The effect of commonly used induced condensing agents (ICAs) on the rate of polymerization of ethylene on a supported Ziegler–Natta catalyst in a gas‐phase process is investigated. It is observed that the instantaneous rate of ethylene polymerization is promoted in presence of all ICAs studied. This is attributed to the effect of the heavy ICAs in enhancing the local concentration of ethylene at the active polymerization sites that are dispersed within the growing polymer particles. It is found that the higher the solubility of ICA in the polymer, the greater the observed effect. It is also observed that the enhancement due to the presence of an ICA is greater during the initial phase of the polymerization.
The presence of different commonly used induced condensing agents (ICAs) in the gas phase polymerization of ethylene on the supported catalyst has a significant impact on the crystallinity and the molecular weight distribution of the resulting high density polyethylene. The crystallinity of the polymer is found to be higher in the presence of vaporized n‐pentane or n‐hexane, than in “dry mode” (i.e., with no ICA). This is primarily attributed to the mechanism of crystallization of polymer chains in presence of the solubilized ICA which might act to promote solvent vapor annealing. In addition, vaporized ICA also provokes a significant increase in the weight average molecular weight, with values being estimated at over one million.
A systematic analysis methodology is proposed in order to be able to evaluate the role and the significance of the impact of the physical and chemical phenomena during the gas phase ethylene copolymerization in presence of 1‐pentene and 1‐hexene comonomers in the gas phase composition. In addition, the effect of inert n‐hexane on the instantaneous rate of gas phase ethylene polymerization in the absence and presence of 1‐hexene comonomer and hydrogen is investigated. This, in turn, provides a novel insight on the counter‐effects of the physical and chemical phenomena taking place simultaneously during the gas phase processes for ethylene polymerization in the industrially relevant conditions.
A first‐principles map for the equilibrium morphologies of polymer–inorganic nanocomposites synthesized by miniemulsion polymerization is developed. The predictions are compared with literature results on the effect of the initiator type, surfactant concentration, monomer system, and surface characteristics of the inorganic nanoparticles on the morphology of the nanocomposites. The limitations of the morphology map are also discussed.
A novel symmetrical selenium‐based reversible addition‐fragmentation chain transfer (RAFT) agent, Se,Se’‐dibenzyl carbonodiselenothioate (Se‐RAFT), is synthesized and used in the RAFT polymerization of styrene. The results obtained show that the Se‐RAFT agent is involved in the polymerization of styrene, as evidenced by narrow molar‐mass distributions (/ < 1.6) and the incorporation of the Se‐RAFT moiety into the resultant polymer. The latter is confirmed by aminolysis, NMR spectroscopy, size‐exclusion chromatography (SEC) and UV spectroscopy. This work provides detailed insight into the Se‐RAFT polymerization mechanism. The Se‐RAFT agent is unique in that the stabilizing and leaving groups are identical.
Multiple suspension particles — a new morphology of polymer particles — are generated on the verge of colloidal stability in the course of redox‐initiated aqueous heterophase copolymerization. These particles consist of block copolymers which are arranged in the form of a micrometer‐sized poly(N‐isopropylacrylamide) physical network as scaffold containing nanometer‐sized particles of hydrophobic polymers covalently attached.
Poly(methyl methacrylate)‐block‐poly(4‐vinylpyridine), polystyrene‐block‐poly(4‐vinyl pyridine), and poly(ethylene glycol)‐block‐poly(4‐vinylpyridine) block copolymers are synthesized by successive atom transfer radical polymerization (ATRP), single‐electron‐transfer nitroxide‐radical‐coupling (SET‐NRC) and nitroxide‐mediated polymerization (NMP). This paper demonstrates that this new approach offers an efficient method for the preparation of 4‐vinylpyridine‐containing copolymers.
