Conformation and Configuration of Polymer Molecules

The first task is to estimate the number of repeat units, n, in the polyethylene chain. Each repeat unit has 2 carbons and 4 hydrogen atoms. The molecular weight of carbon is 12 and that of hydrogen 1. Hence 

Using the diagram presented in Fig. 1.8 we can now estimate the length of the fully 

The conformation and configuration of the polymer molecules have a great influence on the properties of the polymer component. The conformation describes the preferential spatial positions of the atoms in a molecule. It is described by the polarity flexibility and regularity of the macromolecule. Typically, carbon atoms are tetravalent, which means that they are surrounded by four substituents in a symmetric tetrahedral geometry. The most common example is methane, CH4, schematically depicted in Fig. 1.9. As the figure demonstrates, the tetrahedral geometry sets the bond angle at 109.5°. 

This angle is maintained between carbon atoms on the backbone of a polymer molecule, as shown in Fig. 1.10. As shown in the figure, each individual axis in the carbon backbone is free to rotate. The configuration gives the information about the distribution and spatial organization of the molecule. 

Another type of geometric arrangement arises with polymers that have a double bond between carbon atoms. Double bonds restrict the rotation of the carbon atoms about the backbone axis. These polymers are sometimes referred to as geometric isomers. The X-groups may be on the same side (cis-) or on opposite sides (trans-) of the chain as schematically shown for polybutadiene in Fig. 1.12. The arrangement in a cis-1,4-polybutadiene results in a very elastic rubbery material, whereas the structure of the trans-1,4-polybutadiene results in a leathery and tough material. Branching of the polymer chains also influences the final structure, crystallinity and properties of the polymeric material. 

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