Archive for the ‘Paper of the Week’ Category

Paper of the week: Stimuli-responsive biocompatible nanovalves

As human health problems are becoming increasingly serious, much research has been focused on nanomaterials with biomedical potential. Especially, stimuli-responsive nanocontainers for drug delivery and release have recently attracted widespread interest in chemical and biological fields. Self-assembled polymeric micelles are traditional nanocontainers that are formed under some certain conditions and destroyed when the environments (pH, temperature, light, etc.) are changed to realize controlled drug release. Other traditional nanocontainers are functionalized inorganic frameworks with large surface areas and suitable pore volumes, such as mesoporous silica nanoparticles (MSNs), metal–organic frameworks (MOFs), and zeolite imidazolate frameworks (ZIFs).

Graphical abstract: Stimuli-responsive biocompatible nanovalves based on β-cyclodextrin modified poly(glycidyl methacrylate)

In their paper, Gao , Yang and co-workers grafted β-cyclodextrins (β-CDs) onto star-shaped poly(glycidyl methacrylate)s (S5-PGMAs) with a straightforward and efficient ring-opening addition of amine groups to result in PGMA–β-CDs, which not only possess good water-solubility and biocompatibility, but also can serve as polymeric supramolecular hosts to form inclusion complexes with suitable guests. They can be easily assembled on the surface of azobenzene-functionalized MSNs via host–guest interactions to obtain MSN@PGMA–β-CD hybrid nanoparticles. The experimental results showed that these types of inorganic–organic hybrid mesoporous nanocomposites possess good cargo encapsulation and release properties, as compared with the simple supramolecular nanovalves with β-CD itself as the gating component, upon activation by light, temperature variation, and competitive binding agents. In addition, the extremely low cytotoxicity of the nanocomposites demonstrated by MTT assay can further broaden their applications in controlled drug release.

Stimuli-responsive biocompatible nanovalves based on β-cyclodextrin modified poly(glycidyl methacrylate) by Qing-Lan Li, Lizhi Wang, Xi-Long Qiu, Yu-Long Sun, Pei-Xi Wang, Yu Liu, Feng Li, Ai-Di Qi, Hui Gao and Ying-Wei Yang Polym. Chem. 2014, 5, 3389-3395.

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

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Paper of the week: Sustainable cycloolefin polymer from pine tree oil for optoelectronics material

Transparent polymers are now recognized by the optoelectronics industry as indispensable materials for plastic lenses and optical storage. Recently, amorphous saturated hydrocarbon polymers consisting of main-chain cyclic units, such as cycloolefin (co)polymers (COC or COP), have demonstrated material superiority and are a popular alternative to conventional transparent polymers, such as poly(methyl methacrylate) (PMMA) and polycarbonate (PC). These alicyclic polymers possess excellent properties, such as high glass-transition temperature (Tg), optical transparency, non-hygroscopicity, and low birefringence. However, there is an increasing demand for materials using natural products, such as plant oil, seed oil, tree resin, tree sap, and other plant chemicals, in place of petroleum-derived industrial materials for better sustainability. Monomers obtained from these renewable natural products to produce bio-based polymers have attracted a lot of attention in addition to conventional natural polymers, such as cellulose. Among the various natural chemicals, terpenes make up a major series of natural compounds which are biologically built up from isoprene units and are available in a large variety.

Graphical abstract: Sustainable cycloolefin polymer from pine tree oil for optoelectronics material: living cationic polymerization of β-pinene and catalytic hydrogenation of high-molecular-weight hydrogenated poly(β-pinene)

In this article, Kamigaito and co-workers cationically polymerized (−)-β-pinene, a major constituent of pine tree oil,  to generate a high-molecular-weight polymer that were subsequently hydrogenated via metal catalysts to give a high-performance, bio-based cycloolefin polymer with an alicyclic backbone. To obtain the high-molecular-weight polymer, the controlled/living cationic polymerization of (−)-β-pinene was investigated by an initiating system, consisting of a protonic acid, a Lewis acid, and an added base, along with an incremental monomer addition technique. These reactions could be performed even at relatively large scales to produce several hundred grams of the polymer, which can be then processed through injection-molding. The synthesized bio-based cycloolefin polymers demonstrated promising potential properties as high performance optical plastics with good processability, low density, high optical transparency, low birefringence, non-hygroscopicity, high mechanical strength, and excellent thermal properties.

