found to have similar reactivity as 2-alkyl-2-Oxazolines and allowed the synthesis of defined triphilic triblock copolymers
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Block and Gradient Copoly(2-oxazoline) Micelles: Strikingly Different on the Inside
2017Co-Authors: Sergey K. Filippov, Bart Verbraeken, Petr V. Konarev, Dmitri I. Svergun, Borislav Angelov, Natalya S. Vishnevetskaya, Christine M. Papadakis, Sarah Rogers, Aurel Radulescu, Tim CourtinAbstract:Herein, we provide a direct proof for differences in the micellar structure of amphiphilic diblock and gradient copolymers, thereby unambiguously demonstrating the influence of monomer distribution along the polymer chains on the micellization behavior. The internal structure of amphiphilic block and gradient co poly(2-Oxazolines) based on the hydrophilic poly(2-methyl-2-oxazoline) (PMeOx) and the hydrophobic poly(2-phenyl-2-oxazoline) (PPhOx) was studied in water and water–ethanol mixtures by small-angle X-ray scattering (SAXS), small-angle neutron scattering (SANS), static and dynamic light scattering (SLS/DLS), and 1H NMR spectroscopy. Contrast matching SANS experiments revealed that block copolymers form micelles with a uniform density profile of the core. In contrast to popular assumption, the outer part of the core of the gradient copolymer micelles has a distinctly higher density than the middle of the core. We attribute the latter finding to back-folding of chains resulting from hydrophilic–hydrophobic interactions, leading to a new type of micelles that we refer to as micelles with a “bitterball-core” structure
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Model-Based Visualization and Understanding of Monomer Sequence Formation in Gradient Copoly(2-oxazoline)s On the basis of 2-Methyl-2-oxazoline and 2-Phenyl-2-oxazoline
Macromolecules, 2015Co-Authors: Paul H. M. Van Steenberge, Richard Hoogenboom, Bart Verbraeken, Marie-françoise Reyniers, Dagmar R. D'hoogeAbstract:For the first time, the formation of monomer sequences of individual macromolecules during cationic ring-opening copolymerization (CROcoP) of 2-methyl-2-oxazoline (MeOx) and 2-phenyl-2-oxazoline (PhOx) in acetonitrile (3 mol L–1; 100–140 °C; target degree of polymerization (DP): 50–400) is visualized via kinetic Monte Carlo simulations with model parameters optimized based on experimental data. It is shown that chain transfer via β-elimination and branching reactions are required to describe the experimental data. At complete monomer conversion for target DPs below 200, at most 5% of the chains are macromonomers and the average number of branches per chain remains below 15%. A higher amount of chains with a defined, steeper MeOx to PhOx gradient is obtained by lowering the polymerization temperature albeit at the expense of polymerization time. The simulations results highlight the great potential of CROcoP of 2-Oxazolines for the direct synthesis of well-defined steep gradient copolymers.
Frank Wiesbrock - One of the best experts on this subject based on the ideXlab platform.
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UV-mediated thiol-ene click reactions for the synthesis of drug-loadable and degradable gels based on copoly(2-oxazoline)s
European Polymer Journal, 2017Co-Authors: Klaus Peter Luef, Charlotte Petit, Bettina Ottersböck, Gernot Oreski, Francis Ehrenfeld, Bruno Grassl, Stéphanie Reynaud, Frank WiesbrockAbstract:An 80-membered library of gels composed of monofunctional 2-ethyl-2-oxazoline and 2-nonyl-2-oxazoline and one of four selected difunctional 2-Oxazolines (containing either ether or ester bonds) were synthesized by microwave-assisted ring-opening polymerizations. The difunctional 2-Oxazolines were prepared from the thiol-ene reaction of glycol dimercaptoacetate or 2,2′-(ethylenedioxy)diethanethiol and 2-but-3′-enyl-2-oxazoline or 2-dec-9′-enyl-2-oxazoline. 53 of the gels exhibited glass-transition temperatures, which ranged from −5.9 to 45.3 °C. 13 Derivatives exhibited glass-transition temperatures in the range from 20 to 30 °C, which renders them stiff at room temperature and flexible at body temperature. The gels that did not contain any 2-ethyl-2-oxazoline acted as lipogels, whereas the gels that did not contain any 2-nonyl-2-oxazoline acted as hydrogels; all other gels may be classified as amphigels. The swelling degrees were measured by gravimetry and maximum swelling degrees of 6 (in water) were observed for the gels with the lowest degrees of crosslinking. In a second approach, the synthesis of crosslinked networks had been achieved by performing the polymeranalogous thiol-ene reaction of copoly(2-oxazoline)s containing olefinic side-chains and glycol dimercaptoacetate. This soft strategy enabled the straightforward loading of such gels with active pharmaceutical ingredients without altering them. This method delivered gels with selected composition exhibiting a targeted disc-shape and loaded with active pharmaceutical ingredients from one-step syntheses. The maximum swelling degrees of these specimens were found to be in accordance with the ones from the first route investigated. Preliminary degradation studies were performed at 25 °C; these types of gels were found to be degraded in alkaline media as well as by esterases.
