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Paper of the week: Block polymer miktobrushes

02 Jan 2013

Block polymers can spontaneously self-assemble into well-defined nanostructures in block selective solvents and in the bulk, offering a powerful ‘bottom up’ approach towards precisely engineered materials for many diverse applications including; microelectronics, tissue engineering, drug delivery and water purification. The increased understanding of self-assembled block polymers with varied architectures is of both fundamental and technological importance. Towards this goal, AB diblock copolymers have been studied in depth and it has been shown that adding more blocks and functional groups increases architectural and functional complexity and can lead to more exotic self-assembled morphologies.

Graphical abstract: Synthesis of block polymer miktobrushes

In this study, Lodge and Hillmyer reported an innovative synthetic strategy towards a wide compositional range of structurally well defined “miktobrush” block terpolymers, m-A(BC)_n obtained using rather mild and facile reaction conditions with three separate polymer building blocks. The copolymers were synthesized utilizing the alternating radical copolymerization of two hydrophobic and incompatible macromonomer (MM) building blocks; a maleimide (MI) end functionalized poly(methyl-caprolactone) block (MI-PMCL) or ‘C’ and a styrene (Sty) end functionalized poly(perﬂuoro propylene oxide) block (Sty-PFPO) or ‘F’. Polymerizations were mediated by a poly(ethylene oxide) (PEO) functionalized reversible addition–fragmentation chain transfer (RAFT) agent (PEO–CTA) or ‘O’ to control the chain growth of the MMs from the O block to form O(CF)_n “miktobrush” terpolymers. The synthesis of a range of well deﬁned m-O(CF)_n terpolymers with various compositions was achieved by simply changing the feed of MMs. This new strategy offers a powerful route towards a block polymer architecture that can enable the formation of multi-domain hierarchical nanostructures with features on multiple length scales due to the incompatibility and unique connectivity of the building blocks incorporated.

Synthesis of block polymer miktobrushes by Adam O. Moughton, Takanori Sagawa, William M. Gramlich, Myungeun Seo, Timothy P. Lodge, and Marc A. Hillmyer, Polym. Chem., 2013, 4, 166-173.

Julien Nicolas is a guest web-writer for Polymer Chemistry. He currently works at Univ. Paris-Sud (FR) as a CNRS researcher

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Paper of the week: In situ stereocomplexing polymerization of methyl methacrylate

17 Dec 2012

Stereocomplex poly(methyl methacrylate), sc-PMMA, is a crystalline material formed via van der Waals interactions between diastereomeric, isotactic (it) and syndiotactic (st), PMMA chains. It represents a rare example of helical supramolecular structures derived from a commodity polymer and is typically obtained in a 1/2 it/st ratio either in the solid state, when annealed, or in suitable solvents, when crystallized. In this study, Chen and co-workers hypothesized that, with the advent of stereospeciﬁc and living coordination polymerization by chiral metallocene catalysts, it is possible to combine the synthesis of highly stereoregular PMMAs with the fabrication of their crystalline stereocomplex into a one-step procedure, thereby producing such important crystalline materials in a rapid and cost/energy-saving fashion.

Graphical abstract: In situ stereocomplexing polymerization of methyl methacrylate by diastereospecific metallocene catalyst pairs

The authors demonstrate the ﬁrst in situ stereocomplexing polymerization of MMA using a pair of diastereospeciﬁc coordination polymerization catalysts for rapid, high-yield, ambient-temperature production of crystalline sc-PMMA. The diastereospeciﬁc catalyst pair is conveniently generated by in situ activation of a mixture of C2- and Cs -ligated metallocene bis(ester enolate)s with [Ph₃C][B(C₆F₅)₄], which is highly active, stereospeciﬁc, and controlled for coordination–addition polymerization of MMA. The isotactic/syndiotactic (it/st) composition of the sc-PMMA materials can be modulated by simply adjusting the relative ratio of the diastereospeciﬁc catalysts. The dynamic light scattering (DLS) results of the in situ stereocomplexing polymerization by a diastereospeciﬁc catalyst pair, obtained by monitoring the reaction in real time with DLS, indicate that stereocomplexation occurs as the diastereomeric PMMA chains are continuously growing. The presence of nanocages such as POSS and C60, which can be encapsulated by st-PMMA, in the stereocomplexing MMA polymerization system can completely disrupt or have no effect on the stereocomplexation, or enable both stereocomplexation and inclusion complexation processes to occur, depending on the type of nanocage employed.

In situ stereocomplexing polymerization of methyl methacrylate by diastereospeciﬁc metallocene catalyst pairs by Nicole C. Escudé, Yalan Ning and Eugene Y.-X. Chen, Polym. Chem., 2012, 3, 3247-3255.