Sustainable cycloolefin polymer from pine tree oil for optoelectronics material: living cationic polymerization of β-pinene and catalytic hydrogenation of high-molecular-weight hydrogenated poly(β-pinene) by Kotaro Satoh, Atsuhiro Nakahara, Kazunori Mukunoki, Hiroko Sugiyama, Hiromu Saito and Masami Kamigaito Polym. Chem. 2014, 5, 3222-3230.

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

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Paper of the week: A powerful method for 3D bulk patterning of polymer sheets

Polymer films are ubiquitous in numerous industrial fields such as electronics, biotechnology, optics or portable energy devices. Improving the performances of devices in this broad range of applications most often requires creating 2D- or 3D-structured polymer films in order to combine the material bulk properties and designated interactions with their local environment. For this purpose, methods usually used are based on: (i) phase separation of block copolymers which leads to polymer blend films with an isotropic structure or (ii) radiation-induced graft polymerization to obtain isotropic architecture by an electron beam or γ-ray radiation or an anisotropic structure by swift heavy ion irradiation or by X-rays or Extreme UltraViolet (EUV) light radiation. However, these processes present some limitations such as block copolymer and film synthesis, drastic safety procedures or the high cost of ionising sources.

Graphical abstract: VUV grafting: an efficient method for 3D bulk patterning of polymer sheets

To overcome these drawbacks, Berthelot and co-workers proposed here an innovative process, based on VUV irradiation, which proved efficient not only for surface modification, but also for the bulk modification of industrially relevant polymers such as β-polyvinylidene fluoride (β-PVDF), polyethylene (PE) or fluorinated ethylene propylene (FEP). The authors assumed that VUV irradiation of a PVDF film can induce radical active species at depths up to 50 micrometers, as demonstrated by ESR. Those active species were able to initiate the radical polymerization of a vinylic or acrylate monomer such as acrylic acid through the polymer film, as confirmed by the EDX profile of the film thickness. Similar results were obtained on PE and FEP films, while aromatic polymers such as PET strongly absorbed VUV energy and dissipated it along other pathways. By mixing this process and photolithographic masks, 3D structuration of commercial polymer films was also obtained.

VUV grafting: an efficient method for 3D bulk patterning of polymer sheets by Cecile Baudin, Jean-Philippe Renault, Stephane Esnouf, Serge Palacin and Thomas Berthelot Polym. Chem. 2014, 5, 2990-2996.

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

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Paper of the week: Polyoxalates from biorenewable diols via Oxalate Metathesis Polymerization

Polyoxalates are polymers based on oxalic acid or derivatives and contain the –O(CO)2O– functional group. They have shown a relatively high degradability under aqueous conditions and have been investigated for certain medical applications, such as drug delivery. This facile degradability could also be exploited for alternative applications, such as medical sutures or packaging plastics with diminished environmental impact. Moreover, polyoxalates are readily synthesized from biorenewable resources, a significant sustainability advantage over fossil fuel-based polymers.

Graphical abstract: Polyoxalates from biorenewable diols via Oxalate Metathesis Polymerization

In this study, Garcia and Miller were inspired to develop improved synthetic routes and novel families of polyoxalates, particularly targeting thermal properties that might allow mimicry of  popular packaging thermoplastics. Polyalkylene oxalates and polyarylene oxalates were successfully synthesized via oxalate metathesis polymerization (OMP), a step-growth polymerization that employs acid-catalyzed ester interchange of dimethyl oxalate and a diol in a 1:1 ratio. The process was optimized in the melt and did not require solvents. Aliphatic/aromatic polyoxalate copolymers derived from 1,10- decanediol and resorcinol bis(hydroxyethyl)ether or hydroquinone bis(hydroxyethyl)ether in varying compositions were also prepared and studied. Incorporation of the aromatic diols into the polymer chain generally afforded increased Tg and Tm. Solid-state degradation studies indicated facile water-degradation of the polyoxalates as molecular weights decreased 81-92% over the course of 13 months in humid air.

