pinecone/core-2020-05-10-deduplication huggingface dataset:
Vertical crowdsourcing in Russia: balancing governance of crowds and state-citizen partnership in emergency situations

Crowdsourcing can be analyzed not only as a mechanism for empowerment, but also as operating a form of control over volunteers. This article applies Foucault's notion of governmentality to examine relations between traditional governmental institutions and users of crowdsourcing platforms in Russia. Through a comparative analysis of two emergency volunteering portals, Dobrovoletz, and Rynda.org, we describe “vertical crowdsourcing” as a strategy by traditional (government affiliated) actors to use crowdsourcing platforms to govern and control volunteers. This is in contrast to horizontally organized, or ground-up understandings of crowd-volunteering platforms. Two alternative discourses around the role of crowd members are further discussed: volunteers as actors who can contribute resources to the achievement of a common goal, and the crowd as a threat to central government that needs to be controlled
Secondary Crystallization of Isotactic Polystyrene

When isotactic polystyrene (i-PS) is crystallized from the melt or from the glassy state at rather large supercooling an additional melting peak appears on the curve during scanning in a differential calorimeter. The overall rate of crystallization deduced from the total peak areas as a function of crystallization time did not fit the Avrami equation well. When we omit the area of the additional melting peak in the kinetic analysis a much better fit is obtained. We also observed that no lamellar thickening occurs during isothermal crystallization. In view of the low degree of crystallinity of i-PS these results lead to the idea that a secondary crystallization process takes place within the amorphous parts of the spherulites resulting in this additional melting peak on the DSC curve. The large supercooling needed and the increase in peak area with increasing molecular weight make us suppose that intercrystalline links are probably responsible for the additional melting peak of bulk-crystallized i-PS. Electron microscopic studies of surface replicas of i-PS support this view.
Cure kinetics of ring-opening metathesis polymerization of dicyclopentadiene

The cure kinetics of polydicyclopentadiene (pDCPD) prepared by ring-opening metathesis polymerization with three different concentrations of Grubbs' catalyst was examined using differential scanning calirimetry (DSC). The experimental data were used to test several different phenomenological kinetic models. The data are best modeled with a "model-free" isoconversional method. This analysis reveals that the activation energy increases significantly for degree of cure greater than 60%. Catalyst concentration is shown to have a large effect on the cure kinetics.published or submitted for publicationis peer reviewe
Proton-Conducting Polymers Based on Benzimidazoles and Sulfonated Benzimidazoles

A sulfonated derivative of polybenzimidazole is reported, and its properties\ud
are analyzed in comparison with related polybenzimidazole proton-conducting materials.\ud
Poly(2,5-benzimidazole), poly(m-phenylenebenzobisimidazole), and poly[m-(5-\ud
sulfo)-phenylenebenzobisimidazole] were prepared by condensation of the corresponding\ud
monomers in polyphosphoric acid. Several adducts of these polymers with phosphoric\ud
acid were prepared. The resulting materials were characterized by chemical\ud
analysis, Fourier transform infrared spectroscopy, and thermogravimetric analysis;\ud
also, the dc conductivity of doped and undoped derivatives was measured. Similar to\ud
what has been observed for the commercial polybenzimidazole polymer (also examined\ud
here for comparison), the title polymers exhibit high thermal stability. Furthermore,\ud
their doping with phosphoric acid leads to a significant increase in conductivity from\ud
less than 10211 Scm21 for the undoped polymers to 1024 Scm21 (both at roomtemperature)\ud
for their acid-loaded derivativesmThis work was funded by Centro de Investigación Científica y Tecnológica (CICYT, Spain) (MAT98-0807-\ud
C02-02). The authors thank the Ministry of Science and\ud
Technology (Spain) for a predoctoral fellowship awarded\ud
to J. A. Asensio.Peer reviewe
Poly(butylene terephthalate-co-5-tert-butyl isophthalate) Copolyesters: Synthesis, Characterization and Properties

A series of poly(butylene terephthalate) copolyesters containing 5-tert-butyl isophthalate units up to 50%-mole, as well as the homopolyester entirely made of these units, were prepared by polycondensation from the melt. The microstructure of the copolymers was determined by NMR to be at random for the whole range of compositions. The effect exerted by the 5-tert-butyl isophthalate units on thermal, tensile and gas transport properties was evaluated. Both Tm and crystallinity as well as the mechanical moduli were found to decrease steadily with copolymerization whereas Tg increased and the polyesters became more brittle. Permeability and solubility sligthly increased also with the content in substituted units whereas the diffusion coefficient remained practically constant. For the homopolyester poly(5-tert-butyl isophthalate), all these properties were found to deviate significantly from the general trend displayed by copolyesters suggesting that a different chain mode of packing in the amorphous phase is likely adopted in this case
Cutinase: a new tool for biomodification of synthetic fibers

