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Paper of the Week: Poly(ethylene) brushes grafted to silicon substrates

18 Jul 2012

A poly(glycidyl methacrylate) (PGMA) synthesized by RAFT polymerization was spin-coated onto a silicon substrate to yield, after annealing and rinsing unreacted chains, covalently attached epoxy-containing PGMA pseudo-brushes. A tailor-made ω-amino-poly(ethylene) (M_n = 1040 g mol⁻¹, PDI = 1.3) was then grafted in melt at 130 °C for 24 h by reaction between amine chain-ends and surface-tethered epoxy groups. After discarding unreacted poly(ethylene) chains by sonication and Soxhlet rinsing, the resulting poly(ethylene) brushes were characterized by scanning probe microscopy, water contact angle and neutron reflectivity measurements. The grafting of poly(ethylene) brushes to silicon substrates has thus been demonstrated for the first time and resulted in nanostructured grafted layers with homogeneous surface coverage.

Poly(ethylene) brushes grafted to silicon substrates by Denis Damiron, Jérôme Mazzolini, Fabrice Cousin, Christophe Boisson, Franck D’Agosto and Eric Drockenmuller Polym. Chem., 2012, 3, 1838-1845.

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Paper of the Week: From-syndiotactic-to-isotactic stereogradient polymers

12 Jul 2012

Graphical abstract: From-syndiotactic-to-isotactic stereogradient methacrylic polymers by RAFT copolymerization of methacrylic acid and its bulky esters

Stereogradient polymers are a new class of polymers in which the tacticity continuously changes from one chain end to the other. Such polymers may exhibit special properties or functions that originate from gradual changes in the physical or chemical properties along the polymer backbone. In this article, the synthesis of stereogradient polymers with tacticities that vary from predominantly syndiotactic to highly isotactic was investigated by reversible addition–fragmentation chain transfer (RAFT) copolymerization of bulky methacrylates, such as triphenylmethyl methacrylate (TrMA) and 1-phenyldibezosuberyl methacrylate (PDBSMA) and methacrylic acid (MAA) in both non-polar and polar solvents. With the differing reactivities and stereospecificities or TrMA and MAA, the isotacticity of the resulting copolymer gradually increased from 11% to nearly 100% along the polymer chain. Interestingly, the reported method can be applied to the synthesis of various stereogradient poly(MAA)s or polymethacrylates by postpolymerization modification.

From-syndiotactic-to-isotactic stereogradient methacrylic polymers by RAFT copolymerization of methacrylic acid and its bulky esters by Kenji Ishitake , Kotaro Satoh , Masami Kamigaito and Yoshio Okamoto, Polym. Chem., 2012, 3, 1750-1757.

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Paper of the Week: One pot synthesis of sugar sensors

05 Jul 2012

Graphical abstract: Direct nitroxide mediated (co)polymerization of 4-vinylphenylboronic acid as route towards sugar sensors

The glucose blood level should be carefully monitored in people suffering from diabetes mellitus. In this view, a wide variety of glucose sensing molecules have been developed in the recent decades, based on boronic acid functionalized dyes that change colour or emission in the presence of glucose. The incorporation of boronic acid moieties as polymer side chains

indeed results in glucose responsive polymers that are insoluble in the absence of glucose and are solubilised in the presence of glucose due to the higher polarity of the stabilized tetragonal anionic boronic acid form. The present work of Hoogenboom and co-workers aims at developping a simple macromolecular synthesis procedure for the preparation of boronic acid containing polymers, making them accessible to a wide range of polymer scientists, beyond polymer chemists. They used a combination of commercial products; the unprotected 4-vinylphenylboronic acid (4-VBA) and the BlocBuilder alkoxyamine initiator for nitroxide mediated polymerization (NMP). The developed NMP method opens up new avenues towards 4-VBA containing polymers to evaluate glucose responsivity of various copolymers, including block copolymers for autonomous insulin delivery upon increasing glucose concentration.

Direct nitroxide mediated (co)polymerization of 4-vinylphenylboronic acid as route towards sugar sensors by Gertjan Vancoillie , Simon Pelz , Elisabeth Holder and Richard Hoogenboom, Polym. Chem., 2012, 3, 1726-1729.

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Paper of the Week: Remotely triggered drug release from magnetic nanoparticles

26 Jun 2012

Graphical abstract: Thermoresponsive polymer brush-functionalized magnetic manganite nanoparticles for remotely triggered drug release

Over the past decade, considerable interest has been devoted to the development of a variety of nanoparticle-based drug delivery systems for nanomedicine. A large number of drug release strategies have been proposed and may be classified according to the nature of the stimulus used to trigger the process. In this context, Lecommandoux, Schatz and co-workers reported on the design of a thermoresponsive hybrid system for drug delivery purposes by modifying the surface of silica-coated magnetic lanthanum strontium manganite nanoparticles with adsorbed polyether-b-poly(L-lysine) block copolymers. They demonstrated that the thermoresponsiveness of the assemblies was controlled by the ethylene oxide/propylene oxide ratio in the polymer brush and the corresponding LCST of the polyether blocks. The polarity of the polymer layer was also varied to maximize the encapsulation efficiency of a moderately hydrophobic drug like doxorubicin. Eventually, the release of doxorubicin through the synergistic effects of thermoresponsive polymer brushes and magnetically induced heating was demonstrated.