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Microwave-assisted cationic ring-opening polymerization of 2-Oxazolines.
Advances in polymer science = Fortschritte der Hochpolymeren-Forschung, 2015Co-Authors: Klaus Peter Luef, Richard Hoogenboom, Ulrich S. Schubert, Frank WiesbrockAbstract:More than any other polymer class, the synthesis of (co-)poly(2-oxazoline)s has benefited tremendously from the introduction of microwave reactors into chemical laboratories. This review focuses on research activities in the area of (co-)poly(2-oxazoline)s prepared by microwave-assisted syntheses and summarizes the current state-of-the-art for microwave-assisted syntheses of 2-oxazoline monomers, microwave-assisted ring-opening (co-)polymerizations of 2-Oxazolines, and prominent examples of post-polymerization modifications of (co-)poly(2-oxazoline)s. Special attention is paid to kinetic analyses of the microwave-assisted polymerization of 2-Oxazolines and to the discussion of non-thermal microwave effects.
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Microwave Accelerated Polymerization of 2‐Phenyl‐2‐oxazoline: Microwave or Temperature Effects?
Macromolecular Rapid Communications, 2005Co-Authors: Richard Hoogenboom, Mam Mark Leenen, Frank Wiesbrock, Ulrich S. SchubertAbstract:Summary: Investigations regarding the cationic ring-opening polymerization of 2-phenyl-2-oxazoline under microwave irradiation and conventional heating are reported. This study was inspired by contradictory reports of the (non-)existence of non-thermal microwave effects that might accelerate the cationic ring-opening of 2-Oxazolines. The polymerization of 2-phenyl-2-oxazoline was investigated under pressure in acetonitrile and under reflux (or at the boiling point of butyronitrile in a closed vessel) in butyronitrile utilizing a single-mode microwave reactor and automated synthesis robots with conventional heating.
Laixi Wang - One of the best experts on this subject based on the ideXlab platform.
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efficient glycosynthase mutant derived from mucor hiemalis endo β n acetylglucosaminidase capable of transferring oligosaccharide from both sugar oxazoline and natural n glycan
Journal of Biological Chemistry, 2010Co-Authors: Midori Umekawa, Takayuki Higashiyama, Wei Huang, Hisashi Ashida, Kenji Yamamoto, Laixi WangAbstract:Abstract Endo-M, an endo-β-N-acetylglucosaminidase from Mucor hiemalis, is a family 85 glycoside hydrolase. This enzyme is unique in that it can transfer en bloc the oligosaccharide of various types of N-glycans onto different acceptors, and thereby it enzymatically generates diverse glycoconjugates. In this study, we performed mutational and kinetic studies focusing on a key catalytic asparagine 175 of Endo-M. We have shown that most of the Asn-175 mutants had significantly diminished hydrolysis activity but acted as glycosynthases capable of using synthetic sugar oxazoline for transglycosylation. Our results confirm the critical role of this asparagine residue in promoting the formation of an oxazolinium ion intermediate in the first step of the substrate-assisted catalysis. Interestingly, the N175Q mutant was found to possess dramatically enhanced glycosynthase-like activity with sugar oxazoline in comparison with N175A and a transglycosidase-like activity with “natural” N-glycan as well. These results also implicated the significance of amide side chain in the asparagine 175 of Endo-M for promoting oxazoline transglycosylation in the second step of the catalysis. The highly efficient syntheses of glycopeptides/glycoproteins by N175Q combined with synthetic sugar Oxazolines or natural N-glycan substrates were exemplified. In addition, we also identified several previously unknown residues that seem to play a role in the catalysis of Endo-M.