This paper describes two methods to monitor esterase hydrolysis at the surface of polyester fibres (PETPolyethylene terephthalate). The hydroxyl groups were
determined on the fibre surface by alkaline reaction with a reactive dye (CI Reactive Black 5) and colour intensity was determined using a reflectance spectrophotometer.
The terephthalic acid solution formed was also quantified after reaction with peroxide by fluorimetric determination of the resulting hydroxyterephthalic acid.
Detailed descriptions of those methods are given in this paper
Influence of organic solvents on cutinase stability and accessibility to polyamide fibers

ABSTRACT: The stability of cutinase was measured in the presence of imethylacetamide
(DMA) and benzyl alcohol (BA). These solvents are known swelling agents of
polyamide ﬁbers. We found that cutinase retains some stability (half-life of 14 h),
enough for an enzymatic treatment with a solvent composition of 1.5% DMA þ 10%
BA. Enzymatic treatment in the presence of these solvent compositions yields more
soluble amino groups as well as more amino end groups at the ﬁber level. We have
shown evidence that the presence of minor quantities of solvent can increase the
accessibility of the enzyme towards the polyamide ﬁber
Controlled Trans-stereospecific Polymerisation of Isoprene with Neodymium (III) Borohydride-dialkylmagnesium system

International audienceNeodymium trisborohydride, associated with MgR2 alkylating agents, affords an efficient initiator for the stereospecific polymerization of isoprene. This system presents good activity (150 kg of polyisoprene/mol of Nd/h; 95% yield in 2 h) and is trans-stereospecific (up to 97.7%), and its polymerization shows a quasi-living character. The molecular weights are controlled by the [Isoprene]/[Nd] ratio, with a polydispersity index lower than 1.6. A full study is presented here, including the influence of the nature of the alkylating reagent (MgR2), the solvent, the reaction temperature, the [MgR2]/[Nd] ratio, and the replacement of neodymium by other lanthanides. This work also includes a kinetic study of the system and a detailed NMR study of the microstructure of the trans-polyisoprene obtained, providing mechanistic insights about the polymerization reaction
Free Radical Copolymerization of 2,2,2-Trifluoroethyl a-Fluoroacrylate and tert-Butyl a-Trifluoromethylacrylate: Thermal and Optical Properties of the Copolymers

International audienceThe radical copolymerization of 2,2,2-trifluoroethyl a-fluoroacrylate (FATRIFE) with tert-butyl a-trifluoromethylacrylate (MAF-TBE) initiated by tertbutyl 2,2-dimethylperoxypropanoate was investigated in acetonitrile solution. A series of poly(FATRIFE-co-MAF-TBE) copolymers were synthesized with MAF-TBE compositions, determined by 19F NMR, ranging from 12 to 44 mol %. MAF-TBE incorporation was less than 50 mol % as this monomer underwent no radical homopolymerization. The obtained copolymers exhibited number-average molecular weights and polydispersity indexes ranging from 1.5 3 104 to 9.6 3 104 g/mol and from 1.5 to 3.1, respectively. The reactivity ratios were determined by the Kelen-Tu¨ dos method (rFATRIFE ¼ 1.71 6 0.01 and rMAF-TBE ¼ 0 at 74 8C) leading to random copolymers and alternating copolymers when the MAF-TBE molar ratio in copolymer is close to 50 mol %. Thermal and optical properties of the resulting polymers were examined. Glass transition temperatures of copolymers were varying from 89 to 108 8C. Modifying the compositions of these copolymers allowed a precise control over the refractive index measured at 633, 1320, and 1550 n
Synthesis of 4-arm star poly(L-Lactide) oligomers using an in situ-generated calcium-based initiator

Using an in situ-generated calcium-based initiating species derived from pentaerythritol, the bulk synthesis of well-defined 4-arm star poly(L-lactide) oligomers has been studied in detail. The substitution of the traditional initiator, stannous octoate with calcium hydride allowed the synthesis of oligomers that had both low PDIs and a comparable number of polymeric arms (3.7 – 3.9) to oligomers of similar molecular weight. Investigations into the degree of control observed during the course of the polymerization found that the insolubility of pentaerythritol in molten L-lactide resulted in an uncontrolled polymerization only when the feed mole ratio of L-lactide to pentaerythritol was 13. At feed ratios of 40 and greater, a pseudo-living polymerization was observed. As part of this study, in situ FT-Raman spectroscopy was demonstrated to be a suitable method to monitor the kinetics of the ring-opening polymerization (ROP) of lactide. The advantages of using this technique rather than FT-IR-ATR and 1H NMR for monitoring L-lactide consumption during polymerization are discussed
Photoluminescent Energy Transfer from Poly(phenyleneethynylene)s to Near-Infrared Emitting Fluorophores

