December 2015 – Polymer Chemistry Blog

Archive for December, 2015

Paper of the month: Solvent-free mechanochemical synthesis of a bicyclononyne tosylate: a fast route towards bioorthogonal clickable poly(2-oxazoline)s

23 Dec 2015

Glassner et. al. report a new solvent-free mechanochemical synthesis of a bicyclononyne tosylate.

The strain promoted azide-alkyne cycloaddition of cyclooctynes (SPAAC) is a popular bioorthogonal reaction that enables the tracking of biomacromolecules in living systems. Among the various cylooctynes that have been developed for SPAAC reactions, derivatives of bicyclo[6.1.0]non-4-yne (BCN) have attracted considerable interest for a number of reasons including their low hydrophobicity and ability to undergo fast cycloadditions not only with azides but also with nitrones. At the same time, poly(2-oxazoline)s (PAOx) represent a promising class of polymers for biomedical applications that can easily incorporate clickable end-groups by employing functional initiators or terminators. In this paper, Hoogenboom and co-workers present the first mechanochemical synthesis of a BCN tosylate (BCN-OTs) initiator via solvent-free reaction conditions utilizing high speed vibration milling instead of manual grinding. The BCN-OTs was subsequently used for the cationic ring opening polymerization (CROP) of 2-ethyl-2-oxazoline (EtOx) yielding a well-defined polymer and demonstrating controlled/living polymerization features such as narrow molecular weight distributions and high chain end fidelity. This represents a rapid route to prepare defined BCN functionalized PEtOx that can be used for bioorthogonal strain-promoted conjugation reactions. This was successfully demonstrated for the synthesis of a PS-b-PEtOx copolymer and a PEtOx-protein conjugate. As such, BCN-OTs may find potential applications as intermediate in the synthesis of functional BCN derivatives and BCN-PAOx. In addition, the ball-milling methodology utilized for this study is a promising tool for the synthesis of other unstable/highly reactive tosylates.

Tips/comments directly from the authors:

1) KOH and K₂CO₃ should be finely grounded and dried in a vacuum oven prior to use.

2) During the synthesis of BCN-OTs, removal of solvents has to be performed at ambient temperature (turn of the heating bath of the rotary evaporator).

3) BCN-OTs has to be used immediately for the next step because of its limited stability at ambient conditions.

Solvent-free mechanochemical synthesis of a bicyclononyne tosylate: a fast route towards bioorthogonal clickable poly(2-oxazoline)s by M. Glassner, S. Maji, V. de la Rosa, N. Vanparijs, K. Ryskulova, B. De Geest and R. Hoogenboom, Polym. Chem., 2015, 6, 8354-8359

Dr. Athina Anastasaki is a Web Writer for Polymer Chemistry. She is currently a Warwick (UK)/ Monash (Australia) research fellow working under the Monash Alliance. Visit http://haddleton.org/group-members for more information.

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Editorial Board’s Top Picks: Emily Pentzer

04 Dec 2015

Emily Pentzer is an Associate Editor for Polymer Chemistry and an Assistant Professor of Chemistry at Case Western Reserve University, USA. Her research addresses application-based materials problems in the areas of energy harvesting, management, and storage. She uses synthetic chemistry to tailor molecular design and control self-assembly for the preparation and study of novel conductive materials with controlled domain sizes and interfaces.

You can find all Editorial Board’s Top Picks papers in our web collection.

Focus on PAH building blocks for electronically active and porous polymers (Associate Editor: Prof Emily Pentzer Case Western Reserve University, USA)

Polyaromatic hydrocarbons (PAHs) are attractive building blocks for electronically active and porous organic polymers. For these applications, the preparation and isolation of appropriate polymeric structures is needed to provide the desired properties. PAHs are typically incorporated into conjugated polymers by transition metal-catalyzed cross-coupling reactions, and their solubility and solution processability is ensured by substitution with alkyl groups; recent interest has focused on accessing reduced band gap structures. Alternatively, for the preparation of porous organic polymers, the tendency of PAHs to aggregate through p-p interactions must be overcome, and alkyl groups are disadvantageous for gas adsorption/storage. Recent advances in the design and synthesis of PAH-containing polymers have helped expand the usefulness of these heteroatom-free systems.

