Anionic polymerization addition

As all addition polymerizations, anionic polymerization proceeds in three steps initiation, propagation and termination13. ... 

Addition polymerization (anionic polymerization is given as an example)... 

The addition polymerization of a vinyl monomer CH2=CHX involves three distinctly different steps. First, the reactive center must be initiated by a suitable reaction to produce a free radical or an anion or cation reaction site. Next, this reactive entity adds consecutive monomer units to propagate the polymer chain. Finally, the active site is capped off, terminating the polymer formation. If one assumes that the polymer produced is truly a high molecular weight substance, the lack of uniformity at the two ends of the chain—arising in one case from the initiation, and in the other from the termination-can be neglected. Accordingly, the overall reaction can be written... 

The active centers that characterize addition polymerization are of two types free radicals and ions. Throughout most of this chapter we shall focus attention on the free-radical species, since these lend themselves most readily to generalization. Ionic polymerizations not only proceed through different kinds of intermediates but, as a consequence, yield quite different polymers. Depending on the charge of the intermediate, ionic polymerizations are classified as anionic or cationic. These two types of polymerization are discussed in Secs. 6.10 and 6.11, respectively. 

Addition polymerization through anionic active species. This is discussed in the next section. 

Anionic Polymerization. Addition polymerization may also be initiated and propagated by anions (23—26), eg, in the polymerization of styrene with -butyUithium. The LL gegen ion, held electrostatically in... 

Polymerization to Polyether Polyols. The addition polymerization of propylene oxide to form polyether polyols is very important commercially. Polyols are made by addition of epoxides to initiators, ie, compounds that contain an active hydrogen, such as alcohols or amines. The polymerization occurs with either anionic (base) or cationic (acidic) catalysis. The base catalysis is preferred commercially (25,27). 

Proliferous Polymerization. Eady attempts to polymerize VP anionicaHy resulted in proliferous or "popcorn" polymerization (48). This was found to be a special form of free-radical addition polymerization, and not an example of anionic polymerization, as originally thought. VP contains a relatively acidic proton alpha to the pyrroHdinone carbonyl. In the presence of strong base such as sodium hydroxide, VP forms cross-linkers in situ probably by the following mechanism ... 

Addition polymerization is employed primarily with substituted or unsuhstituted olefins and conjugated diolefins. Addition polymerization initiators are free radicals, anions, cations, and coordination compounds. In addition polymerization, a chain grows simply hy adding monomer molecules to a propagating chain. The first step is to add a free radical, a cationic or an anionic initiator (I ) to the monomer. For example, in ethylene polymerization (with a special catalyst), the chain grows hy attaching the ethylene units one after another until the polymer terminates. This type of addition produces a linear polymer ... 

A corresponding anionic mechanism in the presence of a strong base (or electron donor) is plausible. Other cyclic compounds may be susceptible to polymerization by similar ionic mechanisms. Inasmuch as the growth step must be extremely rapid, a chain reaction is indicated and classification with vinyl-type addition polymerizations should be appropriate in such cases. 

Chain-reaction mechanisms differ according to the nature of the reactive intermediate in the propagation steps, such as free radicals, ions, or coordination compounds. These give rise to radical-addition polymerization, ionic-addition (cationic or anionic) polymerization, etc. In Example 7-4 below, we use a simple model for radical-addition polymerization. 

Addition polymerization may proceed through a free radical, cationic or anionic process. Condensation polymers, on the other hand, are formed by elimination of small molecules like that of water, alcohol or ammonia in the reaction of monomeric units, e.g. 

The early, independent work of Starks, Markosa and Brandstrom from ca. 1965-1969, brought into focus with Starks classical paper in 1971, showed PTC to be potent and versatile synthetic tool.[1-4] Since that time, the well-documented investigations of PTC have been massive and vigorous.[5-7] In polymer chemistry PTC was effectively exploited first in anionic addition polymerization and more recently has been extended to condensation polymerization.[5,8-9] However, until a very few years ago, the use of solid-liquid PTC systems in polycondensation has for the most part escaped this intensive scrutiny. Consequently, some time ago we began a rather broad study into the use of solid-liquid PTC to effect polycondensations.[10]... 

Chapters 5 through 7 deal with polymers formed from chain-growth polymerization. Chain-growth polymerization is also called addition polymerization and is based on free radical, cationic, anionic, and coordination reactions where a single initiating species causes the growth of a polymer chain. 

Polymerization reactions can proceed by various mechanisms, as mentioned earlier, and can be catalyzed by initiators of different kinds. For chain growth (addition) polymerization of single compounds, initiation of chains may occur via radical, cationic, anionic, or so-called coordinative-acting initiators, but some monomers will not polymerize by more than one mechanism. Both thermodynamic and kinetic factors can be important, depending on the structure of the monomer and its electronic and steric situation. The initial step generates... 

Coatings emulsions are generally formed by addition polymerization of common, highly available monomers, using free radical initiators to create polymers having molecular weights from a few thousand up to millions. The polymerization is most often stabilized by non-ionic and/or anionic surfactants, which emulsify the insoluble monomer droplets, and then stabilize the resulting particles, usually in the shape of a sphere. In addition to surfactants, emulsions are sometimes stabilized with water-soluble poly-... 

Kinetics of Addition Polymerization. As the name suggests, addition polymerizations proceed by the addition of many monomer units to a single active center on the growing polymer chain. Though there are many types of active centers, and thus many types of addition polymerizations, such as anionic, cationic, and coordination polymerizations, the most common active center is a radical, usually formed at... 

Very high molecular weight polymers are formed by anionic polymerization of thiocarbonyl fluoride at low temperatures (58). These products are thioacetals that come about through addition polymerization of the 0=S bond. 

In addition to traditional radical initiated addition polymerizations, cation and/or anion catalyzed addition polymerizations are of great commercial importance, since PE, PP and PS are most frequently produced using this type of polymerization technique (Table 5). In addition to the vinyl monomers, vinyli-dene monomers, in which neither R nor R is hydrogen, can form commercially important polymers. PMMA is a typical example of this type of thermoplastics. 

Many homogeneous catalytic processes, in particular of anionic nature, are known, in which the polymerization takes place by stepwise addition (polymerization of ethylene oxide (34) of ethylene at low pressure and temperature with ALfia (7, 35), of styrene by Szwarc catalysts (36), for which the growth of the macromolecule can last for a very long time). This led some researchers to talk of a life of macromolecules and of living molecules (37). 

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