Vinyl Addition Polymerizations

Polymerization. Isoprene polymeri2ation can proceed by either 1,4- or l,2-(vinyl)addition (see Elastomers, synthetic-polyisoprene). 

Thermal Effects in Addition Polymerizations. Table 13.2 shows the heats of reaction (per mole of monomer reacted) and nominal values of the adiabatic temperature rise for complete polymerization. The point made by Table 13.2 is clear even though the calculated values for T dia should not be taken literally for the vinyl addition polymers. All of these pol5Tners have ceiling temperatures where polymerization stops. Some, like polyvinyl chloride, will dramatically decompose, but most will approach equilibrium between monomer and low-molecular-weight polymer. A controlled polymerization yielding high-molecular-weight pol)mier requires substantial removal of heat or operation at low conversions. Both approaches are used industrially. 

Vinyl copolymers contain mers from two or more vinyl monomers. Most common are random copolymers that are formed when the monomers polymerize simultaneously. They can be made by most polymerization mechanisms. Block copolymers are formed by reacting one monomer to completion and then replacing it with a different monomer that continues to add to the same polymer chain. The polymerization of a diblock copolymer stops at this point. Triblock and multiblock polymers continue the polymerization with additional monomer depletion and replenishment steps. The polymer chain must retain its ability to grow throughout the process. This is possible for a few polymerization mechanisms that give living polymers. 

Vinyl addition polymerizations, being chain reactions, are more complex than condensation polymerizations and they are generally more likely to include minor side reactions leading to branching or cross-linking. The structures of the pol3oneric products are consequently more difficult to establish with certainty. 

Substituted ethylenes in which substituents occur on both carbon atoms (with the exception of the fluoroethylenes) usually are not prone to polymerize, although some of them, such as the maleates and fumar-ates, copolymerize readily with other monomers. The further fact that, with rare exceptions, the monomers unite through the addition of the substituted carbon atom of one unit to the unsubstituted carbon atom of the next permits representation of nearly all vinyl addition polymers by the general structural formula... 

The difficulties of devising a basis for conveniently classifying various polymerizations in an appropriate manner have been discussed earlier in this chapter and several borderline examples which offer particular difficulty have been mentioned. One of these, the polymerization of the N-carboxyanhydrides, falls within the definition of a condensation polymerization, proceeds by a mechanism resembling a vinyl addition polymerization, and yields a product which possesses the structure of a typical condensation polymer. Definitions have been... 

As a consequence of facile homolytic cleavages, sulfonyl halides (I > Br > Cl F unsuitable) are able to add to unsaturated C—C systems. To prevent (or reduce) competing polymerizations, the additions of sulfonyl chlorides have been recommended to be carried out in the presence of copper(I/II) salts (Asscher-Vofsi reaction ). Comprehensive surveys have been published on the resulting j8-halogeno sulfones (or their vinyloguous compounds) as well as on their dehalogenation products (vinyl sulfones, 1-sulfonyl-l, 3-dienes, etc.). Table 5 reviews a series of sulfonyl halide additions and facile hydrogen halide eliminations. 

Photoinduced free radical graft copolymerization onto a polymer surface can be accomplished by several different techniques. The simplest method is to expose the polymer surface (P-RH) to UV light in the presence of a vinyl monomer (M). Alkyl radicals formed, e.g. due to main chain scission or other reactions at the polymer surface can then initiate graft polymerization by addition of monomer (Scheme 1). Homopolymer is also initiated (HRM-). 

The vinyl chloride monomer polymerizes via addition polymerization to form polyvinyl chloride. The final polymer has the chemical composition shown in Fig. 22.1. The polymer exhibits limited crystallinity, though this property is not often considered as important in defining its performance. It tends to be atactic or regionally syndiotactic, surrounded by extended atactic runs. When exposed to temperatures above 100 °C, polyvinyl chloride decomposes, creating free radicals that further attack the polymer chain, as we shall discuss in more detail later. For this reason, the degradation of polyvinyl chloride is autocatalytic... 

The standard gel-forming reaction is shown in Figure 8.2. Acrylamide and the cross-linker N, A-methylenebisacrylamide (bis) are mixed in aqueous solution and then copolymerized by means of a vinyl addition reaction initiated by free radicals.1317 Gel formation occurs as acrylamide monomer polymerizes into long chains cross-linked by bis molecules. The resultant interconnected meshwork of fiberlike structures has both solid and liquid components. It can be thought of as a mass of relatively rigid fibers that create a network of open spaces (the pores) all immersed in liquid (the buffer). The liquid in a gel maintains the gel s three-dimensional shape. Without the liquid, the gel would dry to a thin film. At the same time, the gel fibers retain the liquid and prevent it from flowing away. 

Identification by Methods of Chemical Probes 4.3.6.1 Initiation of Polymerization of Vinyl Additives... 

Now, the separation of polymers from the reaction mixtnre containing the vinyl additive indicates that the snbstrate prodnces a radical at the intermediate stage. The radical prodnced adds to a probe molecnle and forms an addnct with the vinyl monomer, that is, initiates the monomer polymerization. Sometimes, however, the polymerization does not start bnt the reaction yields a low-molecnlar-weight individnal snbstance containing fragments of substrate, an added monomer, and reactant. To illnstrate, let ns consider the following reaction of perfluoroalkyl iodide (snbstrate) with nitropropenide salt (reactant) in the presence of a monomer probe (vinyl acetate, methylmethacrylate, and styrene) (Feiring 1983) ... 

In fact, the first description of a polymeric vinyl ester dates back to 1912 when Klatte [1] managed to polymerise vinyl chloroacetate to obtain a solid resin. However, the potential of these materials was not seen at that time [2]. Additionally the polymerisation reaction faced severe practical problems leading to products... 

In general, there are two distinctively different classes of polymerization (a) addition or chain growth polymerization and (b) condensation or step growth polymerization. In the former, the polymers are synthesized by the addition of one unsaturated unit to another, resulting in the loss of multiple bonds. Some examples of addition polymers are (a) poly(ethylene), (b) poly(vinyl chloride), (c) poly(methyl methacrylate), and (d) poly(butadiene). The polymerization is initiated by a free radical, which is generated from one of several easily decomposed compounds. Examples of free radical initiators include (a) benzoyl peroxide, (b) di-tert-butyl peroxide, and (c) azobiisobutyronitrile. 

Figure 2.2 Polymerization of Cyclic Monomers (9-11). (RO) ROMP, (VA) Vinyl Addition Polymerization, (R/I) Radical/Ionic Polymerization...

In the vinyl addition polymerization, the bicyclic structural unit is left unchanged. Only the double bond is opened. The polymer obtained in this way does not contain double bonds. 

Poly(cycloalkene)s obtained from the vinyl addition polymerization method exhibit extremely high melting points. The high melting points make the polymers unprocessable. For this reason, comonomers, such as ethene or propene are introduced to lower the melting points. Copolymers of this type are addressed as COCs. 

F. Blank and C. Janiak, Metal catalysts for the vinyl/addition polymerization of norbomene, Coord. Chem. Rev., 253(7-8) 827-861, April 2009. 

Outside of vinyl addition polymerizations some crystallizable stereoregular polymers also have been prepared. An example is isotactic polymer from propylene oxide made by using ferric chloride com-... 

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