1. Anthanthrene as a large PAH building block for the synthesis of conjugated polymers
Antoine Lafleur-Lambert,Jean-Benoît Giguère and Jean-Francois Morin
Polym. Chem., 2015, 6, 4859-4863

Aromatic anthanthrene is readily available from the common dye vat orange 3 and can be used to prepare PAH-containing polymers. Morin and coworkers report the preparation of a series of anthanthrene-based conjugated polymers. The anthanthrene unit has branched alkyl substituents to control solubility and was copolymerized with electron rich and electron poor aryl comonomers. The absorption spectra of these polymers range from 450 to 850 nm, depending on the constituent materials. The series of novel polymers all showed similar LUMO levels, and variation of the HOMO levels show no trends based on the comonomer identity. These results indicate that both the HOMO and the LUMO orbitals are located on the anthanthrene units, and are not heavily influenced by the comonomer identity.

2. Dicyclopenta[cd,jk]pyrene based acceptors in conjugated polymers
Sambasiva R. Bheemireddy and Kyle N. Plunkett
Polym. Chem., 2016, Advance Article

In this study, Plunkett and Bheemireddy report the use of the PAH dicyclopentapyrene, as an acceptor unit in conjugated polymers. This alkylated monomer was copolymerized with various electron donor comonomers including thiophene, bithiophene, and diethynyl benzene. In the thin film, these polymers show broad absorption profiles, from ~320-720 nm, corresponding to band gaps of ~1.7 eV. The identity of the comonomer with the PAH had little influence on the HOMO and LUMO levels, inconsistent with traditional donor-acceptor theory for reduced bandgap materials. In fact, DFT calculations show the LUMO orbital distribution across the series is essentially unchanged and mostly located on the PAH unit (as expected), but surprisingly, the HOMO orbitals are also localized to the PAH unit for the thiophene and bithiophene polymers.

3. Di(naphthalen-2-yl)-1,2-diphenylethene-based conjugated polymers: aggregation-enhanced emission and explosive detection
Mengxia Gao, Yue Wu, Bin Chen, Bairong He, Han Nie, Tingyan Li, Fupeng Wu, Wenjun Zhou, Jian Zhou and Zujin Zhao
Polym. Chem., 2015, 6, 7641-7645

Di(naphthalene-2-yl)-1,2-diphenylethene is used as a building block by Zhao and coworkers to prepare fluorescent conjugated polymers which show aggregation induced emission. Addition of the poor solvent water to these polymers in THF causes them to aggregate and essentially turns on the fluorescence of the materials by preventing non-radiative excited state decay. DFT calculations show the HOMO and LUMO orbitals are significantly distributed over both comonomers, as well as the pendant naphthyl groups, indicating good intramolecular orbital overlap. These materials further show potential to detect explosives under aqueous conditions, as the fluorescence is quenched in the presence of picric acid.

4. Facile approach for preparing porous organic polymers through Bergman cyclization
Xian-Mei Zhang, Xuesong Ding, Aiguo Hu and Bao-Hang Han
Polym. Chem., 2015, 6, 4734-4741

The Bergman cyclization reaction was used to prepare microporous polymers from a triphenylene-based monomer that contains three ene-diyne moieties. This catalyst-free and thermally induced intramolecular cyclization produces three 1,4-benzene biradical per monomer that undergo intermolecular coupling to yield the porous polymer. Although the monomers themselves are planar, they link together in a non-planar fashion to give a porous, high surface area material. Han and coworkers then demonstrate that the novel micorporous polymers show high adsorption capacity for both hydrogen and carbon dioxide.

