Initiation, spontaneous

Various acrylates, methacrylates and related compounds have been reported to undergo spontaneous polymerization. 110 A complication in studying thermal polymerization of MMA is the difficulty in eliminating impurity initiated polymerization. The monomer is extremely difficult to purify or retain in a "pure" state. These problems have led some to question whether there is any true spontaneous initiation.323 It is, in any event, clear that the rate of thermal polymerization of MMA is substantially less than that of S at the same temperature (at least 70-fold less at 90 °C).310324... 

Other postulated mechanisms for spontaneous initiation include electron transfer followed by proton transfer to give two monoradicals, hydrogen atom transfer between a charge-transfer complex and solvent,110 and formation of a di radical from a charge-transfer complex, JJ[Pg.111]

However, these observations are not proof of the role of a donor-acceptor complex in the copolymcrization mechanism. Even with the availability of sequence information it is often not possible to discriminate between the complex model, the penultimate model (Section 7.3.1.2) and other, higher order, models.28 A further problem in analyzing the kinetics of these copolyincrizations is that many donor-acceptor systems also give spontaneous initiation (Section 3.3.6.3). 

Automaticity Ability of a cardiac fiber or tissue to spontaneously initiate depolarizations. 

Because the polymerization with the thermal iniferters previously described was performed at a high temperature, some side reactions might be unavoidable, e.g., ordinary bimolecular termination between polymer radicals, disproportionation between a polymer radical and a small radical leading to deactivation of the iniferter site, initiation by the radical generated from the iniferter sites, rearrangements of the structure of the iniferter sites, and spontaneous initiation of polymerization. 

The polymerization of St with 56 as the initiator is considered to proceed via a reaction mechanism in Eq. (56), being identical to the models in Eqs. (18) and (20). The structure of both chain ends of the resulting polymer was confirmed by NMR using the deuterated St as the monomer. The polymerization with BPO and TEMPO without isolation of the adduct would also proceed via a similar path. In the absence of BPO, it has been reported that the radicals produced by spontaneous initiation according to the Mayo mechanism react with TEMPO to yield the adducts, and then they initiate polymerization [206]. 

Elen 2.01 +1.455 = -0.56 V This reaction is not even spontaneous initially. 

Holyoake TL, Jiang X, Jorgensen HG et al. Primitive quiescent leukemic cells from patients with chronic myeloid leukemia spontaneously initiate factor independent growth in vitro in association with up-regulation of expression of interleukin 3. Blood 2001 97 720 728. 

Non-Steady State Equations with Correction for Spontaneous Initiation and First-Order Termination. Thoroughly purified hydrocarbons should exhibit a square-root dependence of oxidation rate on initiation rate, R we found, however, that even if this behavior is obtained with Ri of the order of 10 8 mole per liter per sec., deviations may occur with the low rates of initiation used in the non-steady state measurements (R 10 n). Also, spontaneous initiation of the order of R — 10 12 may occur. If we assume that the deviations can be described as a constant first-order termination, we can derive corrected formulas for the nonsteady state behavior upon adding a small amount of inhibitor AH or initiator AR, as follows. 

Initial condition spontaneous initiation Rf, first-order termination constant X ... 

Critical size for spontaneous detonation) 140 (Spontaneous ignitions) 146 (Spontaneous expin caused by traces of AgN which took place at Linden Lab is discussed) 154 (Spontaneous initiation during growth of a cryst in soln observed by Dr J.V.R. Kaufman for a-PbNjj and by... 

Addnl information on Frank-Kamenetsky formulation) 13e (Description of spontaneous initiation listed in Ref 4, p 154) 7) T.B. 

Initiation, Spontaneous. This is really a misnomer. What it refers to is the self-heating of an explosive as a result of autocatalytic decomposition eventually leading to a thermal explosion. Spontaneous initiation may also occur during crystal growth eg in Lead Azide see Detonation (and Explosion), Spontaneous in Vol 4, pp D561-563... 

Since the reaction of nitric acid alone with a fuel such as petrol or paraffin occurs fairly slowly with a long induction period (longer than 0.1 sec) various substances are added to the nitric acid or the hydrocarbon component to speed up the reaction or induce its spontaneous initiation. 

Haissaguerre M, et al. Spontaneous initiation of atrial fibrillation by ectopic beats originating in the pulmonary veins. N Engl J Med 1998 339(I0) 659 666. 

This chain process requires an initiation step. In a few systems a thermal (spontaneous) initiation is observed. One of the methods consists in the formation of the radical anion of the substrate by reaction with alkali metals in liquid ammonia. Electrochemical initiation is an approach that has been successful in a considerable number of cases with aromatic and heteroaromatic substrates [14]. Other possibilities include the use of Fe+2 [15-18], Sml2 [19], or Na(Hg) [20]. However, the most extensively used method is the photoinitiation, and it has proven extremely suitable for synthetic purposes Even though it is a widely used initiation method, there are not many mechanistic studies of this step. 

The outcome of charge-transfer polymerizations has been systematized by Iwatsuki and Yamashita in their penetrating early review [130]. They arrived at a correlation of polymerization behavior with the value of the EDA complex equilibrium constant, Keq, With weak donor and acceptor olefins, no spontaneous polymerization takes place, while the addition of a radical initiator results in a random or an alternating copolymer depending on the value of Keq. As the donor and acceptor strength of the olefins increases, spontaneous initiation rates for radical copolymerization increase and with even stronger donor and acceptor olefins, ionic homopolymerization takes place (cationic and/or anionic). 

Thermal or spontaneous initiation is possible when the nucleophile is a powerful reducing agent. Even though light is not necessary in these cases, it often provides significant rate acceleration. 

The above subject has been selected as an example of the design of new polymerization reactions. It is concerned with a concept of copolymerization by spontaneous initiation and subsequent propagation via zwitterion intermediates. This copolymerization, which was invented and has been developed by the author, is called no catalyst copolymerization . It is very characteristic since usual polymerization reactions require either an initiator or a catalyst. 

A series of the above reactions (Eq. (19) to (22)) gives rise to the formation of alternating copolymers. Thus, the above new copolymerization has two characteristics, the one is the spontaneous initiation without any catalyst and the other is the production of a 1 1 alternating copolymer. 

Apparent transfer constants for selected compounds in the polymerization of styrene [42, 43], Spontaneous initiation at 333 K. 

Several types of zwitterionic polymerization reactions have been identified. One type is spontaneously initiated upon mixing a nucleophilic monomer with an electrophilic monomer. Another type involves the thermal generation of a reactive zwitterion. Finally, zwitterions that are sufficiently stable to be isolated have been polymerized. 

A. Spontaneous Initiated Alternating Copolymerization of Nucleophilic-Electrophilic Monomer Pairs... 

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