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Macromolecules

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https://www.readbyqxmd.com/read/29805184/synthesis-of-high-molecular-weight-poly-glycerol-monomethacrylate-via-raft-emulsion-polymerization-of-isopropylideneglycerol-methacrylate
#1
Craig P Jesson, Victoria J Cunningham, Mark J Smallridge, Steven P Armes
High molecular weight water-soluble polymers are widely used as flocculants or thickeners. However, synthesis of such polymers via solution polymerization invariably results in highly viscous fluids, which makes subsequent processing somewhat problematic. Alternatively, such polymers can be prepared as colloidal dispersions; in principle, this is advantageous because the particulate nature of the polymer chains ensures a much lower fluid viscosity. Herein we exemplify the latter approach by reporting the convenient one-pot synthesis of high molecular weight poly(glycerol monomethacrylate) (PGMA) via the reversible addition-fragmentation chain transfer (RAFT) aqueous emulsion polymerization of a water-immiscible protected monomer precursor, isopropylideneglycerol methacrylate (IPGMA) at 70 °C, using a water-soluble poly(glycerol monomethacrylate) (PGMA) chain transfer agent as a steric stabilizer...
May 8, 2018: Macromolecules
https://www.readbyqxmd.com/read/29910512/physical-networks-from-multifunctional-telechelic-star-polymers-a-rheological-study-by-experiments-and-simulations
#2
Vishal Metri, Ameur Louhichi, Jiajun Yan, Guilhem P Baeza, Krzysztof Matyjaszewski, Dimitris Vlassopoulos, Wim J Briels
The equilibrium mechanical properties of a cross-linked gel of telechelic star polymers are studied by rheology and Brownian dynamics simulations. The Brownian dynamics model consists of cores to which Rouse arms are attached. Forces between the cores are obtained from a potential of mean force model developed by Likos and co-workers. Both experimentally and in the simulations, networks were created by attaching sticker groups to the ends of the arms of the polymers, which were next allowed to form bonds among them in a one to one fashion...
April 24, 2018: Macromolecules
https://www.readbyqxmd.com/read/29657338/size-dependent-submerging-of-nanoparticles-in-polymer-melts-effect-of-line-tension
#3
Shanqiu Liu, Anupam Pandey, Joost Duvigneau, Julius Vancso, Jacco H Snoeijer
Adhesion of nanoparticles to polymer films plays a key role in various polymer technologies. Here we report experiments that reveal how silica nanoparticles adhere to a viscoelastic PMMA film above the glass transition temperature. The polymer was swollen with CO2 , closely matching the conditions of nanoparticle-nucleated polymer foaming. It is found that the degree by which the particles sink into the viscoelastic substrate is strongly size dependent and can even lead to complete engulfment for particles of diameter below 12 nm...
April 10, 2018: Macromolecules
https://www.readbyqxmd.com/read/29681653/photonic-resins-designing-optical-appearance-via-block-copolymer-self-assembly
#4
Dong-Po Song, Gianni Jacucci, Feyza Dundar, Aditi Naik, Hua-Feng Fei, Silvia Vignolini, James J Watkins
Despite a huge variety of methodologies having been proposed to produce photonic structures by self-assembly, the lack of an effective fabrication approach has hindered their practical uses. These approaches are typically limited by the poor control in both optical and mechanical properties. Here we report photonic thermosetting polymeric resins obtained through brush block copolymer (BBCP) self-assembly. We demonstrate that the control of the interplay between order and disorder in the obtained photonic structure offers a powerful tool box for designing the optical appearance of the polymer resins in terms of reflected wavelength and scattering properties...
March 27, 2018: Macromolecules
https://www.readbyqxmd.com/read/29599567/evaluation-of-blob-theory-for-the-diffusion-of-dna-in-nanochannels
#5
Damini Gupta, Aditya Bikram Bhandari, Kevin D Dorfman
We have measured the diffusivity of λ-DNA molecules in approximately square nanochannels with effective sizes ranging from 117 nm to 260 nm at moderate ionic strength. The experimental results do not agree with the non-draining scaling predicted by blob theory. Rather, the data are consistent with the predictions of previous simulations of the Kirkwood diffusivity of a discrete wormlike chain model, without the need for any fitting parameters.
