Read by QxMD icon Read


Justin P Cole, Celia R Federico, Chern-Hooi Lim, Garret M Miyake
Photoinduced organocatalyzed atom-transfer radical polymerization (O-ATRP) is a controlled radical polymerization methodology that can be mediated by organic photoredox catalysts under the influence of light. However, typical O-ATRP systems require relatively high catalyst loadings (1000 ppm) to achieve control over the polymerization. Here, new core-extended diaryl dihydrophenazine photoredox catalysts were developed for O-ATRP and demonstrated to efficiently operate at low catalyst loadings of 5-50 ppm to produce polymers with excellent molecular weight control and low dispersity, while achieving near-quantitative initiator efficiency...
January 22, 2019: Macromolecules
Ivan Terzic, Niels L Meereboer, Mónica Acuautla, Giuseppe Portale, Katja Loos
A facile ferroelectric nanostructures preparation method is developed based on the self-assembly of poly(2-vinylpyridine)- b -poly(vinylidene fluoride- co -trifluoroethylene)- b -poly(2-vinylpyridine) triblock copolymers (P2VP- b -P(VDF-TrFE)- b -P2VP), and the effect of morphological characteristics of the block copolymers on the ferroelectric response has been investigated for the first time. By simple adjustment of the ratio between the blocks, lamellar, cylindrical, and spherical morphologies are obtained in the melt and preserved upon crystallization of P(VDF-TrFE)...
January 8, 2019: Macromolecules
Fabian Muralter, Alberto Perrotta, Anna Maria Coclite
In this contribution, the temperature-dependent swelling behavior of vapor-deposited smart polymer thin films is shown to depend on cross-linking and deposited film thickness. Smart polymers find application in sensor and actuator setups and are mostly fabricated on delicate substrates with complex nanostructures that need to be conformally coated. As initiated chemical vapor deposition (iCVD) meets these specific requirements, the present work concentrates on temperature-dependent swelling behavior of iCVD poly( N -isopropylacrylamide) thin films...
December 11, 2018: Macromolecules
Arijana Susa, Anton Mordvinkin, Kay Saalwächter, Sybrand van der Zwaag, Santiago J Garcia
We present a systematic study of the role of the aromatic dianhydride structure on the self-healing behavior of dimer diamine-based polyimides. By means of solid-state NMR and rheology, we studied the molecular and microscale dynamics of four polyimides comprising the same aliphatic branched diamine yet with variable dianhydride rigidities and correlated these to their macroscopic healing kinetics measured by tensile testing. Following the two-step kinetics of the healing process, we were able to differentiate and quantify the extent of mechanical strength recovery in each of the healing stages separately...
November 13, 2018: Macromolecules
Gijs M Ter Huurne, Ilja K Voets, Anja R A Palmans, E W Meijer
Anfinsen's famous experiment showed that the restoration of catalytic activity of a completely unfolded ribonuclease A is only possible when the correct order of events is followed during the refolding process. Inspired by this work, the effect of structural constraints induced by covalent cross-links on the folding of a synthetic polymer chain via hydrogen-bonding interactions is investigated. Hereto, methacrylate-based monomers comprising either benzene-1,3,5-tricarboxamide (BTA)-based or coumarin-based pendants are copolymerized with n -butyl methacrylate in various ratios via reversible addition-fragmentation chain-transfer (RAFT) polymerization...
November 13, 2018: Macromolecules
Nicholas J Warren, Matthew J Derry, Oleksandr O Mykhaylyk, Joseph R Lovett, Liam P D Ratcliffe, Vincent Ladmiral, Adam Blanazs, Lee A Fielding, Steven P Armes
Reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 2-hydroxypropyl methacrylate was used to prepare three poly(glycerol monomethacrylate) x -poly(2-hydroxypropyl methacrylate) y (denoted G x -H y  or PGMA-PHPMA) diblock copolymers, namely G37 -H80 , G54 -H140 , and G71 -H200 . A master phase diagram was used to select each copolymer composition to ensure that a pure worm phase was obtained in each case, as confirmed by transmission electron microscopy (TEM) and small-angle x-ray scattering (SAXS) studies...
November 13, 2018: Macromolecules
Piotr Batys, Yanpu Zhang, Jodie L Lutkenhaus, Maria Sammalkorpi
The combination of all-atom molecular dynamics simulations with differential scanning calorimetry (DSC) has been exploited to investigate the influence of temperature and hydration on the water distribution and mobility in poly(diallyldimethylammonium) (PDADMA) and poly(sodium 4-styrenesulfonate) (PSS) complexes. The findings show that the vast majority of the water molecules hydrating the polyelectrolyte complexes (PECs) with 18-30 wt % hydration are effectively immobilized due to the strong interactions between the PE charge groups and water...
October 23, 2018: Macromolecules
Alexei D Filippov, Ilse A van Hees, Remco Fokkink, Ilja K Voets, Marleen Kamperman