Polyoxalates from biorenewable diols via Oxalate Metathesis Polymerization by John J. Garcia and Stephen A. Miller Polym. Chem. 2014, 5, 955-961.

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

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Paper of the week: Optimising the enzyme response of a porous silicon photonic crystal

There is a need for devices that can detect various biological species for the development of biotechnology and medical diagnostics. For instance, it is important to measure the activity of enzymes like proteinases released from cells for the understanding of fundamental cell biology and biomedical applications. One class of the proteinases is the matrix metalloproteinases (MMPs) which are known to be released by cells as part of their normal tissue remodelling processes, such as embryonic development and cell migration. Currently, the most common proteinase activity measurements are performed by fluorogenic or calorimetric methods with commercially available proteinase assay kits. Enzymatic responsive polymers have also been developed as sensing elements in biological devices.

Graphical abstract: Optimising the enzyme response of a porous silicon photonic crystal via the modular design of enzyme sensitive polymers

In this work, Gooding and co-workers have demonstrated a generic approach to optimize the sensing capability of porous silicon through a modular polymer conjugation strategy where the surface of the  porous silicon (PSi) was first modified with an antifouling polymer, then an enzyme cleavable link was added which bridged the antifouling polymer and a second sacrificial polymer that was lost upon enzyme cleavage of the peptide. Cleavage of the peptide–polymer network by the appropriate proteinase decreases the average refractive index of the photonic crystal resulting in a change in the reflectivity peak to lower wavelengths (blue-shift). The PSi–polymer constructs were shown to have selectivity towards different MMP enzymes. The approach could easily be tailored for different chemical/biochemical moieties, thus increasing the potential of such smart surfaces for biosensor applications. These structures could be easily expanded for other proteinase enzymes by simply changing the specific peptide sequences.

Optimising the enzyme response of a porous silicon photonic crystal via the modular design of enzyme sensitive polymers by Alexander H. Soeriyadi, Bakul Gupta, Peter J. Reece and J. Justin Gooding Polym. Chem. 2014, 5, 2333-2341.

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

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Paper of the week: Crystallization-driven self-assembly of polyferrocenylsilane diblock copolymers

Extensive research has been performed in the field of block copolymer synthesis and their self-assembly in block-selective solvents in order to provide routes for the design and synthesis of nanostructures with desirable properties. Block copolymers have been self-assembled into a vast range of micellar nanostructures whose morphologies include spheres, tapes and vesicles as well as many other more complex shapes. Recently, investigations into the self-assembly of polyferrocenylsilane (PFS)-containing block copolymers have led to the preparation of cylinders of controlled length. Furthermore, block co-micelles with segmented coronal chemistries can also be prepared through the crystallization-driven self-assembly (CDSA) of one PFS-containing block copolymer from cylindrical micelles of another. To date, the vast majority of studies of the CDSA of PFS block copolymers have focused on examples with a non-polar corona-forming block.

Graphical abstract: Synthesis and crystallization-driven solution self-assembly of polyferrocenylsilane diblock copolymers with polymethacrylate corona-forming blocks

In order to increase the range of coronal chemistries available for CDSA protocols a series of highly asymmetric diblock copolymers comprising a PFS block and a polymethacrylate coblock (poly(tert-butylmethacrylate) (PtBMA), poly(n-butylmethacrylate) (PnBMA), and poly(N,N-dimethylaminoethylmethacrylate) (PDMAEMA), were synthesized by sequential living anionic polymerization. Self-assembly of these block copolymers in acetone yielded cylindrical micelles with a crystalline PFS core and a polymethacrylate corona. The cylindrical micelles were fragmented by sonication and the short micelles were successfully used as “seed initiators” to grow longer monodisperse cylindrical micelles with controlled lengths from added unimers via crystallization-driven living self-assembly. Block co-micelles were also prepared by the sequential addition of unimers with a different coronal block to pre-existing cylinders. These nanostructures could be potentially used as scaffolds for the directed deposition of nanoparticles or for electrostatically-induced organization into hierarchically ordered nanomaterials.

