Search results for "Ionic polymerization"

Carbanionic Polymerization: Kinetics and Thermodynamics

1989

For a kinetic analysis, the process of anionic polymerization has to be divided into at least three main reactions common to all types of polymerization (equations 1–3). I* denotes initiator, M monomer, Pi* and Pi′ an active or inactive polymer chain of degree of polymerization i, respectively, and X a terminating agent.

Solid-state polymerization of oxetanes. II. Investigation of the growth of the polymer phase as related to the mechanism of polymerization

1973

The radiation-induced solid-state polymerization of 3,3-bischloromethyloxetane (BCMO) was investigated by direct observation of the development of the morphology of the growing polymer phase in single crystals of the monomer. Electron microscopy shows that the polymerization gives rise to amorphous polymer in the first step. The polymer forms irregular platelets which aggregate into larger units without reflecting the crystalline order of the monomer. Subsequent to polymerization, the amorphous polymer crystallizes to the β-modification of poly-BCMO. If the partially polymerized crystals are extracted by solvents of the monomer, crystallization of the polymer is enhanced, and morphological …

Initiatoren für die polymerisation des trioxane. 20. Mitt. über polyoxymethylene1

1963

Die Polymerisation des Trioxans bei 60°C in Cyclohexan mit verschiedenen kationischen Initiatoren wurde untersucht. Die aktivsten Initiatoren sind Acetylperchlorat, Perchlorsaure, FeCl3 und SnCl4. Die Molekulargewichte der erhaltenen Polyoxymethylene sind bei den aktivsten Initiatoren am hochsten. Der Einflus der ubertragung durch Wasser und der kinetischen Kettenlange auf die Molekulargewichte wird diskutiert. Wahrend der Polymerisation kann durch den Initiator eine Spaltung bereits gebildeter Makromolekule erfolgen, welche die Molekulargewichte stark reduziert. Die Frage der Cokatalyse bei der kationischen Polymerisation des Trioxans mit Ansolvosauren wurde untersucht. Bei der Polymerisat…

What Limits the Molecular Weight and Controlled Synthesis of Poly(3-alkyltellurophene)s?

2016

Polytellurophenes are an emerging class of conjugated polymers; however, their controlled polymerization leading to high molecular weight materials has been a major challenge. Here we present a systematic investigation of the synthesis of poly(3-alkyltellurophene)s using the catalyst transfer polycondensation methodology. Learning that previous syntheses were limited by both polymerization reaction kinetics and polymer solubility, we design new tellurophene monomers to overcome these limitations. Controlled polymerization behavior up to Mn = 25 kDa, chain extension, block copolymerization, external initiation, and well-defined end groups are demonstrated for poly(3-alkyltellurophene)s with …

Kinetic Analysis of “Living” Polymerization Processes Exhibiting Slow Equilibria. 5. Effect of Monomer Transfer in Cationic Polymerization and Simila…

1996

This work deals with the kinetics of polymerization processes with chain transfer to monomer and reversible formation of dormant species. Such a mechanism is typical for cationic polymerization in the presence of Lewis acids as co-initiators. The expressions of number- and weight-average degrees of polymerization and polydispersity index are derived rigorously for a mechanism with free ions as the active species, but it is also applied to other mechanisms, e.g., ion pairs as active species. Plots of polydispersity index versus monomer conversion can be easily computed on a PC computer even though the expressions for the weight-average degree of polymerization and the concentration of residu…

1980

Using a bifunctional initiator such as the tetrameric dianion of α-methylstyrene for the anionic polymerization of methyl methacrylate the rate constant is found to increase with conversion approaching that observed with a monofunctional initiator while the tacticity of the polymers obtained changes from that of an almost ideally atactic to a highly syndiotactic polymer. The results are explained by the assumption of an intramolecular association of the two terminal ion pairs yielding a new active species and gradually dissociating with increasing degree of polymerization of the chain. Using a polymeric dianion of α-methylstyrene as an initiator the association phenomenon is not observed.

Some kinetic effects in the polymerization of 1,3,5-trioxane

1960

Ordering kinetics in synthetic Mg(Al,Fe3+)2O4 spinels: Quantitative elucidation of the whole Al-Mg-Fe partitioning, rate constants, activation energi…

2014

A novel procedure, based on the application of the kinetics simulator Gepasi, has been successfully applied for modeling the cation ordering process in two synthetic Mg(Al2-yFe3+y)O4 spinels (y~ 0.39 and 0.54, samples F39 and F54, respectively). The kinetic profiles suggested a two-stage mechanism, with rapid inter-site exchange of Fe3+ with Mg followed by slow exchange of Al with Mg. The trial to apply the classical approaches, based on the explicit solutions of the differential equations corresponding to single-cation (Sha-Chappel model) or two-cation (Müller model) exchange reactions, proved not feasible in the whole time range, thus implying a lack of information about the exchange proc…

Molecular organization of a water-insoluble iridium(III) complex in mixed monolayers.

2007

Abstract In this work, organized mixed monolayers containing a cationic water-insoluble iridium(III) complex, Ir-dye, [Ir(ppy)2(tmphen)]PF6, (tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline, and ppy = 2-phenylpyridine), and an anionic lipid matrix, DMPA, dimyristoyl-phosphatidic acid, with different molar proportions, were formed by the co-spreading method at the air–water interface. The presence of the dye at the interface, as well as the molecular organization of the mixed films, is deduced from surface techniques such as π – A isotherms, Brewster angle microscopy (BAM) and reflection spectroscopy. The results obtained remark the formation of an equimolar mixed film, Ir-dye/DMPA = 1:1. B…

D2/H2 adsorption selectivity on FAU zeolites at 77.4 K: Influence of Si/Al ratio and cationic composition

2018

Abstract Equilibrium D2/H2 adsorption selectivity was determined at 77.4 K below 1000 hPa for a series of FAU type zeolites X exchanged with different cations (Li+, Na+, K+, Mg2+, Ca2+, Ba2+ and Mn2+). In addition NaY, DAY (dealuminated Y) and pure silica CHA and MFI zeolites were studied. Two experimental approaches were used to determine the D2/H2 adsorption selectivity: direct determination at the thermodynamic equilibrium from manometric coadsorption experiments and calculations by Ideal Adsorbed Solution Theory (IAST) from single gas adsorption isotherms. While these two approaches are not in quantitative agreement, they reveal similar trends. At low loading (  MnX > LiX > CaX ≈ NaX > …