The synthesis of charged polymers often requires the polymerization of protected monomers, followed by a polymer-analogous reaction to the polyelectrolyte product. We present a mild, facile method to cleave tert -butyl groups from poly( tert -butyl acrylate) blocks that yields poly(acrylic acid) (pAA) blocks free of traces of the ester. The reaction utilizes a slight excess of HCl in hexafluoroisopropanol (HFIP) at room temperature and runs to completion within 4 h. We compare deprotection in HFIP with the common TFA/DCM method and show that the latter does not yield clean pAA...
October 23, 2018: Macromolecules
O J Deane, J R Lovett, O M Musa, A Fernyhough, S P Armes
Poly( N -vinylpyrrolidone) (PNVP) is a well-known, highly polar, nonionic water-soluble polymer. However, N -vinylpyrrolidone (NVP) usually exhibits strongly non-ideal behavior when copolymerized with methacrylic or styrenic monomers. Moreover, NVP is not particularly well-controlled under living radical polymerization conditions. For these reasons, alternative pyrrolidone-based monomers have been investigated. For example, the reversible addition-fragmentation chain transfer (RAFT) polymerization of 2-( N -methacryloyloxy)ethylpyrrolidone (NMEP) has been recently investigated using various polymerization formulations...
October 9, 2018: Macromolecules
Dorette S Tromp, Marianne Lankelma, Hannah de Valk, Emile de Josselin de Jong, Bas de Bruin
Herein we describe the Rh-catalyzed C1 polymerization of silyl-protected diazoacetates of the general formula HC(=N2 )C(=O)O(CH2 ) x OSiR3 , where x = 2-5. After polymerization and subsequent desilylation, syndiotactic polymers bearing a hydroxy-containing side group on every backbone carbon are obtained. The molecular weight of the desired polymers can be controlled via chain transfer with methanol during the polymerization. The produced polymers are compared to atactic analogues formed by [(η3 -C3 H5 )PdCl]-catalyzed polymerization of silyl-protected diazoacetates with the same general formula...
September 25, 2018: Macromolecules
Lambert Baij, Joen J Hermans, Katrien Keune, Piet D Iedema
In the restoration of paintings, solvent diffusion and swelling of polymeric oil paint binding media are important factors to consider. Common cleaning methods with organic solvents or aqueous solutions could lead to undesirable physicochemical changes in the paint in the long term, though the extent of this effect is not yet clear. We used tailored nonporous model systems for aged oil paint to measure paint swelling and solvent diffusion for a wide range of relevant solvents. Using dynamic mechanical analysis (DMA), the glass transition temperature of our model systems was found to be close to room temperature...
September 25, 2018: Macromolecules
Zhenyu J Zhang, Steve Edmondson, Matthew Mears, Jeppe Madsen, Steven P Armes, Graham J Leggett, Mark Geoghegan
The diffusion of rhodamine-labeled poly(ethylene glycol) (r-PEG) within surface-grafted poly(ethylene glycol) (s-PEG) layers in aqueous solution at 18 °C was measured by fluorescence correlation spectroscopy. The diffusion coefficient of r-PEG within s-PEG was controlled by the grafting density, σ, and scaled as σ-1.42±0.09 . It is proposed that a characteristic blob size associated with the grafted (brush) layer defines the region through which the r-PEG diffusion occurs. The diffusion coefficients for r-PEG in semidilute solution were found to be similar to those in the brushes...
August 28, 2018: Macromolecules
Juan Wang, Remy C Cooper, Hongliang He, Boxuan Li, Hu Yang
In this paper, we report on the fabrication of micron-sized dendrimer hydrogels (μDHs) using the water-in-oil (w/o) inverse microemulsion method coupled with the highly efficient aza -Michael addition. EDA core polyamidoamine (PAMAM) dendrimer G5 (10 w%) and polyethylene glycol diacrylate (PEG-DA, M n = 575 g/mol) (the molar ratio of amine/acrylate = 1/1) were dissolved in the water phase and added to hexane in the presence of surfactants span 80/tween 80 (5/1, w/w) (volume ratio of hexane to surfactants: 70:1) to form w/o microemulsions, in which PAMAM G5 cross-links with PEG-DA via the aza -Michael addition reaction...
August 14, 2018: Macromolecules
Kai Zhang, Aaditya Suratkar, Sitara Vedaraman, Vasudevan Lakshminarayanan, Laurence Jennings, Piotr J Glazer, Jan H van Esch, Eduardo Mendes
While the formation of (tri)block copolymer hydrogels has been extensively investigated, such studies mostly focused on equilibrium self-assembling whereas the use of preformed structures as building blocks such as out of equilibrium, quenched, nanofibrillar micelles is still a challenge. Here, we demonstrate that quenched, ultralong polystyrene- b -poly(ethylene oxide) (PS- b -PEO) micelles can be used as robust precursors of hydrogels. Two cross-linking strategies, (i) thermal fusion of micellar cores and (ii) chemical cross-linking of preformed micellar coronas were studied...
August 14, 2018: Macromolecules
Chidambar Kulkarni, Stefan C J Meskers, Anja R A Palmans, E W Meijer