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Author of the Month: Prof. Dr. Ir. Bruno De Geest

04 Dec 2015

Prof. Dr. Ir. Bruno De Geest graduated as Chemical Engineer in 2003 from Ghent University where he obtained his PhD in pharmaceutical sciences in 2006 on polyelectrolyte multilayer capsules for biomedical applications. For his PhD work he was awarded the graduate student award for pharmaceutical technology from the AAPS and the Andreas Deleenheer award from Ghent University. After 2 years of postdoctoral research at Utrecht University (The Netherlands) he returned to Ghent University at the Department of Pharmaceutics. From October 2012 onwards he is appointed as professor in Biopharmaceutical Technology. Bruno De Geest has authored over 90 papers and his research group focus on the interface between materials science and life science with a particular interest in polymer chemistry, immunology and anticancer therapy.

Research website: http://brdegeest.wix.com/biopharmtech-degeest

What was your inspiration in becoming a chemist?

Chemistry offers a scientist the ability to create things using molecular scale building blocks, which appeared a very attractive concept to me. I’m a chemical engineer, thus not a hard core chemist by training. In 3^rd year at university we had organic chemistry and later on polymers taught by Filip Du Prez who was then just appointed as professor. These courses awakened a strong interest in polymer chemistry and this interest still fuels the ambition of our lab to create new materials that could hopefully be of benefit for human medicine.

What was the motivation to write your Polymer Chemistry article?

One of the main focuses of our research group in nanoparticulate vaccine delivery. While endeavoring to attach vaccine antigens to polymeric nanoparticles we noticed that the efficiency of conjugating a polymer to a protein is disappointingly low. Therefore we decided at comparing head-to-head different conjugation chemistries based on functional RAFT chain transfer agents for grafting-onto protein conjugation. The message of our paper is twofold. Firstly it gives a guide to which chemistries as more efficient than others, at least for the specific cases we have tested. Secondly, it urges the need for more efficient polymer-protein conjugation strategies.

Why did you choose Polymer Chemistry to publish your work? (DOI: 10.1039/C4PY01224K)

Polymer Chemistry has high visibility in the chemical and materials science community and publishes a high number of papers dealing with topics on controlled radical polymerization and biomedical applications. In addition, the paper will be published as part of the upcoming Emerging Investigator Issue. I’m delighted to contribute especially with this paper as it is a signature paper for our current research line.

In which upcoming conferences may our readers meet you?

I’m attending the ACS Spring Meeting in Denver in March where together with Prof. Aaron Esser-Kahn we are organizing a POLY symposium on ‘Interacting with the immune system using polymeric systems’.

How do you spend your spare times?

I’m a keen cyclist and a love to ride with my race bike trough the Flemish Ardennes. This region south of Ghent towards the Walloon border is well known for the spring cycling classics and it is a privilege to ride the same roads and climb the same cobblestone hills as the pro cyclists.

Which profession would you choose if you were not a scientist?

I think I would have studied sciences anyway, but in stead of becoming a researcher I would like be a teacher. I have always enjoyed working together with young people.

Polymer-protein conjugation via a ‘grafting to’ approach – a comparative study of the performance of protein-reactive RAFT chain transfer agents

N. Vanparijs, S. Maji, B. Louage, L. Voorhaar, D. Laplace, Q. Zhang, Y. Shi, W. E. Hennink, R. Hoogenboom and B. G. De Geest

Abstract: Efficient polymer-protein conjugation is a crucial step in the design of many therapeutic protein formulations including nanoscopic vaccine formulations, antibody-drug conjugates and to enhance the in vivo behaviour of proteins. Here we aimed at preparing well-defined polymers for conjugation to proteins by reversible addition–fragmentation chain transfer (RAFT) polymerization of both acrylates and methacrylamides with protein-reactive chain transfer agents (CTAs). These RAFT agents contain either a N-hydroxysuccinimide (NHS) or pentafluorophenyl (PFP) ester moiety that can be conjugated to lysine residues, and alternatively a maleimide (MAL) or pyridyl disulfide (PDS) moiety that can be conjugated to cysteine residues. Efficiency of the bioconjugation of these polymers to bovine and avian serum albumin was investigated as a function of stoichiometry, polymer molecular weight and the presence of reducing agents. A large molar excess of polymer was required to obtain an acceptable degree of protein conjugation. However, protein modification with N-succinimidyl-S-acetylthiopropionate (SATP) to introduce sulfhydryl groups onto primary amines, significantly increased conjugation efficiency with MAL- and PDS-containing polymers.

