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Inhibition ionic polymerization

Aromatic nitro compounds inhibit radical polymerization. However, they do not seem to inhibit ionic polymerization [137]. On the contrary Rumanian authors reported [190] that nitrobenzene as welt as nitromethane and nitro ethane increase the rate of cationic polymerization of W-vinylcarbinol. [Pg.420]

The nature of the gegen ion is probably of the greatest importance in determining the rate of propagation in ionic polymerization. However, it is not clear whether the presence of the gegen ion enhances or inhibits the propagation. One may argue that the... [Pg.159]

Water, alcohols, ethers, or amines can cause inhibition of ionic polymerization. However, these substances can act in different ways according to their concentration. For example, in polymerizations initiated by Lewis acids (BF3 with isobutylene) or organometallic compounds (aluminum alkyls), water in small concentrations behaves as a cocatalyst, but in larger concentrations as an inhibitor (reaction with the initiator or with the ionic propagating species). [Pg.66]

Cationic cure mechanisms are an alternative approach to uv curing. This involves the photogeneration of ions, which initiate ionic polymerization. This process is not subject to oxygen inhibition, as are some of the free radical mechanisms. Cationic cure mechanisms generally also provide less shrinkage and improved adhesion. The disadvantages are that the photoinitiators are sensitive to moisture and other basic materials. The acidic species can also promote corrosion. As a result, the vast majority of uv formulations are acrylate-based and cure by a free radical mechanism. [Pg.259]

Electron micrograph of inhibited styrene polymerized in a non-ionic (Neodol 91-5) microemulsion system (xl280). Reproduced with permission from Ref. 24, Figure 2. Copyright 1988 John Wiley Sons. [Pg.75]

In the artificial world of a test tube, experimenters can start the polymerization process by adding salts to G-actln or can depolymerize F-actin by simply diluting the filaments. Cells, however, must maintain a nearly constant cytosolic ionic concentration and thus employ a different mechanism for controlling actin polymerization. The cellular regulatory mechanism Includes several actin-binding proteins that either promote or Inhibit actin polymerization. Here, we consider two such proteins that have been isolated and characterized. [Pg.786]

METHYL-l-PHENYL-ETHYLENE (98-83-9) C9H10 Flammable liquid. Forms explosive mixture with air [explosion limits in air (vol %) 0.9 to 6.1 flash point 129°F/54°C autoignition temp 1066°F/574°C Fire Rating 2], Easily polymerizable. Unless inhibited, forms unstable peroxides. Reacts with heat and/or lack of appropriate inhibitor concentration. Reacts with catalysts for vinyl or ionic polymerization, such as aluminum, iron chloride or 2,5-dimethyl-2,5-di(ieri-butylperoxy)hexane. Violent reaction with strong oxidizers, butyl lithium, oleum, xenon tetrafluoride. Incon atible with acids. The uninhibited monomer vapor may block vents and confined spaces by, forming a solid polymer material. Attacks aluminum and copper. On small fires, use dry chemical powder (such as Purple-K-Powder), foam, or CO2 extinguishers. [Pg.726]

An important characteristic of ionic polymerization is that the propagation rate coefficients are several orders of magnitude higher than for free-radical polymerization. In the equation fct[X] is the bimolecular termination rate coefficient multiplied by the impurity concentration. This equation shows that the rate of polymerization is proportional to the first power of initiation rate, i.e., to the first power of dose rate. Water is a common chain breaker of cationic polymerization since it replaces the cation by a hydroxonium ion. As a proton donor it also inhibits the anionic polymerization... [Pg.1305]

Ionic Polymerization Ionic chain polymerizations can also be initiated with the aid of Vis/UV light although, as in the case of free-radical photopolymerization, the light serves only as an initiating tool. Most studies on ionic photopolymerization have focused on cationic polymerization, which proceeds rapidly and is not inhibited by oxygen [18,21-24]. Moreover, cationic photopolymerization is apt to polymerize monomers such as vinyl ethers, oxiranes (epoxides), and other heterocyclic compounds that do not polymerize via a free-radical mechanism (Table 3.9). [Pg.139]

Lipophilic ion exchangers traditionally used for polymeric membrane preparation are the anionic tetraphenylborate derivatives and the cationic tetraalkylammonium salts. The charges on both lipophilic ions are localized on a single (boron or nitrogen) atom, but the steric inaccessibility of the charged center, due to bulky substituents, may inhibit ion-pair formation in the membrane and provide, when necessary, non-specific interactions between ionic sites and sample ions. [Pg.123]

Anything that breaks the chain by converting the active chain-carrying species into an ordinary uncreactive molecule inhibits the reaction, and since the chains are often long an inhibitor may be effective in very small traces. The chain-starting catalysts may also be effective in very small amounts provided that no inhibitor is also present. The fact that a reaction is a chain reaction sensitive to small amounts of catalysts and inhibitors does not necesssarily mean that it is a radical chain, but the nature of the substances effective as catalysts or inhibitors will usually differentiate a radical chain from an ionic one. An example of an ionic chain reaction is the polymerization of an olefin-Lewis acid system when water is added as a co-catalyst. Water is so very effective that it is suspected that the polymerization observed in some cases with the driest obtainable reaction mixtures is due to the presence of minute and unavoidable amounts of water. [Pg.248]

The control via activation or inhibition of the rate(s) of an enzyme-catalyzed reaction(s). This control includes the increase or decrease in the stability or half-life of the enzyme(s). There are many different means by which control can be achieved. These include 1. Substrate availability and reaction conditions (e.g., pH, temperature, ionic strength, lipid interface activation) 2. Magnitude of Vraax sud valucs) 3. Activation (particularly, feedforward activation) 4. Isozyme formation 5. Com-partmentalization and channeling 6. Oligomerization/ polymerization 7. Feedback inhibition and cooperativity (particularly, allosterism and/or hysteresis) 8. Covalent modification and 9. Gene regulation (induction repression)... [Pg.615]

Limited local inhibition of these transporters by using polymeric inhibitors could reduce such systemic risks and side effects. Efflux pump modulating polymers and surfactants mentioned in this review have been distinguished between nonionic, ionic and thiolated polymers. [Pg.128]


See other pages where Inhibition ionic polymerization is mentioned: [Pg.160]    [Pg.251]    [Pg.237]    [Pg.53]    [Pg.608]    [Pg.725]    [Pg.805]    [Pg.973]    [Pg.108]    [Pg.11]    [Pg.47]    [Pg.322]    [Pg.79]    [Pg.639]    [Pg.141]    [Pg.318]    [Pg.322]    [Pg.619]    [Pg.356]    [Pg.470]    [Pg.388]    [Pg.24]    [Pg.127]    [Pg.2251]    [Pg.156]    [Pg.467]    [Pg.17]    [Pg.514]    [Pg.248]   
See also in sourсe #XX -- [ Pg.388 ]

See also in sourсe #XX -- [ Pg.388 ]




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Ionic polymerization

Ionic polymerizations polymerization

Polymerization inhibited

Polymerization inhibition

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