Chiral conjugated polymers bearing enantiopure side chains offer the possibility to harness the effect of chirality in organic electronic devices. However, its use is hampered by the low degree of circular polarization in absorption ( g abs ) in most of the conjugated polymer thin-films studied. Here we demonstrate a versatile method to significantly increase the g abs by using a few weight percentages of a commercially available achiral long-chain alcohol as an additive. This additive enhances the chiroptical properties in both absorption and emission by ca...
August 14, 2018: Macromolecules
Alberto Perrotta, Paul Christian, Andrew O F Jones, Fabian Muralter, Anna Maria Coclite
Control over thin film growth (e.g., crystallographic orientation and morphology) is of high technological interest as it affects several physicochemical material properties, such as chemical affinity, mechanical stability, and surface morphology. The effect of process parameters on the molecular organization of perfluorinated polymers deposited via initiated chemical vapor deposition (iCVD) has been previously reported. We showed that the tendency of poly(1 H ,1 H ,2 H ,2 H -perfluorodecyl acrylate) (pPFDA) to organize in an ordered lamellar structure is a function of the filament and substrate temperatures adopted during the iCVD process...
August 14, 2018: Macromolecules
Willem E M Noteborn, Joeri A J Wondergem, Anastasiia Iurchenko, Farhad Chariyev-Prinz, Dominique Donato, Ilja K Voets, Doris Heinrich, Roxanne E Kieltyka
Nucleic acid-polymer conjugates are an attractive class of materials endowed with tunable and responsive character. Herein, we exploit the dynamic character of nucleic acids in the preparation of hybrid DNA-covalent polymers with extendable grafts by the hybridization chain reaction. Addition of DNA hairpins to an initiator DNA-dextran graft copolymer resulted in the growth of the DNA grafts as evidenced by various characterization techniques over several length scales. Additionally, aggregation of the initiator DNA-graft copolymer before the hybridization chain reaction was observed resulting in the formation of kinetically trapped aggregates several hundreds of nanometers in diameter that could be disrupted by a preheating step at 60 °C prior to extension at room temperature...
July 24, 2018: Macromolecules
Tuukka Verho, Antti Paajanen, Jukka Vaari, Anssi Laukkanen
We carried out large-scale atomistic molecular dynamics simulations to study the growth of twin lamellar crystals of polyethylene initiated by small crystal seeds. By examining the size distribution of the stems-straight crystalline polymer segments-we show that the crystal edge has a parabolic profile. At the growth front, there is a layer of stems too short to be stable, and new stable stems are formed within this layer, leading to crystal growth. Away from the edge, the lengthening of the stems is limited by a lack of available slack length in the chains...
July 10, 2018: Macromolecules
Milad Golkaram, Csaba Fodor, Evelyne van Ruymbeke, Katja Loos
Supramolecular polymers bearing weak hydrogen bonds (sticker) can express outstanding dynamic properties due to their labile association. Studying the linear viscoelasticity (LVE) of this type of polymer can provide us with sufficient knowledge to design polymeric materials for applications that need dynamic properties such as self-healing. Using different compositions of flexible weak stickers, LVE analysis showed scalings corresponding to a transition from a linear precursor to a cluster. By introducing one sticker per repeating unit of the precursor polymer, the effect of sticker distribution along the chain as well as phase separation is excluded...
July 10, 2018: Macromolecules
Carolus H R M Wilsens, Laurence G D Hawke, Enrico M Troisi, Daniel Hermida-Merino, Gijs de Kort, Nils Leoné, Ketie Saralidze, Gerrit W M Peters, Sanjay Rastogi
We report on the effect of an aliphatic oxalamide based nucleating agent ( OXA3,6 ) on the melt and crystallization behavior of isotactic polypropylene ( i PP) under defined shear conditions. Through polarized optical microscopy, we demonstrate that OXA3,6 self-assembles from the i PP melt into rhombic crystals whereas their size and distribution proved highly dependent on the employed cooling rates. The presence of 0.5 wt % of OXA3,6 in i PP results in a significant suppression in i PP melt viscosity, which could not be explained via molecular modeling...
July 10, 2018: Macromolecules
Fetch more papers »
Fetching more papers... Fetching...
Read by QxMD. Sign in or create an account to discover new knowledge that matter to you.
Remove bar
Read by QxMD icon Read

Search Tips

Use Boolean operators: AND/OR

diabetic AND foot
diabetes OR diabetic

Exclude a word using the 'minus' sign

Virchow -triad

Use Parentheses

water AND (cup OR glass)

Add an asterisk (*) at end of a word to include word stems

Neuro* will search for Neurology, Neuroscientist, Neurological, and so on

Use quotes to search for an exact phrase

"primary prevention of cancer"
(heart or cardiac or cardio*) AND arrest -"American Heart Association"