Photoluminescent energy transfer was investigated in conjugated polymer-fluorophore blended thin films. A pentiptycene-containing poly(phenyleneethynylene) was used as the energy donor, and 13 fluorophores were used as energy acceptors. The efficiency of energy transfer was measured by monitoring both the quenching of the polymer emission and the enhancement of the fluorophore emission. Near-infrared emitting squaraines and terrylenes were identified as excellent energy acceptors. These results, where a new fluorescent signal occurs in the near-infrared region on a completely dark background, offer substantial possibilities for designing highly sensitive turn-on sensors.National Institute of General Medical Sciences (U.S.) (F32GM086044)Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (DAAD-19-02-0002
Catalytic cyclopropanation of polybutadienes

Catalytic cyclopropanation of commercial 1,2- or 1,4-
cis
-polybutadiene, respectively, with ethyl diazoacetate catalyzed
by [Tp
Br3
Cu(NCMe)] (Tp
Br3
¼
hydrotris(3,4,5-tribromo-1-pyrazo-
lyl)borate) at room temperature afforded high molecular weight
(
M
n
>
10
5
mol
 
1
) side-chain or main-chain, respectively, carbox-
yethyl cyclopropyl-substituted polymers with variable and con-
trolled degrees of functionalization. Complete functionalization
of 1,4-
cis
-polybutadiene afforded poly[ethylene-alt-(3-ethoxycar-
bonyl-cyclopropene)]. Catalytic hydrogenation of residual dou-
ble bonds of partially cyclopropanated polybutadienes provided
access to the corresponding saturated polyolefins. Thermal
properties are reported.MICINN CTQ2008-00042BQU MICINN HA2004-0067 Junta de Andalucia P05-FQM091
Oxidation of sec-alcohols with Ru(II)-bearing microgel star polymer catalysts via hydrogen transfer reaction: Unique microgel-core catalysis

Oxidation of sec-alcohols was investigated with ruthenium-bearing microgel core star polymer catalysts [Ru(II)-Star]. The star polymer catalysts were directly prepared via RuCl2(PPh3)3-catalyzed living radical polymerization of methyl methacrylate (MMA), followed by the arm-linking reaction with ethylene glycol dimethacrylate (1) in the presence of diphenylphosphinostyrene (2). The Ru(II)-Star efficiently and homogeneously catalyzed the oxidation of 1-phenylethanol (S1) to give a corresponding ketone (acetophenone) in higher yield (92%) than the analogs of polymer-supported ruthenium complexes. Importantly, the star catalyst afforded high recycling efficiency in the oxidation. They held catalytic activity against three times catalysis even though they were recovered under air-exposure, whereas the conventional RuCl2(PPh3)3 lost the activity for same recycling procedure due to the deactivation by oxygen. The stability of the star catalysts during the recycle experiment was confirmed by detailed spectroscopic characterization. The star polymers also catalyzed oxidation for a wide range of sec-alcohols with aromatic and aliphatic groups. The substrate affinity was different from that with RuCl2(PPh3)3, suggesting the unique selectivity caused by the specific structure
In Situ Synthesis of Polymer/Clay Nanocomposites by Type II Photoinitiated Free Radical Polymerization

Cataloged from PDF version of article.A new synthetic route for the preparation of poly(methyl methacrylate)/montmorillonite (PMMA/MMT) nanocomposites was reported. In this method, first 4-(dimethylamino)benzoate group was incorporated into silicate layers of clay by esterification reaction and used to produce PMMA/MMT nanocomposites by in situ Type II photoinitiated free radical polymerization. In situ photopolymerization of methyl methacrylate through into the silicate layers by either visible or UV light irradiation leads to PMMA/MMT nanocomposites. Copyright © 2011 Wiley Periodicals, Inc
Nanostructured Organic-Inorganic Hybrid Films Prepared by the Sol-Gel Method from Self-Assemblies of PS-b-PAPTES-b-PS Triblock Copolymers

