Search results for "Dispersity"
showing 10 items of 207 documents
CVD synthesis of carbon spheres using NiFe-LDHs as catalytic precursors: structural, electrochemical and magnetoresistive properties
2016
The gram-scale synthesis of carbon spheres with a diameter of ca. 740 nm has been achieved by means of a chemical vapour deposition method using NiFe-layered double hydroxides as a solid catalytic precursor. The presence of the catalyst (FeNi3) allows controlling the final size distribution, resulting in a monodisperse sample. Their structural properties exhibited a high degree of graphitization according to their ID/IG ratio. In addition, their morphological features were unveiled by FIB-SEM and HRTEM, showing that they are formed by solid inner cores, and presenting labile chain-like structures due to accretion procedures. The solution and posterior sonication of the samples in toluene ga…
Polyester and Ester Functionalized Dendrimers
2000
Demand for smart and functional materials has raised the importance of the research of dendritic (Greek = tree-like) molecules in organic and polymer chemistry due to their novel physical and mechanical properties. The properties of linear polymers as well as small discrete molecules are combined in this new architectural class of macromolecules, that can be divided into two families: dendrimers and hyperbranched macromolecules, that differ in their branching sequences. Dendrimers contain symmetrically arranged branches emanating from a core molecule together with a well-defined number of end groups corresponding to each generation. This results in an almost monodisperse three-dimensional g…
Surfactant-Free Emulsion Polymerization of Various Methacrylates: Towards Monodisperse Colloids for Polymer Opals
2004
A systematic investigation of the surfactant-free emulsion polymerization (SFEP) on three different methacrylates (MMA, tert-butyl methacrylate and 2,2,2-trifluoro ethyl methacrylate) is described to obtain monodisperse colloids for the preparation of artificial polymer opals. The experimental results are in agreement with a model, in which seed particles are formed very early during the polymerization process. The particles are formed very early during the polymerization process. The particles grow afterwards into the colloids until all monomer is consumed. This gives rise to a linear relationship between the volume of the colloids and the ratio of monomer to water in the reaction batch. T…
Carbanions on Tap – Living Anionic Polymerization in a Microstructured Reactor
2008
The paper describes the living anionic polymerization of styrenes to homo- and diblock copolymers in continuous flow, using a microstructured mixing set-up ("microreactor"). Reaction times and experimental effort are significantly reduced compared to classical batch methods that often require stringent reaction conditions and strict drying of the apparatus by "break-seal" and "high vacuum" techniques. In continuous flow, residual impurities can be removed by purging the reactor with monomer and initiator solution before polymer samples are collected at the device outlet on a scale of up to 200 g.h -1 . Facile molecular weight adjustment is achieved by variation of the flow rates of initiato…
Particle Penetration into Polydisperse Polymer Brushes: A Theoretical Analysis
2017
Based on theoretical analysis, the effect of polydispersity on particle penetration into polydisperse polymer brushes is investigated. Three different polydispersities representing sharp, moderate, and extremely wide chain length distributions are chosen, since the corresponding explicit expressions of brush density at these polydispersities are available. To simplify the discussion, this study is restricted to spherical particles of small size which ensure that the particle insertion only causes local conformational perturbations. By analyzing the particle distribution, it is found that polydispersity always facilitates particle penetration. This prediction is confirmed by analyzing the su…
Crystallization and melting of fractions of branched polyethylene
1983
Effects of the molecular weight on the crystallization behaviour of branched polyethylene become observable if isothermal crystallization is studied at temperatures near to the melting end. Crystallinities decrease with decreasing molecular weight. Thicknesses of lamellae grown during isothermal crystallization are independent of the molecular weight. They depend only on temperature. Compared to the effect of the branches polydispersity gives only a minor contribution to the broadening of the crystallization and melting range of low density polyethylene.
Synthesis and NMR characterization of new poly(ethoxyalkyl) maleates
1994
Polymerizable surfactants derived from maleic anhydride have been synthesized. The hydrophilic part is obtained by a controlled ethylene oxide polymerization according to a new heterogeneous catalytic process. Some maleates derivatives have been obtained and fully characterized by 1H and 13C NMR. Their cmc were also measured. Some of them have been engaged in styrene emulsion polymerization in which monodisperse latex particles have been produced.
Polydisperse polymer brushes: internal structure, critical behavior, and interaction with flow
2016
We study the effect of polydispersity on the structure of polymer brushes by analytical theory, a numerical self-consistent field approach, and Monte Carlo simulations. The polydispersity is represented by the Schulz-Zimm chain-length distribution. We specifically focus on three different polydispersities representing sharp, moderate and extremely wide chain length distributions and derive explicit analytical expressions for the chain end distributions in these brushes. The results are in very good agreement with numerical data obtained with self-consistent field calculations and Monte Carlo simulations. With increasing polydispersity, the brush density profile changes from convex to concav…
Linear-Hyperbranched Amphiphilic AB Diblock Copolymers Based on Polystyrene and Hyperbranched Polyglycerol
2005
A convenient three-step strategy has been developed for the preparation of well-defined amphiphilic, linear hyperbranched block copolymers by hypergrafting. The synthetic procedure is based on a combination of carbanionic polymerization with the alkoxide-based controlled ring-opening multibranching polymerization of glycidol. A linear AB diblock copolymer polystyrene-block-polybutadiene (PS-b-PB) with narrow polydispersity was obtained by anionic copolymerization. Subsequent hydroxylation by hydroboration led to PS 508 -b-(PB-OH) 56 , used as macro--initiator for the polymerization of glycidol under slow monomer addition conditions.
Using Copolymers to Design Tunable Stimuli-Reponsive Brushes
2020
Recently, a new design for switch sensors has been proposed that exploits a conformational transition of end-grafted minority adsorption-active homopolymers in a monodisperse polymer brush [Klushin...