Structure and Physical Properties of Polymers

In copolymers made of ethylene and vinyl acetate monomers, melting point and degree of crysfallinify decrease as the percentage of vinyl acetate increases. Suggest an explanation. 

The simple structural formulas given for polyethylene and other polymers are deceptive. Because four bonds surround each carbon atom in polyethylene, the atoms are arranged in a tetrahedral fashion, so that the chain is not straight as we have depicted it. Furthermore, the atoms are relatively free to rotate around the C—C single bonds. Rather than 

In copolymers made of ethylene and vinyl acetate monomers, melting point and 

Polymers can be made stiffer by introducing chemical bonds between chains. Forming bonds between chains is called cross-linking ( FIGURE 12.41). The greater the number of cross-links, the more rigid the polymer. Whereas thermoplastic materials consist of independent polymer chains, thermosetting ones become cross-hnked when heated the cross-links allow them to hold their shapes. 

A FIGURE 12.39 Asegmentof a polyethylene chain. This segment consists of 28 cai1x n atoms. In commercial polyethylenes, the chain lengths range from about 10 to to CH2 units. 

A FIGURE 12.41 Cross-linking of polymer chains. The cross-linking groups (red) constrain the relative motions of the polymer chains, making the materiai harder and less flexible than when the cross-links are not present. 

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As polymer scientists continue to investigate the atomic structure and physical properties of polymers, the need for more accurate models to describe various experi-... 

Askadskii AA and Matvyeyev Yu I, "Khimicheskoye Stroyeniye i Fizicheskiye Svoistva Polimerov" (Chemical Structure and Physical Properties of Polymers). Nauka, Moskva, 1983. 

Askadsky A.A., Matveev U.I. Chemical a structure and physical properties of polymers.-M. Chemistry.-1983.-248 p. 

A.A. Askadskii, Yu.1. Matveev, Chemical structure and physical properties of polymers. Chemistry, Moscow, 1983. 

Investigation of the relationship between the structure and physical properties of polymers is one of the most important themes for polymer chemists and engineers. Polymer structures have been determined through many types of spectroscopy. Nuclear magnetic resonance (NMR) is now an indispensable tool for analyzing polymer structures [1-3]. 

Since PRISM theory accounts for density fluctuations, it can be used to calculate of local structure and physical properties of polymer liquids. This is not possible, for example, in self-consistent field theory [2] where density fluctuations are neglected due to the incompressibility assumption. 

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