International audienceABA-based triblock copolymers of styrene as block ends and gelable 3-acryloxypropyltriethoxysilane (APTES) as the middle block were successfully prepared through nitroxide-medi- ated polymerization (NMP). The copolymers were bulk self- assembled into films and the degree of phase separation between the two blocks was evaluated by differential scanning calorimetry (DSC). Their morphology was examined through small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM), whereas the mechanical properties of the corresponding cross- linked self-assembled nanostructures were characterized by dynamic mechanical analysis (DMA). Acidic treatment of the tri- block copolymers favored the hydrolysis and condensation reactions of the APTES-rich nanophase, and induced a mechanical reinforcement evidenced by the increase of storage modulus val- ues and the shift of the glass transition temperature to higher tem- peratures due to confinement effects. In addition, the lamellar structure of the hybrid films was retained after the removal of the organic part by calcination
Energy Transfer from Fluorene Based Conjugated Polyelectrolytes to Onchain and Self-Assembled Porphyrin Units

A new water soluble fluorene-based polyelectrolyte containing on-chain porphyrin units has been synthesized via Suzuki coupling, for use in optoelectronic devices. The material consist of a random copolymer of poly{1,4-phenylene-[9,9-bis(4-phenoxy butylsulfonate)]fluorene-2,7-diyl} (PBS-PFP) and a 5,15-diphenylporphyrin (DPP). The energy transfer process between the PBS-PFP units and the porphyrin has been investigated through steady state and time-resolved measurements. The copolymer PBS-PFP-DPP displays two different emissions one located in the blue region of the spectra, corresponding to the fluorene part and another in the red due to fluorescent DPP units either formed directly or by exciton transfer. However, relatively inefficient energy transfer from the PFP to the on-chain porphyrin units was observed. We compare this with a system involving an anionic blue light-emitting donor PBS-PFP and a anionic red light-emitting energy acceptor meso-tetrakisphenylporphyrinsulfonate (TPPS), self-assembled by electrostatic attraction induced by Ca2+. Based on previous studies related to chain aggregation of the anionic copolymer PBS-PFP, two different solvent media were chosen to further explore the possibilities of the self-assembled system: dioxane–water and aqueous nonionic surfactant n-dodecylpentaoxyethylene glycol ether (C12E5). In contrast, with the on-chain PBS-PFP-DPP system the strong overlap of the 0-0 emission peak of the PBS-PFP and the Soret absorption band of the TPPS results in an efficient Förster transfer. This is strongly dependent on the solvent medium used
Thermal Frontal Polymerization with a Thermally Released Redox\ud
Catalyst

We studied thermal frontal polymerization using a redox\ud
systemin an attempt to lower the temperature of the frontally\ud
polymerizable system while increasing the front velocity so as to\ud
obtain a self-sustaining front in a thinner layer than without the\ud
redox components. A cobalt-containing polymer with a melting\ud
point of 63  C (Intelimer 6050X11) and cumene hydroperoxide\ud
were used with a triacrylate. The use of the Intelimer decreased\ud
the front velocity but allowed fronts to propagate in thinner layers\ud
and withmore filler while still having a pot life of days. Nonplanar\ud
modes of propagation occurred. Fronts propagated faster when\ud
6-O-palmitoyl-L-ascorbic acid was used as a reductant. Interestingly,\ud
fronts were also faster with the reductant even without the\ud
Intelimer if kaolin clay was the filler; however, the pot life was significantly\ud
reduce
Hyperbranched polymers as delivery vectors for oligonucleotides

We report on the synthesis and characterization of hyperbranched dimethylaminoethyl methacrylate (DMAEMA) polymers using reversible addition fragmentation chain transfer polymerization. These polymers are unimolecular and globular and hence interact differently with DNA than conventional DMAEMA or block copolymers. The polymers were shown to effectively bind and condense oligonucleotides (ODNs); visualization of the bound complexes was achieved using atomic force microscopy, whereas isothermal titration calorimetry described the thermodynamics of binding. The ODNs were effectively protected from enzymatic degradation (DNAses) when condensed by all the polycations studied. However, internalization of the complexes into HeLa cells was less effective when the polycation was chain extended with polyethyleneglycol monomethylether methacrylate. Conjugation of folic acid to the periphery of the polycation facilitated much enhanced uptake of the oligomeric DNA into the HeLa cells due to overexpression of folate receptors on the surface of HeLa cells. Although significant cytotoxicity was observed at high polymer concentrations, this could be alleviated by shielding of the polycation using poly(ethyleneglycol monomethylether methacrylate). These results suggest that hyperbranched polymers formed in this way exhibit interesting complexation behavior with ODNs and thus are promising models to study as gene delivery vectors.Full Tex
Optical and Electronic Properties of Fluorene-Based Copolymers and Their Sensory Applications

