Anionic polymerization radical anions

We have seen a number of reactions in which alkene derivatives can be polymerized. Radical polymerization (see Section 9.4.2) is the usual process by which industrial polymers are produced, but we also saw the implications of cationic polymerization (see Section 8.3). Here we see how an anionic process can lead to polymerization, and that this is really an example of multiple conjugate additions. 

Contrary to the high selectivity shown in cationic and anionic polymerization, radical initiators bring about the polymerization of almost any carbon-carbon double bond. Radical species are neutral and do not have stringent requirements for attacking the re-bond or for the stabilization of the propagating radical species. Resonance stabilization of the propagating radical occurs with almost all substituents, for example... 

By using the aluminum porphyrin-Lewis acid system, we attempted the synthesis of a narrow MWD block copolymer from oxetane and methyl methacrylate (MMA). Methacrylic monomers can be polymerized radically and anioni-cally but not cationically, so a block copolymer of oxetane and methyl methacrylate has never been synthesized. As already reported, methacrylic monomers undergo accelerated living anionic polymerization with the (TPP)AlMe (1, X= Me)-3e system via a (porphinato)aluminum enolate as the growing species. 

The room-temperature chemistry of high-surface-area CoO-MgO solid solutions is dominated by the adsorption of CO on edges and steps. Co-ordinatively unsaturated Co2+ and O2 ions react primarily as 02 Co2+02 triplets with formation of [(CCh CoCO]2- species. In samples with high Co contents, the large amounts of clustered cobalt guest species are easily reduced by CO, even at room temperature, with formation of Co(CO)4 and carbonate-like species (377). The formation of polymeric radical anions of CO on high-surface-area CoO-MgO solid solution has also been reported (378). 

Two typra of methods were u d in the cationic polymerization of hetraocycles to determine the concentration of the Rowing species. The first type is based on methods used in free-radical polymerization (radical trapping) and in anionic polymerization when the macroanions are quantitatively converted into the stable end groups whose concentrations can then be measured. 

Problem 8.1 Contrary to the high selectivity shown in cationic and anionic polymerization, radical initiators can bring about the polymerization of almost any carbon-carbon double bond. Explain, giving reasons. 

Styrene can be polymerized radically either thermally or by using free-radical initiators, anionically or cationical ly. Thermally the reaction is initiated by a Diels Alder adduct in the following manner (2) ... 

The yield of the absorption at 320 m/x was found to rise with concentration in a way suggesting that it is formed by anionic process—e.g., by protonation of a styrene anion by its geminate partner (31). If it is a polymerizing radical, then the rate constant for addition of the benzyl-type radical to styrene must be at least KP-lOW-1 sec.-1. The yield of the observable anion seemed much less dependent on concentration, which is consistent with the view that it is formed by those electrons (G.— 0.2) which escape from the spur. Absorptions with peaks close to 320 m/x are seen for all the other solvents above, but the component at the longer wavelength is seen only with the aliphatic hydrocarbons. For methanol solutions this may be because of rapid protonation. 

All kinds of polymerization (radical, anion, cation, and condensation) can be employed for molecular imprinting. The only requisite is that the polymerization can satisfactorily occur under the conditions where all the components (the templates, the crosslinking agents, non-cova-... 

Contrary to the high reactivity of the active centers in cationic and anionic polymerizations, radical polymerizations are tolerant to many functionalities. It has been possible to polymerize a wide range of functional monomers such as substituted styrenes, functional acrylates and substituted acrylamide. 

Schlenk s hydrocarbon and Dougherty s polymeric radical anion... 

Initiators, accelerators, and inhibitors of cyanoacrylate polymerization are used to modify the cure speed and storage stability of these adhesives. They can also be used to broaden the range of materials which can be bonded with cyanoacrylates. Initiators are those materials which are capable of polymerizing cyanoacrylate esters upon contact. These are, therefore, applied either to the substrate surface ( surface primers ), or mixed with the adhesive just prior to application. Accelerators are materials which do not cause polymerization on contact with monomer, but which increase the cure rate once the adhesive is applied. These chemicals are most often compounded with the monomer in the adhesive formulation. The distinction between these two classes can be blurred, as some additions will not cause immediate polymerization on contact but will shorten shelf life in the long run. Anionic polymerization inhibitors are Lewis or Bronsted acids which retard or completely inhibit anionic polymerization. Radical inhibitors prevent polymerization by adventitious, radical sources and are used to prolong the storage stability of the adhesive they generally do not affect cure speed. 

Synthetic organic polymers are commonly formed via one of three possible mechanistic pathways radical polymerization, anionic polymerization, or cationic polymerization. Radical polymerization will be discussed in Chapter 11 and anionic polymerization will be discussed in Chapter 27. In this section, we will briefly introduce cationic polymerization. 

Dimethyl-1,3-butadiene is produced by dehydration of pinacol, which in turn is made by reductive coupling of acetone, followed by purification via sulfur dioxide adducts [313]. It can be polymerized radically (emulsion polymerization), anionically, cationically, or by coordinative catalysts [314-319]. Due to the sterical hindrance of two methyl groups. 

Acrolein, a member of the family of the polymerizable 2-alkenales and 2-alkenones, is provided with an extraordinary tendency for polymerization. Therefore, it may only be stored in the presence of a stabilizer (e.g., hydrochinone) in the absence of light, air, and moisture because of spontaneous polymerization. Even small amounts of initiator have the ability to force acrolein polymerization radically, anionically, or cationically, partly in an explosive manner. According to the existing reaction conditions and the catalysts used, it is possible to attain polymers of completely different shapes with characteristic features [9,13,35]. 

Method of synthesis produced by emulsion polymerization, solution polymerization and bulk polymerization radical initiation is used (Including living polymerization methods), but anionic polymerization of MMA can also be performed ... 

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