Julien Nicolas is a guest web-writer for Polymer Chemistry. He currently works at Univ. Paris-Sud (FR) as a CNRS researcher

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Paper of the week: Necklace- and donut-like poly(propylene imine) glycodendrimers

12 Dec 2012

Over the past 30 years, dendrimers have attracted great attention in plenty of studies stimulated by the high symmetry and monodispersity of these branched macromolecules with well-deﬁned size and shape. Today, these dendritic structures are tailor-made for achieving speciﬁc properties and for potential applications e.g. in bionanotechnology. In this context, one pivotal key issue is the indispensable use of non-covalent interactions and forces for establishing (self-)assembled and self-organized 0D, 1D, 2D and 3D structures. The understanding and control of these non-covalent interactions is also essential for successful application of functional dendrimers in (bio-)medical applications.

Graphical abstract: Self-assembly of poly(propylene imine) glycodendrimers: role of aromatic interactions in the formation of necklace- and donut-like nanostructures

In this study, the authors reported on the formation of necklace- and donut-like structures of water-soluble glycodendrimers bearing a small number of phenyl units as a time-dependent process in aqueous solution starting from self-assembled glycodendrimers to higher hierarchically assembled structures initially triggered by ultrasound treatment. For this study, they designed and synthesized new spherical poly(propylene imine) dendrimer structures by introducing on their peripheral amino groups: (i) hydrophilic bio-tolerable oligosaccharide units (maltose) and (i) hydrophobic groups (adamantyl or phenyl) capable of modifying the physical properties of these glycodendrimers. The glyco-conjugation of dendritic polyamines enabled the authors to enhance the water solubility and biocompatibility of the nanoconstructs which makes them potentially useful as drug delivery systems, therapeutic agents and artiﬁcial tubulating proteins.

Self-assembly of poly(propylene imine) glycodendrimers: role of aromatic interactions in the formation of necklace- and donut-like nanostructures by Marco Paolino, Franka Ennen, Hartmut Komber, Mihaela Cernescu, Andrea Cappelli, Bernhard Brutschy, Brigitte Voit and Dietmar Appelhans, Polym. Chem., 2012, 3, 3239-3242.

Julien Nicolas is a guest web-writer for Polymer Chemistry. He currently works at Univ. Paris-Sud (FR) as a CNRS researcher

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Paper of the week: Dynamic supramolecular poly(isobutylene)s for self-healing materials

03 Dec 2012

Polymers with self-healing or self-repairing properties have gained increasing importance in the past years, often relying on capsule-based concepts, mechanophores and supramolecular concepts. In all cases the basic concept of such materials relies on the use of crosslinking processes which enables repair of a mechanically induced damage by subsequent network-formation. Based on recent observations of hydrogen-bonded supramolecular poly(isobutylene)s (PIBs), where clustering effects were observed due to the interplay of supramolecular association and microphase separation between the polar hydrogen-bonding moieties and the non-polar PIB chains, the authors sought to systematically investigate the clustering and potential use of hydrogen-bonded PIBs for self-healing materials.

Graphical abstract: Dynamic supramolecular poly(isobutylene)s for self-healing materials

Mono- and bifunctional supramolecular PIBs bearing hydrogen-bonding motifs (barbituric acid or a Hamilton wedge) were prepared by a combination of living carbocationic polymerization (LCCP) and azide–alkyne ‘‘click’’ reactions to investigate their dynamics and self-healing behaviour. Temperature-dependent rheology in the melt revealed thermoreversible formation of supramolecular clusters. Stoichiometric mixing of the polymers by solution blending affected the extent of clustering by specifically interacting barbituric acid/Hamilton wedge moieties. Frequency-dependent measurements on bifunctional barbituric acid functionalized PIBs revealed a strong rubbery plateau and terminal flow, caused by the formation of dynamically bridged clusters. Small discs of these polymers showed self-healing at room temperature after being cut and brought into contact at the fractured surface.

Dynamic supramolecular poly(isobutylene)s for self-healing materials by Florian Herbst, Sebastian Seiffert and Wolfgang H. Binder, Polym. Chem., 2012, 3, 3084-3092.

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Paper of the week: Single chain polymeric nanoparticles as compartmentalised sensors

27 Nov 2012

The unique physical properties of supramolecular polymers resulted in a myriad of potential applications ranging from electronics to healthcare and high performance materials. The large spectrum of available self-assembling molecules allows the properties of supramolecular polymers to be tuned to specific requirements of the desired applications. It has been recently shown that linear polymers grafted with non-covalent (or dynamic covalent) interacting groups lead, under selected conditions, to the folding of single polymeric chains into what are now termed single chain polymeric nanoparticles (SCPNs). Due to the unique properties of SCPNs, these well-defined nanometer-sized objects are actively investigated for use in advanced applications in low viscosity coatings, catalytic systems and nanomedicine.