In this paper, “star anise”‐like anisotropic micelle (AM) from direct aqueous self‐assembly of poly(ethylene oxide)‐block‐poly(p‐dioxanone) amphiphilic diblock copolymer is presented. By adding poly(ethylene imine) (PEI), the AM shows morphological change from “star anise” to swollen sphere. The mechanism of PEI‐triggered morphological transition involving complexation and weakening of crystallizability is revealed.
Three thioxanthone‐based hydrophilic visible photoinitiators (TX‐MPEG350, TX‐MPEG550, and TX‐MPEG750) are prepared and characterized. All of them exhibit excellent water dispersion properties. Real‐time FTIR investigation shows that they can be used as visible photoinitiators for radical polymerization in waterborne systems in the presence and absence of the hydrogen donors. Among them, TX‐MPEG550 has been illustrated as the best hydrophilic visible photoinitiator in the presence of hydrogen donors and would have great potential applications in waterborne visible photocuring systems after carefully investigating the photopolymerization behavior of TX‐MPEGs in different conditions.
Copolymerization of ethylene with 4‐penten‐1‐ol (4P1O) is conducted by using a half‐titanocene catalyst. The incorporation of 4P1O is high as approximately 10 mol%. The assignments of the 13C NMR spectrum and the analysis of the sequence distribution show the existence of not only the alternative structure but also the repeated 4P1O units. The product of the reactive ratios is calculated as ca. 2.
Ordered nanoring arrays are a new pattern of block copolymer thin films generated by spin‐coating of block copolymer reverse micelles on silicon substrates, which can further direct the formation of gold nanoring arrays on block copolymer thin films. Here, it is reported that the cooperation of swelling and coordination can influence the surface pattern of the block copolymer nanospheres. A hexagonally arranged dot pattern can be transformed into a ring pattern on polystyrene‐block‐poly(2‐vinylpyridine) nanospheres, and the new pattern can further direct the decoration of gold nanoparticles by balancing the swelling of the poly(2‐vinylpyridine) chains and the coordination effect between gold ions and the pyridine units.
The preparation of novel nanoparticles is described, which consist of a poly(lactic acid) (PLA) core obtained by the nanoprecipitation method with a shell made of oppositely charged β‐cyclodextrin polymer (poly‐β‐CD) assembled using the layer‐by‐layer technique. Characterization of these nanoparticles is accomplished through dynamic light scattering, ζ‐potential measurements, X‐ray photoelectron spectroscopy and electron microscopy. The release of a loaded lipophilic molecule, benzophenone (BP), is mainly controlled by diffusion of BP and by its host–guest interaction with the β‐CD cavities of the adsorbed poly‐β‐CD. Increasing the number of poly‐β‐CD layers results in a better control of the release through the partition equilibrium between free BP and BP included in the cavities inside the multilayers.
Dithiobenzoates are among the most popular agents for reversible addition‐fragmentation chain transfer (RAFT) polymerization. This is attributed to the better control over molecular weight and end‐group fidelity found in RAFT polymerization of methacrylates and methacrylamides. However, in polymerization of styrenes, acrylates, and acrylamides, their use has diminished, mainly in favour of trithiocarbonates, because of issues with retardation, as well as hydrolytic and thermal instability. This paper critically assesses developments in understanding the mechanism and kinetics of dithiobenzoate‐mediated RAFT polymerization from 2006 to 2013, with specific reference to the choice of reagents, polymerization conditions, side reactions, and factors leading to retardation.
Renewable alternating aliphatic–aromatic copolyesters are obtained through the polycondensation of biobased diacyl chlorides and bisphenols derived from ferulic acid and biosourced diols. The Tg of these thermoplastics can be tailored to closely match those of petroleum‐based poly(ethylene terephthalate) (PET) and also give access to applications requiring polyesters with lower glass‐transition temperatures.