March 13, 2018: Macromolecules
https://www.readbyqxmd.com/read/29479117/odijk-excluded-volume-interactions-during-the-unfolding-of-dna-confined-in-a-nanochannel
#6
Jeffrey G Reifenberger, Han Cao, Kevin D Dorfman
We report experimental data on the unfolding of human and E. coli genomic DNA molecules shortly after injection into a 45 nm nanochannel. The unfolding dynamics are deterministic, consistent with previous experiments and modeling in larger channels, and do not depend on the biological origin of the DNA. The measured entropic unfolding force per friction per unit contour length agrees with that predicted by combining the Odijk excluded volume with numerical calculations of the Kirkwood diffusivity of confined DNA...
February 13, 2018: Macromolecules
https://www.readbyqxmd.com/read/29472729/behavior-of-weak-polyelectrolyte-brushes-in-mixed-salt-solutions
#7
Joshua D Willott, Timothy J Murdoch, Frans A M Leermakers, Wiebe M de Vos
Hydrophilic and hydrophobic weak polybasic brushes immersed in aqueous solutions of mixed salt counterions are considered using a mean-field numerical self-consistent field approach. On top of the solvent quality of the polymer, the counterion-solvent interactions are accounted for by implementing Flory-Huggins interaction parameters. We show that ion specificity within the brush can bring about large changes in conformation. It is found that the collapse transition of hydrophobic, weak polyelectrolyte brushes features an intermediate two-phase state wherein a subset of chains are collapsed in a dense layer at the substrate, while the remainder of chains are well-solvated and strongly stretched away from the it...
February 13, 2018: Macromolecules
https://www.readbyqxmd.com/read/29910511/the-multifaceted-role-of-methylaluminoxane-in-metallocene-based-olefin-polymerization-catalysis
#8
Marjolein E Z Velthoen, Ara Muñoz-Murillo, Abdelkbir Bouhmadi, Michaël Cecius, Steve Diefenbach, Bert M Weckhuysen
In single-site olefin polymerization catalysis, a large excess of cocatalyst is often required for the generation of highly active catalysts, but the reason for this is unclear. In this work, fundamental insight into the multifaceted role of cocatalyst methylaluminoxane (MAO) in the activation, deactivation, and stabilization of group 4 metallocenes in the immobilized single-site olefin polymerization catalyst was gained. Employing probe molecule FT-IR spectroscopy, it was found that weak Lewis acid sites, inherent to the silica-supported MAO cocatalyst, are the main responsible species for the genesis of active metallocenes for olefin polymerization...
January 23, 2018: Macromolecules
https://www.readbyqxmd.com/read/29706666/characterizing-the-interface-scaling-of-high-%C3%AF-block-copolymers-near-the-order-disorder-transition
#9
Daniel F Sunday, Michael J Maher, Adam F Hannon, Christopher D Liman, Summer Tein, Gregory Blachut, Yusuke Asano, Christopher J Ellison, C Grant Willson, R Joseph Kline
Advancements in the directed self-assembly of block copolymers (BCPs) have prompted the development of new materials with larger effective interaction parameters ( χ e ). This enables BCP systems with phase separation at increasingly small degrees of polymerization ( N ). Very often these systems reside near the order-disorder transition and fit between the weak and strong segregation limits where the behavior of BCP systems is not as thoroughly understood. Utilizing resonant soft X-ray reflectivity (RSoXR) enables both the BCP pitch ( L 0 ) and interface width ( w M ) to be determined simultaneously, through a direct characterization of the composition profile of BCP lamellae oriented parallel to a substrate...
January 9, 2018: Macromolecules
https://www.readbyqxmd.com/read/29339838/force-and-scale-dependence-of-the-elasticity-of-self-assembled-dna-bottle-brushes
#10
Márcio Santos Rocha, Ingeborg M Storm, Raniella Falchetto Bazoni, Ésio Bessa Ramos, Armando Hernandez-Garcia, Martien A Cohen Stuart, Frans Leermakers, Renko de Vries
As a model system to study the elasticity of bottle-brush polymers, we here introduce self-assembled DNA bottle brushes, consisting of a DNA main chain that can be very long and still of precisely defined length, and precisely monodisperse polypeptide side chains that are physically bound to the DNA main chains. Polypeptide side chains have a diblock architecture, where one block is a small archaeal nucleoid protein Sso7d that strongly binds to DNA. The other block is a net neutral, hydrophilic random coil polypeptide with a length of exactly 798 amino acids...