Synthesis and crystallization-driven solution self-assembly of polyferrocenylsilane diblock copolymers with polymethacrylate corona-forming blocks by Nina McGrath, Felix H. Schacher, Huibin Qiu, Stephen Mann, Mitchell A. Winnik and Ian Manners Polym. Chem. 2014, 5, 1923-1929.

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

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Paper of the week: Novel photoinitiators for click chemistry

The emergence of the Click Chemistry concept has led to the identification of a set of highly efficient, reliable and selective reactions that readily meet the demands and desires for the synthesis of new materials. Specifically, the copper catalyzed azide–alkyne cycloaddition (CuAAC) reaction has been prominently established as the ideal click reaction due to its simplicity, orthogonality and regioselectivity relative to other organic reactions. Unlike conventional CuAAC approaches using Cu(I) salts, reducing agents, or copper turnings, a photo-mediated technique for generating Cu(I) in situ affords comprehensive spatial and temporal control of the CuAAC reaction, wherein the generation of Cu(I) is limited to selectively irradiated regions in both time and space. In addition to the spatiotemporal control, the photo-induced CuAAC reaction offers a facile means to control the reaction rate simply by changing the light intensity or photoinitiator concentration.

Graphical abstract: Evaluation and development of novel photoinitiator complexes for photoinitiating the copper-catalyzed azide–alkyne cycloaddition reaction

In this paper, Bowman and co-workers demonstrated both spatial and temporal control over the CuAAC by the photo-induced generation of the active form of the catalyst Cu(I) to initiate the CuAAC reaction. Tertiary aliphatic amine ligands were used as an electron transfer species to reduce Cu(II) upon irradiation while also functioning as an accelerating agent and as protecting ligands for the Cu(I). Moreover, this catalyst system was demonstrated to be effective, adaptable to organic and aqueous media, and highly selective to the CuAAC reaction.

Evaluation and development of novel photoinitiator complexes for photoinitiating the copper-catalyzed azide–alkyne cycloaddition reaction by Abeer A. Alzahrani, Annette H. Erbse and Christopher N. Bowman Polym. Chem. 2014, 5, 1874-1882.

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

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Paper of the week: Voltage-responsive micelles

Stimuli-responsive systems composed of intelligent polymers can undergo physical or chemical changes, such as gel–sol transitions or a change in size or volume, as a response to external stimuli, such as light, pH, temperature, redox reactions and so on. They have attracted much attention for their wide application in the field of medical materials and nano machines. Among the possible stimuli, electrical stimuli are considered to be significantly attractive. The electron transfer reaction is one of the simplest types of chemical reactions, and is reasonably well understood from a theoretical standpoint. When conducting electrical stimuli, a certain magnitude of voltage or current is applied to induce a redox reaction of the host or guest molecules.

Graphical abstract: Voltage-responsive micelles based on the assembly of two biocompatible homopolymers

In this paper, Yuan and co-workers  reported on voltage-responsive micelles based on the assembly of two biocompatible homopolymers, namely; poly(ethylene glycol) homopolymer modified with β-cyclodextrin (PEG–β-CD) and poly(L-lactide) homopolymer modified with ferrocene (PLLA–Fc). Through host–guest interactions between β-CD and Fc, the two homopolymers connect together, forming a non-covalent supramolecular block copolymer PLLA–Fc/PEG–β-CD. PLLA–Fc/PEG–β-CD can further self-assemble to form stable micelles in aqueous solution. Through electrochemical control, a reversible assembly–disassembly transition of this micellar system was realized and voltage-controlled drug release based on this system was also conducted successfully using paclitaxel as the anticancer agent.

Voltage-responsive micelles based on the assembly of two biocompatible homopolymers by Liao Peng, Anchao Feng, Huijuan Zhang, Hong Wang, Chunmei Jian, Bowen Liu, Weiping Gao and Jinying Yuan Polym. Chem. 2014, 5, 1751-1759.