Dynamic crystallization (DC) is a new characterization technique for measuring the chemical composition distribution (CCD) of semicrystalline copolymers. This technique fractionates polymers based on chain crystallizabilities under a constant cooling rate; a solvent is also fed through the column at a constant flow rate during the crystallization to enhance the physical separation of the polymer fractions. In this work, a DC model for ethylene/1‐olefin copolymers on the basis of population balance, crystallization kinetics, and axial dispersion is proposed. This model is found to describe the experimental DC profiles of an ethylene/1‐octene copolymer at various operation conditions very well.
The Cu(I)‐catalyzed azide‐alkyne click polymerization is well developed and broadly applied to the preparation of functional polymers. The removal of copper residues from the resultant polymers is, however, difficult. One way to completely circumvent this difficulty is to develop click polymerization without the use of metallic catalysts, i.e., metal‐free click polymerization (MFCP). Herein, recent efforts towards developing MFCP of activated alkynes and azides, and of activated azides and alkynes, to produce regioregular polytriazoles are summarized, and the properties and applications of the resultant polymers are also briefly discussed.
Desorption of thiol‐based self‐assembled monolayers on gold surfaces makes surface‐initiated atom transfer radical polymerization (SI‐ATRP) challenging and results in reduced density “grafted from” polymer film. In this work, in situ attenuated total reflectance‐Fourier transform infrared (ATR‐FTIR) spectroscopy shows that copper‐based catalysts typically used in SI‐ATRP cause substantial desorption of bound thiol‐based initiator films from gold surfaces. Other reaction conditions factors such as low temperature, presence of radicals, and solvents selection have relatively minor effects in comparison. Indeed, the desorption of initiator films is reduced from more than 80% to about 45% when CuCl catalyst is used for the ATRP of styrene instead of CuBr catalyst. However, the polymerization rate is significantly slower in this case.
A new strategy for the preparation of magnetite/silica/(co)polymer core/shell nanoparticles is described. The reversible addition‐fragmentation chain transfer/macromolecular design via interchange of xanthates (RAFT/MADIX) polymerization agent — xanthate/dithiocarbonate — is covalently anchored to the aminosilica‐coated iron oxide nanoparticles surface by its R‐group. Subsequently, polymerization and copolymerization of vinyl monomers on such synthesized structures are carried out. Fourier transform infrared (FTIR) spectroscopy, UV–vis spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X‐ray diffraction (XRD), energy‐dispersive X‐ray (EDX) analysis, and transmission electron microscopy (TEM) are employed to confirm the grafting and study the chemical composition of the obtained structures.
A novel polymerization mechanism transformation strategy, involving anionic ring‐opening polymerization and photoinduced cationic polymerization, is successfully applied for the synthesis of poly(ethylene oxide)‐graft‐poly(isobutyl vinyl ether) (PEO‐g‐PIBVE). First, poly(ethylene oxide‐co‐ethoxyl vinyl glycidyl ether) [P(EO‐co‐EVGE)] is synthesized by living anionic polymerization. The vinyl moieties of the functional PEO‐based polymer are converted to the hydrogen iodide adduct by photolysis of diphenyliodonium iodide, monitored using NMR spectroscopy. A modified mode of Lewis acid‐catalyzed living cationic polymerization is performed as a “grafting from” method to generate PIBVE segments grafted onto the PEO main chain. Both the intermediates and the final graft copolymers are characterized by gel‐permeation chromatography (GPC) and 1H NMR analysis.
Nonionic aliphatic polymers containing ester and sulfonyl moieties, [poly(ester‐sulfones)s] were found to undergo anode‐selective electrophoresis under electrophoretic deposition conditions. Herein are reported the syntheses of unsaturated nonionic polyesters containing sulfide linkages and double bonds on the polymer backbone via acyclic diene metathesis polymerization using a Grubbs' catalyst. Subsequent oxone oxidation was carried out, affording the corresponding poly(ester‐sulfone), followed by electrophoretic deposition of the unsaturated poly(ester‐sulfone) onto stainless steel. Subsequent UV‐irradiation cured the deposited film, improving the peeling strength of the coating.
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