January 9, 2018: Macromolecules
https://www.readbyqxmd.com/read/29296030/self-consistent-field-lattice-model-for-polymer-networks
#11
Nicholas B Tito, Cornelis Storm, Wouter G Ellenbroek
A lattice model based on polymer self-consistent field theory is developed to predict the equilibrium statistics of arbitrary polymer networks. For a given network topology, our approach uses moment propagators on a lattice to self-consistently construct the ensemble of polymer conformations and cross-link spatial probability distributions. Remarkably, the calculation can be performed "in the dark", without any prior knowledge on preferred chain conformations or cross-link positions. Numerical results from the model for a test network exhibit close agreement with molecular dynamics simulations, including when the network is strongly sheared...
December 26, 2017: Macromolecules
https://www.readbyqxmd.com/read/29296029/-50th-anniversary-perspective-a-perspective-on-polyelectrolyte-solutions
#12
REVIEW
M Muthukumar
From the beginning of life with the information-containing polymers until the present era of a plethora of water-based materials in health care industry and biotechnology, polyelectrolytes are ubiquitous with a broad range of structural and functional properties. The main attribute of polyelectrolyte solutions is that all molecules are strongly correlated both topologically and electrostatically in their neutralizing background of charged ions in highly polarizable solvent. These strong correlations and the necessary use of numerous variables in experiments on polyelectrolytes have presented immense challenges toward fundamental understanding of the various behaviors of charged polymeric systems...
December 26, 2017: Macromolecules
https://www.readbyqxmd.com/read/29296028/supernucleation-and-orientation-of-poly-butylene-terephthalate-crystals-in-nanocomposites-containing-highly-reduced-graphene-oxide
#13
Samuele Colonna, Ricardo A Pérez-Camargo, Haiming Chen, Guoming Liu, Dujin Wang, Alejandro J Müller, Guido Saracco, Alberto Fina
The ring-opening polymerization of cyclic butylene terephthalate into poly(butylene terephthalate) (pCBT) in the presence of reduced graphene oxide (RGO) is an effective method for the preparation of polymer nanocomposites. The inclusion of RGO nanoflakes dramatically affects the crystallization of pCBT, shifting crystallization peak temperature to higher temperatures and, overall, increasing the crystallization rate. This was due to a supernucleating effect caused by RGO, which is maximized by highly reduced graphene oxide...
December 12, 2017: Macromolecules
https://www.readbyqxmd.com/read/29213150/strategies-to-increase-the-thermal-stability-of-truly-biomimetic-hydrogels-combining-hydrophobicity-and-directed-hydrogen-bonding
#14
Hongbo Yuan, Jialiang Xu, Eliane P van Dam, Giulia Giubertoni, Yves L A Rezus, Roel Hammink, Huib J Bakker, Yong Zhan, Alan E Rowan, Chengfen Xing, Paul H J Kouwer
Enhancing the thermal stability of proteins is an important task for protein engineering. There are several ways to increase the thermal stability of proteins in biology, such as greater hydrophobic interactions, increased helical content, decreased occurrence of thermolabile residues, or stable hydrogen bonds. Here, we describe a well-defined polymer based on β-helical polyisocyanotripeptides (TriPIC) that uses biological approaches, including hydrogen bonding and hydrophobic interactions for its exceptional thermal stability in aqueous solutions...
November 28, 2017: Macromolecules
https://www.readbyqxmd.com/read/29213149/effect-of-rubber-polarity-on-cluster-formation-in-rubbers-cross-linked-with-diels-alder-chemistry
#15
L M Polgar, E Hagting, P Raffa, M Mauri, R Simonutti, F Picchioni, M van Duin
Diels-Alder chemistry has been used for the thermoreversible cross-linking of furan-functionalized ethylene/propylene (EPM) and ethylene/vinyl acetate (EVM) rubbers. Both furan-functionalized elastomers were successfully cross-linked with bismaleimide to yield products with a similar cross-link density. NMR relaxometry and SAXS measurements both show that the apolar EPM- g -furan precursor contains phase-separated polar clusters and that cross-linking with polar bismaleimide occurs in these clusters. The heterogeneously cross-linked network of EPM- g -furan contrasts with the homogeneous network in the polar EVM- g -furan...