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

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Paper of the week: Variable conformation pH responsive block copolymers for drug delivery

Polymeric carriers offer many advantages for controlled release applications, drug delivery and nanomedicine. These systems need to be water-soluble, non-toxic and non-immunogenic, as well as compatible with serum components. For most applications, polymer based delivery systems must also be capable of being either degraded to harmless breakdown products or eliminated entirely from the body. Furthermore, these carriers need functional groups that allow them to interact with or encapsulate a drug of interest, and preferably should contain recognition motifs, which target disease-related antigens or receptors. Not surprisingly, the combination of these factors is hard to achieve with existing materials, leading to an urgent need for new highly functional and active biomedical polymers.

Graphical abstract: Synthesis and characterization of variable conformation pH responsive block co-polymers for nucleic acid delivery and targeted cell entry

In this article, Vicent, Salmaso, Alexander and co-workers prepared a modular and effective controlled release system, based on polymers designed to respond to the pH-changes that occur in tissues affected by peculiar disease. The individual blocks were composed of (a) permanently hydrophilic chains with neutral functionality and (b) acrylate polymers with weakly basic side-chains. Variation in co-monomer content, molar mass and block ratios/compositions led to a range of pH-responses, manifested through reversible self-assembly into micelles and/or polymersomes. These transitions were tuned to achieve environmental responses in a pH range from 5–7. The ability of the systems assembled with these polymers to act as pH-responsive containers was shown by DNA encapsulation and release studies, and their potential for application as vehicle for drug delivery was proved by cell metabolic activity and cell uptake measurements.

Synthesis and characterization of variable conformation pH responsive block co-polymers for nucleic acid delivery and targeted cell entry by Teresa Matini, Nora Francini, Anna Battocchio, Sebastian G. Spain, Giuseppe Mantovani, Maria J. Vicent, Joaquin Sanchis, Elena Gallon, Francesca Mastrotto, Stefano Salmaso, Paolo Caliceti and Cameron Alexander Polym. Chem. 2014, 5, 1626-1636.

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

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Paper of the week: Facile synthesis of thiol-functionalized amphiphilic polylactide–methacrylic diblock copolymers

Block copolymers based on the same type of monomer (e.g., either vinyl or cyclic monomers) are traditionally prepared using a single “living” polymerization technique. Recently, novel block copolymers with interesting properties have been prepared by combining two or more “living” polymerization chemistries to copolymerize dissimilar monomers. Sequential polymerizations are most commonly used for such syntheses. In principle, simultaneous polymerization can also lead to the synthesis of block copolymers. In practice, there are some examples in the literature for which incompatibility problems have been overcome to combine different polymerization techniques for the synthesis of well-defined block copolymers in a single step.

Graphical abstract: Facile synthesis of thiol-functionalized amphiphilic polylactide–methacrylic diblock copolymers

In this publication, Themistou, Battaglia and Armes reported on the one-pot metal-free ring-opening polymerization (ROP)–reversible addition–fragmentation chain transfer (RAFT) synthesis of biocompatible linear and branched amphiphilic diblock copolymers based on a biodegradable aliphatic polyester (PLA) and methacrylic monomers (such as 2-(dimethylamino)ethyl methacrylate (DMA) or oligo(ethylene glycol) methacrylate (OEGMA)), using a novel hydroxyl-functionalized trithiocarbonate-based chain transfer agent. These amphiphilic diblock copolymers self-assembled in dilute aqueous solution, leading to various copolymer morphologies depending on the block compositions. Two novel disulfide-functionalized PLA-branched block copolymers were also synthesized using simultaneous ROP of LA and RAFT copolymerization of OEGMA or DMA with a disulfide-based dimethacrylate. The disulfide bonds were reductively cleaved using tributyl phosphine to generate reactive thiol groups. Thiol–ene chemistry was utilized for further derivatization with thiol-based biologically important molecules and heavy metals for tissue engineering or bioimaging applications, respectively.

Facile synthesis of thiol-functionalized amphiphilic polylactide–methacrylic diblock copolymers by Efrosyni Themistou, Giuseppe Battaglia and Steven P. Armes Polym. Chem. 2014, 5, 1405-1417.

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

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