Cyrille Boyer is a guest web-writer for Polymer Chemistry. He is currently an associate professor and an ARC-Future Fellow in the School of Chemical Engineering, University of New South Wales (Australia) and deputy director of the Australian Centre for NanoMedicine.

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Focus on: Supramolecular Polymer Networks

02 Dec 2015

Supramolecular interactions are defined as noncovalent bonds, including: hydrogen bonding, hydrophobic association, π-π stacking, transition metal complexation and ionic interactions. Supramolecular polymer networks consist of macromolecules which are interconnected through these transient noncovalent bonds. These materials are particularly interesting as they allow the capability of adaptive, self-healing materials which have mechanical properties that are dependent on the crosslinking interactions and the polymer topology. This month three articles are highlighted which demonstrate supramolecular interactions in polymer networks to give materials with interesting properties, such as self-healing, ductility and stimuli responsive changes in mechanical properties.

Graphical abstract from article (http://xlink.rsc.org/?doi=10.1039/C5PY01214G)

1. Self-healing, malleable and creep limiting materials using both supramolecular and reversible covalent linkages, Borui Zhang, Zachary A. Digby, Jacob A. Flum, Elizabeth M. Foster, Jessica L. Sparks, Dominik Konkolewicz, Polym. Chem., 2015, 6, 7368-7372.

The combination of supramolecular and reversible crosslinks was utilized to prepare materials with self-healing properties on different time scales. Supramolecular crosslinks between 2-ureido-4[1H]-pyrimidinone moieties gave dynamic crosslinks, whilst Diels-Alder coupling between a furan and a maleimide gave a considerably less dynamic linkage. The materials showed partial healing properties at room temperature and full healing at elevated temperatures.

2. Ultraductile, notch and stab resistant supramolecular hydrogels via host–guest interactions, Mei Tan, Yulin Cui, Aidi Zhu, Han Han, Mingyu Guo, Ming Jiang, Polym. Chem., 2015, 6, 7543-7549.

The authors describe the preparation of supramolecular hydrogels which were self-healing as well as extremely ductile and notch and stab resistant. The hydrogels were based on host-guest interactions between adamantane monomers and a low molecular weight polyfunctional cyclodextrin, prepared via free radical polymerisation. Native and healed gels gave similar tensile strain–stress trends, stretching to around 50 times their original lengths with almost complete recoverability.

3. Supramolecular polymer networks based on cucurbit[8]uril host–guest interactions as aqueous photo-rheological fluids, Cindy S. Y. Tan, Jesús del Barrio, Ji Liua, Oren A. Scherman, Polym. Chem., 2015, 6, 7652-7657.

Supramolecular polymer networks are reported based upon the host-guest interactions mediated by cucurbit[8]uril with naphthyl-functionalised hydroxyethyl cellulose, methyl viologen functional styrene copolymer and a photoisomerisable azobenzene imidazolium derivative. The resulting networks exhibited light-tunable rheological properties at low mass fractions (<0.75 wt%) showing a decrease in the zero-shear viscosity and viscoelastic moduli by UV irradiation.

Dr. Fiona Hatton is a Web Writer for Polymer Chemistry. She is currently a postdoctoral researcher at KTH Royal Institute of Technology, Sweden, having completed her PhD in the Rannard group at the University of Liverpool, UK. Visit her webpage for more information.

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Polymer Chemistry Blog

Archive for December, 2015

Paper of the month: Solvent-free mechanochemical synthesis of a bicyclononyne tosylate: a fast route towards bioorthogonal clickable poly(2-oxazoline)s

Editorial Board’s Top Picks: Emily Pentzer

Author of the Month: Prof. Dr. Ir. Bruno De Geest

Polymer-protein conjugation via a ‘grafting to’ approach – a comparative study of the performance of protein-reactive RAFT chain transfer agents

Focus on: Supramolecular Polymer Networks

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