Polymer Chemistry Blog

Conjugated aromatic polymers have attracted great attention since 1970s. Myriad of studies have been reported on five-membered heterocycles containing polymers such as polypyrroles, polythiophenes and their derivatives due to their susceptible electronic and optical properties. Recent studies showed that furan containing polymers have some priorities over thiophene based ones for the application of polymer organics in advanced technological applications. For instance, the greater electron withdrawing ability of furan is capable of reducing the HOMO energy level of the D parts in the solar cells, which results in the high open circuit voltage.

Cihaner, Onal and their coworkers have designed and synthesized two new furan and benzochalcogenodiazole based monomers, namely 4,7-di(furan-2-yl)benzo[c][1,2,5]-selenadiazole (FSeF) and 4,7-di(furan-2-yl)benzo[c][1,2,5]thiadiazole (FSF), via a donor–acceptor–donor approach. The monomers were electrochemically polymerized via potentiodynamic or potentiostatic methods. The monomers and their polymers exhibited lower oxidation potentials (1.16 V and 1.06 V for monomers; 0.93 V and 0.80 V for polymers vs. Ag/AgCl) and red shifts of the whole dual-band absorption spectra upon moving from S to Se. Intramolecular charge transfer properties of the monomers and the polymers were demonstrated by using electroanalytical and optical methods. Also, the polymers PFSeF and PFSF were multicolored at different redox states and have low band gaps of 1.43 eV and 1.61 eV, respectively.

Furan and benzochalcogenodiazole based multichromic polymers via a donor–acceptor approach by Merve İçli-Özkut, Halil İpek, Baris Karabay, Atilla Cihaner and Ahmet M. Önal Polym. Chem., 2013, 4, 2457-2463

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).

Amphiphilic polymers have been synthesised by controlled free radical polymerisation techniques. These polymers self-assemble into well-defined vesicles in aqueous conditions, enabling encapsulation of a model hydrophilic molecule. The polymeric vesicles show high stability against a range of aqueous conditions with marginal release of cargo, even in the presence of known cell-membrane disruptive polymers such as branched poly(ethylene imine) (b-PEI). This stability allows for inversion of the surface charge of the polymeric vesicles by a simple coating protocol leading to an enhanced uptake by mammalian cells.

Well-defined polymeric vesicles with high stability and modulation of cell uptake by a simple coating protocol Gökçen Yaşayan, Martin Redhead, Johannes P. Magnusson, Sebastian G. Spain, Stephanie Allen, Martyn Davies, Cameron Alexander and Francisco Fernández-Trillo Polym. Chem., 2012, 3, 2596-2604.

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Reversible addition–fragmentation chain transfer (RAFT) polymerization was used to generate well-defined pH-responsive biofunctional polymers as potential ‘smart’ gene delivery systems. A series of five poly(dimethylamino ethyl methacrylate-co-cholesteryl methacrylate) P(DMAEMA-co-CMA) statistical copolymers, with similar molecular weights and varying cholesterol content, were prepared. The syntheses, compositions and molecular weight distributions for P(DMAEMA-co-CMA) were monitored by nuclear magnetic resonance (NMR), solid-state NMR and gel permeation chromatography (GPC) evidencing well-defined polymeric structures with narrow polydispersities. Aqueous solution properties of the copolymers were investigated using turbidimetry and light scattering to determine hydrodynamic diameters and zeta potentials associated with the phase transition behaviour of P(DMAEMA-co-CMA) copolymers. UV-Visible spectroscopy was used to investigate the pH-responsive behaviour of copolymers. Hydrodynamic radii were measured in the range 10–30 nm (pH, temperature dependent) by dynamic light scattering (DLS). Charge studies indicated that P(DMAEMA-co-CMA) polymers have an overall cationic charge, mediated by pH. Potentiometric studies revealed that the buffering capacity and pK_a values of polymers were dependent on cholesterol content as well as on cationic charge. The buffering capacity increased with increasing charge ratio, overall demonstrating transitions in the pH endosomal region for all five copolymeric structures. Cell viability assay showed that the copolymers displayed increasing cytotoxicity with decreasing number of cholesterol moieties. These preliminary results show the potential of these well-defined P(DMAEMA-co-CMA) polymers as in vitro siRNA delivery agents.

Synthesis, self-assembly and stimuli responsive properties of cholesterol conjugated polymers by Sema Sevimli,  Sharon Sagnella,  Maria Kavallaris,  Volga Bulmus and Thomas P. Davis Polym. Chem. 2012, 3, 2057-2069.

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Fast and scalable production of hyperbranched polythioether-ynes was achieved by applying sequential click chemistry (SCC) via couple-monomer methodology (CMM). As a typical example, thiol-halogen click-like reaction employing strong base, KOH and thiol-yne click reaction via UV irradiation were used for precursor preparation and polymerization, respectively. Two series of hyperbranched polythioether-ynes employing two kinds of di-thiols with different reactivity have been prepared within 10 h and characterized with ¹H NMR spectroscopy and gel permeation chromatography. The hyperbranched polymers (HPs) derived from 1,6-hexanedithiol reached high weight-average molecular weight (M_w) of 230500, high weight-average degree of polymerization (DP_w) of 1224 and high degree of branching (DB) of 0.82–0.68. Postmodification of abundant alkyne terminal groups afford HPs with a greatly enhanced DB of 0.96. Heat-initiated polymerization was also attempted. The present study clearly demonstrates the robustness of application of SCC technique in the CMM strategy for fast, scalable preparation of multifunctional HPs.

Fast and scalable production of hyperbranched polythioether-ynes by a combination of thiol-halogen click-like coupling and thiol-yne click polymerization by Jin Han, Bo Zhao, Aijin Tang, Yanqin Gao and Chao Gao Polym. Chem., 2012, 3, 1918-1925

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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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