Rainer Jordan - One of the best experts on this subject based on the ideXlab platform.
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Microstructured poly(2-oxazoline) bottle-brush brushes on nanocrystalline diamond
Physical chemistry chemical physics : PCCP, 2010Co-Authors: Naima A. Hutter, Andreas Reitinger, Ning Zhang, Marin Steenackers, Oliver Aneurin Williams, Jose A. Garrido, Rainer JordanAbstract:We report on the preparation of microstructured poly(2-oxazoline) bottle-brush brushes (BBBs) on nanocrystalline diamond (NCD). Structuring of NCD was performed by photolithography and plasma treatment to result in a patterned NCD surface with oxidized and hydrogenated areas. Self-initiated photografting and photopolymerization (SIPGP) of 2-isopropenyl-2-oxazoline (IPOx) resulted in selective grafting of poly(2-isopropenyl-2-oxazoline) (PIPOx) polymer brushes only at the oxidized NCD areas. Structured PIPOx brushes were converted by methyl triflate into the polyelectrolyte brush macroinitiator for the living cationic ring-opening polymerization (LCROP) of 2-Oxazolines. The LCROP was performed with 2-ethyl-2-oxazoline (EtOx) as well as 2-(carbazolyl)ethyl-2-oxazoline (CarbOx) as monomers, resulting in structured bottle-brush brushes (BBB) with different pendant side chains and functionalities. FT-IR spectroscopy, fluorescence microscopy, and AFM measurements indicated a high side chain grafting density as well as quantitative and selective reactions. Poly(2-oxazoline) BBBs containing hole conducting carbazole moieties on NCD as electrode material may open the way to advanced amperometric biosensing systems.
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Cylindrical Molecular Brushes of Poly(2-oxazoline)s from 2-Isopropenyl-2-oxazoline
Macromolecules, 2009Co-Authors: Ning Zhang, Stephan Huber, Anita Schulz, Robert Luxenhofer, Rainer JordanAbstract:We report on the synthesis and characterization of cylindrical molecular brushes based on poly(2-oxazoline)s (POx). The dual-functional monomer, 2-isopropenyl-2-oxazoline (IPOx), was first converted to a poly(2-isopropenyl-2-oxazoline), backbone by free radical (PIPOxR) or living anionic polymerization (PIPOxA). Quantitative reaction with methyl triflate yields a macroinitiator salt (PIPOxOTfR/A) for the preparation of molecular brushes via the grafting from approach by living cationic polymerization of 2-Oxazolines (2-methyl-, 2-ethyl-, and 2-isopropyl-2-oxazoline). Characterization of the resulting molecular brushes by NMR and FTIR spectroscopy indicates a very high side chain grafting density and quantitative reactions. Visualization of adsorbed molecular brushes by AFM corroborates this assumption. Furthermore, the lower critical solution temperatures of the POx molecular brushes were determined. The transition temperatures were found to be very defined, reversible, and with no noticeable hysteresis.
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Kinetic Investigations on the Polymerization of 2-Oxazolines Using Pluritriflate Initators
Macromolecular Rapid Communications, 2008Co-Authors: Robert Luxenhofer, Manuela C. I. Bezen, Rainer JordanAbstract:In our ongoing efforts to develop poly(2-oxazoline)s (POx) for biomedical applications, we report on the preparation of defined, star-like hydrophilic POx. Using pluritriflate initiators, we show, through online kinetic measurements by gas chromatography, that multiple initiating groups are of equal reactivity for the initiation of the polymerization of 2-Oxazolines. The overall polymerization rate increases linearly with the number of initiator functions per molecule. Thus, all initiating moieties are of the same reactivity and all arms grow at the same rate. This is crucial for the establishment of a meaningful structure-property relationship for polymers of star architectures.