Graphical abstract: Single chain polymeric nanoparticles as compartmentalised sensors for metal ions

In this context, Palmans and co-workers envisionned chemosensing of metal ions as an interesting application of SCPNs. The authors prepared 3,3′-bis(acylamino)-2,2′-bipyridine substituted benzene-1,3,5-tricarboxamide (BiPy-BTA) grafted polynorbornene polymers. The polymers fold intramolecularly via p–p interactions into fluorescent, compartmentalised particles of nanometer-size. Spectroscopic and light scattering techniques show that the compact conformation of the folded polymer is affected by increasing the BiPy-BTA functionalisation degree and by changing the solvent polarity. Changes in the conformation are accompanied by changes in the fluorescence intensity. Due to the affinity of the BiPy units for metal ions such as copper, the particles obtained are effective sensors for these metals. The compartmentalisation of the binding motifs in SCPNs proves to be advantageous in sensor applications of these particles.

Single chain polymeric nanoparticles as compartmentalised sensors for metal ions by Martijn A. J. Gillissen, Ilja K. Voets, E. W. Meijer and Anja. R. A. Palmans, Polym. Chem., 2012, 3, 3166-3174.

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Paper of the week: Role of multitopicity in hydrogen bonded supramolecular polymers

13 Nov 2012

Hydrogen bonding interactions in aqueous media are often very weak because of the competition from water molecules, but they can still have a decisive effect on self-assemblies when used in combination with other interactions. In the case of amphiphiles with a hydrophobic part made from flexible alkyl chains, the introduction of hydrogen bonds within the hydrophobic domains through urea groups has been shown to dramatically increase the viscosity of aqueous solutions, and to enable self-sorting between amphiphiles of distinct structures. Another popular approach to synthesise viscous solutions or gels consists in decorating water soluble high molar mass polymers with hydrophobic groups.

Graphical abstract: Hydrogen bonded supramolecular polymers in protic solvents: role of multitopicity

In this article, Bouteiller and co-workers investigated the properties of systems combining both design elements, i.e. macromolecules with hydrophobic groups able to form very long anisotropic hydrophobic domains. A strong influence of both the number of associative groups per chain and the polydispersity has been demonstrated. In water, where the interactions between stickers are strong, the monomer self-assembles into filaments, but all other compounds with more than one sticker per chain are insoluble. In methanol, where the interactions between stickers are weaker, neither the monomer nor the monodispersed dimer is assembled, whereas polydispersed chains with an average number of stickers per chain of 2 or 3 self-assemble into filaments, leading to macroscopic gelation.

Hydrogen bonded supramolecular polymers in protic solvents: role of multitopicity by Marion Tharcis, Thomas Breiner, Joël Belleney, François Boué and Laurent Bouteiller, Polym. Chem., 2012, 3, 3093-3099.

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Paper of the week: Fluorescence resonance energy transfer in recognition-mediated polymer-quantum dot assemblies

05 Nov 2012

Graphical abstract: Fluorescence resonance energy transfer in recognition-mediated polymer-quantum dot assemblies

Organization of nanoparticles (NPs) into morphologically controlled and organised structures is a central issue for bottom-up fabrication of functional devices in optoelectronics, sensing, catalysis and medicine. Directed host–guest assembly of NPs into polymer matrices is an effective route to form structured NP assemblies with advantageous optical, electronic, magnetic, and mechanical properties. In this article, Cooke, Rotello and co-workers reported recognition mediated assembly of ZnSe quantum dots (QDs) with a chromophore-functionalized polymer, facilitating fluorescence resonance energy transfer (FRET) from QDs to the chromophore. The authors designed and synthesized a polyfunctional copolymer featuring a solubilising methyl methacrylate (MMA) element, a diamidopyridine (DAP) recognition element and a flavin (Fl) chromophore. Thymine functionalized ZnSe QDs (Thy-QDs) were used as the guest in the assembly. Due to the spectral overlap and close proximity of the QDs and flavin units in the assembly, FRET was observed from QDs to flavin. This methodology of producing self-assembled structures both in solution and solid state provides a powerful tool for the creation of highly structured multifunctional materials and devices.

Fluorescence resonance energy transfer in recognition-mediated polymer-quantum dot assemblies by Vikas Nandwana, Brian Fitzpatrick, Qian Liu, Kyril M. Solntsev, Xi Yu, Gülen Yesilbag Tonga, Serkan Eymur, Murat Tonga, Graeme Cooke and Vincent M. Rotello, Polym. Chem. 2012, 3, 3072-3076.