Thermoresponsive polymer brush-functionalized magnetic manganite nanoparticles for remotely triggered drug release by Stéphanie Louguet, Bérengère Rousseau, Romain Epherre, Nicolas Guidolin, Graziella Goglio, Stéphane Mornet, Etienne Duguet, Sébastien Lecommandoux and Christophe Schatz, Polym. Chem., 2012, 3, 1408-1417.

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Paper of the Week: Functional block copolymer nanoparticles

19 Jun 2012

Graphical abstract: Functional block copolymer nanoparticles: toward the next generation of delivery vehicles

The design of efﬁcient drug delivery vehicles has been a long standing challenge in polymer and materials science. A variety of polymeric platforms have been developed in recent years based on an array of different structures including micelles, dendrimers, hydrogels and encapsulant nanoparticle. Exploiting the concept of dispersion self-assembly of soft materials in the drug delivery arena requires the incorporation of multiple functionalities into a judiciously designed BCP platform. In this paper, Hawker and co-workers reported the design of nanoparticles made of well-deﬁned block copolymers (BCPs) containing an alkyne-functional, biodegradable polylactide (PLA) conjugated with azide-functional coumarin dyes, as a model drug, via copper catalyzed azide alkyne cycloaddition ‘click’ chemistry. Self-assembled nanoparticles with internal nanophase-separated morphologies were accessed by carefully controlling the composition of the BCPs and release of the covalently attached model payload was shown to occur under physiological conditions via the degradation of the PLA scaffold. These results demonstrated the potential of self-assembled nanoparticles as modular delivery vehicles with multiple functionalities, nanostructures, and compartmentalized internal morphology.

Functional block copolymer nanoparticles: toward the next generation of delivery vehicles by Maxwell J. Robb, Luke A. Connal, Bongjae F. Lee, Nathaniel A. Lynd and Craig J. Hawker, Polym. Chem., 2012, 3, 1618-1628.

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Paper of the Week: Copolymerization of isoprene and hydroxyl containing monomers by controlled radical and emulsion methods

12 Jun 2012

Graphical abstract: Copolymerization of isoprene and hydroxyl containing monomers by controlled radical and emulsion methods

Polyisoprene (PI) is an interesting backbone material for graft copolymer synthesis. Isoprene can be renewably sourced and polymerized through a variety of methods. Hydroxyl functionalized PI is interesting as it allows for the synthesis of polylactide graft copolymers with a rubbery backbone, which can be quite tough materials as compared to the brittle poly(lactic acid) (PLA) homopolymer. In an effort to develop a hydroxyl functionalized PI macroinitiator, the authors investigated RAFT copolymerizations of isoprene with 2-methylenebut-3-en-1-ol (IOH) and with commercially available, hydroxyl containing monomers 2-hydroxyethyl acrylate (HEA) and 2-hydroxyethyl methacrylate (HEMA). The monomer IOH, structurally similar to isoprene, exhibited favorable kinetics towards copolymerization and copolymerized with isoprene in a rather random manner, producing P(I-co-IOH) macroinitiators with hydroxyl content close to that which was fed into the system. Additionally, IOH was copolymerized with isoprene in an emulsion process at room temperature. The hydroxyl containing isoprene copolymers were also able to undergo subsequent reactions efﬁciently to produce PLA graft copolymers.

Copolymerization of isoprene and hydroxyl containing monomers by controlled radical and emulsion methods by William M. Gramlich , Grayce Theryo and Marc A. Hillmyer Polym. Chem., 2012, 3, 1510-1516.

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Paper of the Week: Programmable digital nonvolatile memory

06 Jun 2012

Graphical abstract: Programmable digital nonvolatile memory behaviors of donor–acceptor polyimides bearing triphenylamine derivatives: effects of substituents

The world market for nonvolatile memory devices has grown rapidly as the demand for mobile devices has increased. The high-performance polymers based on aromatic polyimides (PIs) under development yield many advantages and several PIs have been introduced as the active materials in nonvolatile memory devices. The authors reported here the effects of substituents on the electrical memory characteristics of poly(4,4′-aminotriphenylene hexafluoroisopropylidenediphthalimide) (6F-TPA PI) analogs prepared from two different triphenylamine (TPA) derivatives. These PIs exhibited various types of memory behavior, namely, unipolar WORM and ON/OFF switching-type memory and bipolar ON/OFF switching type memory, depending on the incorporated substituents. The underlying switching mechanism was investigated, and the interfaces between the PI films and the metal electrodes in devices were examined.

Programmable digital nonvolatile memory behaviors of donor–acceptor polyimides bearing triphenylamine derivatives: effects of substituents by Taek Joon Lee, Yong-Gi Ko, Hung-Ju Yen, Kyungtae Kim, Dong Min Kim, Wonsang Kwon, Suk Gyu Hahm, Guey-Sheng Liou and Moonhor Ree Polym. Chem., 2012, 3, 1276-1283.