Cataloged from PDF version of article.A series of novel, fluorene-based conjugated copolymers, poly[(9,9-bis{propenyl}-9H-fluorene)-co-(9,9-dihexyl-9H-fluorene)] (P1), poly[(9,9-bis{carboxymethylsulfonyl-propyl}-fluorenyl-2,7-diyl)-co-(9,9-dihexyl-9H-fluorene)] (P2) and poly[(9,9-dihexylfluorene)-co-alt-(9,9-bis-(6-azidohexyl)fluorene)] (P3), are synthesized by Suzuki coupling reactions and their electrochemical properties, in the form of films, are investigated using cyclic voltammetry. The results reveal that the polymer films exhibit electrochromic properties with a pseudo-reversible redox behavior; transparent in the neutral state and dark violet in the oxidized state. Among the three polymers, P2 possesses the shortest response time and the highest coloration efficiency value. These polymers emit blue light with a band gap value of around 2.9 eV and have high fluorescent quantum yields. Their metal ion sensory abilities are also investigated by titrating them with a number of different transition metal ions; all of these polymers exhibit a higher selectivity toward Fe3+ ions than the other ions tested with Stern-Volmer constants of 4.41 x 10(6) M-1, 3.28 x 10(7) M-1, 1.25 x 10(6) M-1, and 6.56 x 10(6) M-1 for P1, P2, water soluble version of P2 (P2S) and P3, respectively. (C) 2012 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 815-82
Three-dimensional microfabrication of protein hydrogels via two-photon-excited thiol-vinyl ester photopolymerization

Engineering three-dimensional (3D) hydrogels with well-defined architectures has become increasingly important for tissue engineering and basic research in biomaterials science. To fabricate 3D hydrogels with (sub)cellular-scale features, two-photon polymerization (2PP) shows great promise although the technique is limited by the selection of appropriate hydrogel precursors. In this study, we report the synthesis of gelatin hydrolysate vinyl esters (GH-VE) and its copolymerization with reduced derivatives of bovine serum albumin (acting as macrothiols). Photorheology of the thiol-ene copolymerization shows a much more rapid onset of polymerization and a higher end modulus in reference to neat GH-VE. This allowed 2PP to provide well-defined and stable hydrogel microstructures. Efficiency of the radical-mediated thiol-vinyl ester photopolymerization allows high 2PP writing speed (as high as 50 mm s−1) with low laser power (as low as 20 mW). MTT assays indicate negligible cytotoxicities of the GH-VE macromers and of the thiol-ene hydrogel pellets. Osteosarcoma cells seeded onto GH-VE/BSA hydrogels with different macromer relative ratios showed a preference for hydrogels with higher percentage of GH-VE. This can be attributed both to a favorable modulus and preferable protein environment since gelatin favors cell adhesion and albumin incurs nonspecific binding
FT-IR characterization and hydrolysis of PLA-PEG-PLA based copolyester hydrogels with short PLA segments and a cytocompatibility study

A series of the biodegradable copolyester hydrogels was prepared using a redox-initiated polymerization with a constant 1:9 mole ratio of the Boltorn-based acrylate and diacrylate triblock comacromonomers. The Boltorn (R) macromonomer was derived from the hyperbranched polyester Boltorn H20, which was functionalized at each terminus with poly(ethylene glycol) acrylate, and the diacrylate triblock macromonomer was poly (lactide-b-ethylene glycol-b-lactide) diacrylate. The hydrolysis of the copolyesters at pH 7.4 in a phosphate buffered saline solution at 37 degrees C was studied using ATR-FTIR spectroscopy. It was found that the presence of the Boltorn, the PEG, and lactide block lengths both play vital roles in determining the structure-property relationships in these materials. The ATR-FTIR studies showed that with increasing lactide segment length, the rate of ester hydrolysis increased due to the increased concentration of the hydrolytically sensitive poly(lactic acid) (PLA) ester groups in the network. However, incorporation of Boltorn into the PLA-PEG-PLA copolymer did not significantly change the kinetic rate constant for hydrolysis of the PLA segments. The cytocompatibility of a typical one of these materials in the presence of its degradation by-products was assessed using cultured osteoblasts from the rat. The hydrogel was degraded for 28 days and found to be cytocompatible with osteoblasts over days 23 to 28 of the hydrolysis period. (c) 2013 Wiley Periodicals, Inc