November 28, 2017: Macromolecules
https://www.readbyqxmd.com/read/29755139/thermomechanical-properties-and-glass-dynamics-of-polymer-tethered-colloidal-particles-and-films
#16
Yu Cang, Anna N Reuss, Jaejun Lee, Jiajun Yan, Jianan Zhang, Elena Alonso-Redondo, Rebecca Sainidou, Pascal Rembert, Krzysztof Matyjaszewski, Michael R Bockstaller, George Fytas
Polymer-tethered colloidal particles (aka "particle brush materials") have attracted interest as a platform for innovative material technologies and as a model system to elucidate glass formation in complex structured media. In this contribution, Brillouin light scattering is used to sequentially evaluate the role of brush architecture on the dynamical properties of brush particles in both the individual and assembled (film) state. In the former state, the analysis reveals that brush-brush interactions as well as global chain relaxation sensitively depend on grafting density; i...
November 14, 2017: Macromolecules
https://www.readbyqxmd.com/read/29503464/buckling-instabilities-in-polymer-brush-surfaces-via-postpolymerization-modification
#17
Wei Guo, Cassandra M Reese, Li Xiong, Phillip K Logan, Brittany J Thompson, Christopher M Stafford, Anton V Ievlev, Bradley S Lokitz, Olga S Ovchinnikova, Derek L Patton
We report a simple route to engineer ultrathin polymer brush surfaces with wrinkled morphologies using post-polymerization modification (PPM), where the length scale of the buckled features can be tuned from hundreds of nanometers to one micrometer using PPM reaction time. We show that partial crosslinking of the outer layer of the polymer brush under poor solvent conditions is critical to obtain wrinkled morphologies upon swelling. Characterization of the PPM kinetics and swelling behavior via ellipsometry and the through-thickness composition profile via time-of-flight secondary ion mass spectroscopy (ToF-SIMS) provided keys insight into parameters influencing the buckling behavior...
November 14, 2017: Macromolecules
https://www.readbyqxmd.com/read/29151620/-in-silico-synthesis-of-microgel-particles
#18
Nicoletta Gnan, Lorenzo Rovigatti, Maxime Bergman, Emanuela Zaccarelli
Microgels are colloidal-scale particles individually made of cross-linked polymer networks that can swell and deswell in response to external stimuli, such as changes to temperature or pH. Despite a large amount of experimental activities on microgels, a proper theoretical description based on individual particle properties is still missing due to the complexity of the particles. To go one step further, here we propose a novel methodology to assemble realistic microgel particles in silico . We exploit the self-assembly of a binary mixture composed of tetravalent (cross-linkers) and bivalent (monomer beads) patchy particles under spherical confinement in order to produce fully bonded networks...
November 14, 2017: Macromolecules
https://www.readbyqxmd.com/read/29151619/improving-the-folding-of-supramolecular-copolymers-by-controlling-the-assembly-pathway-complexity
#19
Gijs M Ter Huurne, Lafayette N J de Windt, Yiliu Liu, E W Meijer, Ilja K Voets, Anja R A Palmans
A family of amphiphilic, heterograft copolymers containing hydrophilic, hydrophobic, and supramolecular units based on Jeffamine M-1000, dodecylamine, and benzene-1,3,5-tricarboxamide (BTA) motifs, respectively, was prepared via a postfunctionalization approach. The folding of the copolymers in water into nanometer-sized particles was analyzed by a combination of dynamic and static light scattering, circular dichroism spectroscopy, and small-angle neutron scattering. The sample preparation protocol was crucial for obtaining reproducible and consistent results, showing that only full control over the structure and pathway complexity will afford the desired folded structure, a phenomenon similar to protein folding...
November 14, 2017: Macromolecules
https://www.readbyqxmd.com/read/29151618/heterofunctional-poly-ethylene-glycol-peg-macroinitiator-enabling-controlled-synthesis-of-abc-triblock-copolymers
#20
Lies A L Fliervoet, Marzieh Najafi, Mathew Hembury, Tina Vermonden
ABC triblock copolymers with a poly(ethylene glycol) (PEG) midblock have attractive properties for biomedical applications because of PEG's favorable properties regarding biocompatibility and hydrophilicity. However, easy strategies to synthesize polymers containing a PEG midblock are limited. In this study, the successful synthesis of a heterofunctional PEG macroinitiator containing both an azoinitiator and an atom transfer radical polymerization (ATRP) initiator is demonstrated. This novel PEG macroinitiator allows the development of elegant synthesis routes for PEG midblock-containing ABC copolymers that does not require protection of initiating sites or polymer end-group postmodification...
November 14, 2017: Macromolecules
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