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Paper of the Week: Copper mediated controlled radical polymerization in a continuous tubular reactor

30 May 2012

Graphical abstract: Copper mediated controlled radical polymerization of methyl acrylate in the presence of ascorbic acid in a continuous tubular reactor

Single electron transfer-living radical polymerization (SET-LRP) has been recently proposed as a “variant” of the originally-developed atom transfer radical polymerization (ATRP). There has been very little research done, however, combining SET-LRP with reducing agents. In this view, Cunningham and co-workers reported an innovative design for a flow reactor for the continuous production of uniform polymer with high livingness using SET-LRP, improving upon the initial concept. Instead of using copper tubing to construct the entire reactor, a short copper coil was used to initiate polymerization and generate soluble copper species. The bulk of the reaction then took place in inert stainless steel tubing, using ascorbic acid as a reducing agent to drive the catalytic cycle and mediate the polymerization. Polymerizations were conducted at ambient temperature with 30 wt% DMSO as solvent, producing well defined living polymer at a steady state conversion of 78% for a residence time of 62 min. Chain extensions using outlet polymer solutions were well-controlled and proceeded to high conversion in a short period of time, with a final concentration of 10 ppm of residual copper. The results illustrate the significant potential of using a continuous tubular reactor with ascorbic acid as a reducing agent as an efficient means to scale-up production of well controlled polyacrylics and other multiblock copolymers.

Copper mediated controlled radical polymerization of methyl acrylate in the presence of ascorbic acid in a continuous tubular reactor by Nicky Chan, Michael F. Cunningham and Robin A. Hutchinson Polym. Chem., 2012, 3, 1322-1333.

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Paper of the Week: Glycopolymer–peptide bioconjugates with antioxidant activity

21 May 2012

Graphical abstract: Glycopolymer–peptide bioconjugates with antioxidant activity via RAFT polymerization

Peptide/protein–polymer bioconjugates have attracted increasing interest as they have numerous potential applications in biotherapeutics, biotechnology, and nanotechnology. In their paper, Liu and co-workers employed reversible addition–fragmentation chain transfer radical (RAFT) polymerization to design poly(2-(2,3,4,6-tetra-O-acetyl-b-D-glucosyloxy)ethyl

methacrylate) (PAcGlcEMA) polymers end-functionalized with the tripeptide reduced glutathione (GSH). The resulting PGlcEMA-GSH bioconjugate exhibited high affinity for Concanavalin A and significant antioxidant activity.

The specific recognition of targeting glucose moieties and antioxidant ability of GSH make peptide–glycopolymer bioconjugate PGlcEMA-GSH a suitable candidate for antioxidant delivery systems, biomimetics and biodetection.

Glycopolymer–peptide bioconjugates with antioxidant activity via RAFT polymerization by Haiting Shi, Li Liu, Xiaobei Wang and Jingyi Li Polym. Chem., 2012, 3, 1182-1188.

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Paper of the Week: Measurement platform for monomer reactivity ratios

17 May 2012

Graphical abstract: A robust and high-throughput measurement platform for monomer reactivity ratios from surface-initiated polymerization

Knowledge of monomer reactivity ratios provides the necessary insight to control and predict the monomer sequence; however, these kinetic parameters are often time-consuming and difﬁcult to accurately measure. In their study, Beers and co-workers reported a robust approach to measure monomer reactivity ratios using surface-initiated copolymerization and XPS as a synthesis and characterization toolset. For the range of monomer pairs investigated, reactivity ratios obtained from the non-linear least squares evaluation of XPS copolymer composition data are reproducible and are in good agreement with bulk reactivity ratios obtained by traditional NMR analysis. Additionally, they have developed and demonstrated a high-throughput approach to measure reactivity ratios using a single substrate exhibiting a gradient in copolymer brush composition. The high-throughput approach signiﬁcantly reduces the time and effort required to generate reliable and reproducible point estimates of reactivity ratios, and these values are in good agreement with values obtained from both the discrete statistical copolymer brush and classical bulk analytical methods.

A robust and high-throughput measurement platform for monomer reactivity ratios from surface-initiated polymerization by Derek L. Patton, Kirt A. Page, Emily A. Hoff, Michael J. Fasolka and Kathryn L. Beers Polym. Chem., 2012, 3, 1174-1181.

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Polymer Chemistry Blog

Archive for the ‘Paper of the Week’ Category

Paper of the Week: Poly(ethylene) brushes grafted to silicon substrates

Paper of the Week: From-syndiotactic-to-isotactic stereogradient polymers

Paper of the Week: One pot synthesis of sugar sensors

Paper of the Week: Remotely triggered drug release from magnetic nanoparticles

Paper of the Week: Functional block copolymer nanoparticles

Paper of the Week: Copolymerization of isoprene and hydroxyl containing monomers by controlled radical and emulsion methods

Paper of the Week: Programmable digital nonvolatile memory

Paper of the Week: Copper mediated controlled radical polymerization in a continuous tubular reactor

Paper of the Week: Glycopolymer–peptide bioconjugates with antioxidant activity

Paper of the Week: Measurement platform for monomer reactivity ratios

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