Linear vinyl polymers

In spite of the fact that asymmetric carbon atoms1 are formed in the synthesis of vinyl polymers, head-to-tail linear vinyl polymers showing remarkable optical activity in solution cannot be prepared by the usual polymerization processes unless asymmetry centers are already present in the monomers (6, 13). In fact, by considering the principal types of vinyl polymers prepared up to now, the ideal isotactic macromolecules, having such terminal groups as to render both terminal segments of the macromolecule chemically identical, possess a symmetry plane and therefore the polymers cannot show optical activity they might be considered as a peculiar type of meso compounds. 

Most of the imprinted polymers described to date are copolymers, i.e. polymers formed by incorporating two monomers in the polymer. Depending on the relative reactivity of the monomers different types of polymers are formed [10]. For linear vinyl polymers these are ... 

Preparation of Optically Active Linear Vinyl Polymers by Templated Synthesis... 

Resin and Polymer Solvent. Dimethylacetamide is an exceUent solvent for synthetic and natural resins. It readily dissolves vinyl polymers, acrylates, ceUulose derivatives, styrene polymers, and linear polyesters. Because of its high polarity, DMAC has been found particularly useful as a solvent for polyacrylonitrile, its copolymers, and interpolymers. Copolymers containing at least 85% acrylonitrile dissolve ia DMAC to form solutions suitable for the production of films and yams (9). DMAC is reportedly an exceUent solvent for the copolymers of acrylonitrile and vinyl formate (10), vinylpyridine (11), or aUyl glycidyl ether (12). 

Plasticizers. Plasticizers are materials that soften and flexibilize inherently rigid, and even britde polymers. Organic esters are widely used as plasticizers in polymers (97,98). These esters include the benzoats, phthalates, terephthalates, and trimeUitates, and aUphatic dibasic acid esters. Eor example, triethylene glycol bis(2-ethylbutyrate) [95-08-9] is a plasticizer for poly(vinyl butyral) [63148-65-2] which is used in laminated safety glass (see Vinyl POLYMERS, poly(vinyl acetals)). Di(2-ethyUiexyl)phthalate [117-81-7] (DOP) is a preeminent plasticizer. Variation of acid and/or alcohol component(s) modifies the efficacy of the resultant ester as a plasticizer. In phthalate plasticizers, molecular sizes of the alcohol moiety can be varied from methyl to tridecyl to control permanence, compatibiUty, and efficiency branched (eg, 2-ethylhexyl, isodecyl) for rapid absorption and fusion linear (C6—Cll) for low temperature flexibiUty and low volatility and aromatic (benzyl) for solvating. Terephthalates are recognized for their migration resistance, and trimeUitates for their low volatility in plasticizer appHcations. 

The simplest linear-chain polymer is polyethylene (Fig. 22.3a). By replacing one H atom of the monomer by a side-group or radical R (sausages on Fig. 22.3b, c, d) we obtain the vinyl group of polymers R = Cl gives polyvinyl chloride R = CIT3 gives... 

Poly(vinyl fluonde) is a linear semicrystalhne polymer of the following general structure... 

Stoicescu and Dimonie103 studied the polymerization of 2-vinylfuran with iodine in methylene chloride between 20 and 50 °C. The time-conversion curves were not analysed for internal orders but external orders with respect to catalyst and monomer were both unity. Together with an overall activation energy of 2.5 kcal/mole for the polymerization process, these were the only data obtained. Observations about the low DP s of the products, their dark colour, their lack of bound iodine and the presence of furan rings in the oligomers, inferred by infrared spectra (not reported), completed the experimental evidence. The authors proposed a linear, vinylic structure for the polymer, and a true cationic mechanism for its formation and discussed the occurrence of an initial charge-transfer complex on the... 

Hyperbranched polymers are generally composed of branched (dendritic), Hn-ear, and terminal units. In contrast to AB2 systems, there are two different types of linear units in SCVP one resembles a repeat unit of a polycondensate (----A -b----) and one a monomer unit of a vinyl polymer (--a(B )---). 

FIGURE 2.13 Helical conformation of isotactic vinyl polymers. (From Gaylord, N., Linear and Stero-regular Addition Polymers, Wiley, New York, 1959. With permission.)... 

Natta, a consultant for the Montecatini company of Milan, Italy, applied the Zeigler catalysts to other vinyl monomers such as propylene and found that the polymers were of higher density, higher melting, and more linear than those produced by the then classical techniques such as free-radical-initiated polymerization. Ziegler and Natta shared the Nobel Prize in 1963 for their efforts in the production of vinyl polymers using what we know today as solid state stereoregulating catalysts. 

Three types of stationary phases based on the free-radical reaction of monocationic and dicationic vinyl-substituted imidazolium cations were studied [42]. Two examples of such monomers are given by ILs 9 and 10 in Table 4.1. The formation of a linear IL polymer stationary phase was performed by the free radical polymerizafion of monocationic monomers. 

The photo-cross-linkability of a polymer depends not only on its chemical structure, but also on its molecular weight and the ordering of the polymer segments. Vinyl polymers, such as PE, PP, polystyrene, polyacrylates, and PVC, predominantly cross-link, whereas vinylidene polymers (polyisobutylene, poly-2-methylstyrene, polymethacrylates, and poly vinylidene chloride) tend to degrade. Likewise, polymers formed from diene monomers and linear condensation products, such as polyesters and polyamides, cross-link easily, whereas cellulose and cellulose derivatives degrade easily. ... 

Furthermore, microstructural variations of cis, trans, and vinyl contents have no discernible effect on the relation between g and g" of Figures 3-5. Since the same linear butyllithium polymers containing 10% vinyl isomer were used as reference in calculating g and g", it is likely that microstructural differences have been cancelled. 

Obviously, the polymerization of ethylene does not involve isotactic steric control, since no isomers are possible in the linear polyethylene polymer. However, as the simpliest member of the vinyl monomer series, ethylene should be considered along with the substituted ethylenes. Where does the Ziegler catalyst, which produces polyethylene, lie in relation to the polypropylene catalysts ... 

The atactic polymers, as well as the linear head-to-tail vinyl polymers consisting of macromolecules having different terminal groups, obtained by the known polymerization processes, are in general optically inactive owing to intramolecular compensation. 

The macromolecules of optically active linear head-to-tail vinyl polymers contain asymmetric carbon atoms both in the principal and in the lateral chains. However, as the asymmetric carbon atoms in the principal chain cannot give a high contribution to the rotatory power (7), the optical activity of the known vinyl polymer is mainly related to the presence of asymmetric carbon atoms in the lateral chains. 

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