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Paper of the week: Towards ionic-liquid containing polymers

29 Oct 2012

Graphical abstract: Mild and efficient bromination of poly(hydroxyethyl acrylate) and its use towards ionic-liquid containing polymers

Ionic liquids (ILs) have been of widespread use in the world of chemical synthesis for two decades as substitutes for classical solvents, but it is only recently that IL polymers have raised interest in the field of materials sciences. In this context, their unique properties have been taken advantage of in various applications dealing with electric charge transportation. However, the direct controlled polymerization of IL monomers is not straightforward. In this communication, Monnereau and co-workers reported a simple two-step methodology to prepare IL-containing polymers. Their approach relies on a key hydroxy-to-bromine substitution on poly(hydroxyethyl acrylate), followed by the addition of a nucleophile on the resulting polymer. This constitutes an unprecedented simple and quite versatile approach towards the synthesis of a variety of monodisperse ionic liquid containing polymers by atom-transfer radical polymerization (ATRP).

Mild and efficient bromination of poly(hydroxyethyl acrylate) and its use towards ionic-liquid containing polymers

Vinu Krishnan Appukuttan, Anais Dupont, Sandrine Denis-Quanquin, Chantal Andraud and Cyrille Monnereau

Polym. Chem. 2012, 3, 2723-2726.

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Paper of the week: Biocompatible and degradable polymers for biomedical applications

22 Oct 2012

Graphical abstract: Biocompatible and degradable poly(2-hydroxyethyl methacrylate) based polymers for biomedical applications

Poly(2-hydroxyethyl methacrylate) (PHEMA) is a widely used and researched biocompatible polymer. However, PHEMA is neither hydrolysable nor enzymatically degradable. Radical-ring-opening copolymerization of cyclic ketene acetals such as 2-methylene-1,3-dioxepane (MDO) and 5,6-benzo-2-methylene-1,3-dioxepane (BMDO) with vinyl monomers has been a promising method for introducing degradable ester linkages onto the C–C polymer backbones. In this article, Agarwal and co-workers reported the synthesis of degradable and less toxic PHEMA with ester linkages in the backbone by radical copolymerization with cyclic ketene acetal. The copolymers were hydrolytically degradable under basic conditions and also showed surface and bulk degradation using macrophages. The authors also demonstrated promising positive results for the use of such polymers as sustained drug delivery systems.

Biocompatible and degradable poly(2-hydroxyethyl methacrylate) based polymers for biomedical applications by Yi Zhang, Dafeng Chu, Mengyao Zheng, Thomas Kissel and Seema Agarwal Polym. Chem. 2012, 3, 2752-2759.

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Paper of the week: X-linked core-corona nanoparticles

02 Oct 2012

Graphical abstract: In situ formation of crosslinked core–corona polymeric nanoparticles from a novel hyperbranched core

A facile approach for the preparation of well-controlled crosslinked core–corona (CCC) nanoparticles is described. Firstly, a core containing multiple initiating sites was generated by deactivation enhanced atom transfer radical homopolymerisation (DE-ATRP) of divinylbenzene (DVB). Then, the multiple halide initiating sites on this hyperbranched polyDVB core were used to initiate linear chains of methyl methacrylate (MMA) via ATRP. During the second step, the pendant vinyl groups within the core were consumed, leading to generation of a crosslinked nanogel core within the final polymer structures isolated, whilst linear arms (corona) were simultaneously growing from the periphery. The structure of the resulting CCC nanoparticles was confirmed using ¹H NMR spectroscopy, gel permeation chromatography equipped with MALLS (GPC-MALLS), dynamic light scattering (DLS) and atomic force microscopy (AFM).

In situ formation of crosslinked core–corona polymeric nanoparticles from a novel hyperbranched core
Yu Zheng, Kristofer J. Thurecht, Xinyong Chen, Clive J. Roberts, Derek J. Irvine, Steven M. Howdle and Wenxin Wang
Polym. Chem., 2012, 3, 2807-2814.

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Polymer Chemistry Blog

Archive for the ‘Paper of the Week’ Category

Paper of the week: Block polymer miktobrushes

Paper of the week: In situ stereocomplexing polymerization of methyl methacrylate

Paper of the week: Necklace- and donut-like poly(propylene imine) glycodendrimers

Paper of the week: Dynamic supramolecular poly(isobutylene)s for self-healing materials

Paper of the week: Single chain polymeric nanoparticles as compartmentalised sensors

Paper of the week: Role of multitopicity in hydrogen bonded supramolecular polymers

Paper of the week: Fluorescence resonance energy transfer in recognition-mediated polymer-quantum dot assemblies

Paper of the week: Towards ionic-liquid containing polymers

Paper of the week: Biocompatible and degradable polymers for biomedical applications

Paper of the week: X-linked core-corona nanoparticles

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