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Macromolecules

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https://www.readbyqxmd.com/read/30057430/grafting-from-a-hybrid-dna-covalent-polymer-by-the-hybridization-chain-reaction
#1
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
https://www.readbyqxmd.com/read/30018463/linear-viscoelasticity-of-weakly-hydrogen-bonded-polymers-near-and-below-the-sol-gel-transition
#2
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
https://www.readbyqxmd.com/read/30018462/effect-of-self-assembly-of-oxalamide-based-organic-compounds-on-melt-behavior-nucleation-and-crystallization-of-isotactic-polypropylene
#3
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
https://www.readbyqxmd.com/read/30018461/effects-of-surfactant-and-urea-on-dynamics-and-viscoelastic-properties-of-hydrophobically-assembled-supramolecular-hydrogel
#4
Marko Mihajlovic, Hans M Wyss, Rint P Sijbesma
Physically associated hydrogels based on strong hydrophobic interactions often have attractive mechanical properties that combine processability with elasticity. However, there is a need to study such interactions and understand their relation to the macroscopic hydrogel properties. Therefore, we use the surfactant sodium dodecyl sulfate (SDS) and urea as reagents that disrupt hydrophobic interactions. The model hydrogel is based on a segmented copolymer between poly(ethylene glycol) (PEG) and hydrophobic dimer fatty acid (DFA)...
July 10, 2018: Macromolecules
https://www.readbyqxmd.com/read/29915431/a-vinyl-ether-functional-polycarbonate-as-a-template-for-multiple-postpolymerization-modifications
#5
Sangho Cho, Gyu Seong Heo, Sarosh Khan, Jessica Huang, David A Hunstad, Mahmoud Elsabahy, Karen L Wooley
A highly-reactive vinyl ether-functionalized aliphatic polycarbonate and its block copolymer were developed as templates for multiple post-polymerization conjugation chemistries. The vinyl ether-functional six-membered cyclic carbonate monomer was synthesized by a well-established two-step procedure starting from 2,2-bis(hydroxymethyl)propionic acid. An organobase-catalyzed ring-opening polymerization of the synthesized monomer afforded polycarbonates with pendant vinyl ether functionalities (PMVEC). The vinyl ether moieties on the resulting polymers were readily conjugated with hydroxyl- or thiol-containing compounds via three different post-polymerization modification chemistries - acetalization, thio-acetalization, and thiol-ene reaction...
May 8, 2018: Macromolecules
https://www.readbyqxmd.com/read/29805184/synthesis-of-high-molecular-weight-poly-glycerol-monomethacrylate-via-raft-emulsion-polymerization-of-isopropylideneglycerol-methacrylate
#6
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
#7
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
#8
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
#9
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
#10
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
#11
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
#12
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/29983451/protection-of-opening-lids-very-high-catalytic-activity-of-lipase-immobilized-on-core-shell-nanoparticles
#13
Xuefei Sun, Weipu Zhu, Krzysztof Matyjaszewski
Various hydrophobic supports have been used for lipase immobilization since the active site of lipase can be opened in a hydrophobic environment. Nevertheless, the increase of lipase activity is still limited. This study demonstrates a hyperactivation-protection strategy of lipase after immobilization on poly( n -butyl acrylate)-polyaldehyde dextran (PBA-PAD) core-shell nanoparticles. The inner hydrophobic PBA domain helps to rearrange lipase conformation to a more active form after immobilization into the PAD shell...
January 23, 2018: Macromolecules
https://www.readbyqxmd.com/read/29910511/the-multifaceted-role-of-methylaluminoxane-in-metallocene-based-olefin-polymerization-catalysis
#14
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
#15
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
#16
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
#17
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
#18
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
#19
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
#20
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
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