Chapter 3　Polymer Physics

3.1　Configurational States

The term configuration refers to the “permanent” stereo structure of a polymer. The configuration is defined by the polymerization method， and a polymer preserves its configuration until it reacts chemically. A change in configuration requires the rupture of chemical bonds. A polymer with the constitutional repeating unit —CH2—CHX—exhibits two different stere of configurational base units for each constitutional repeating unit（Figure 3.1）. The selected asymmetric carbon atom with the attached X atom（group of atoms） should be pointing upwards. The term d form is given to the arrangement with the X group pointing to the right（from the observer at the near end）. The I form is the mirror-image of the d form， i.e. the X group points in this case to the left. Different configurations exist in polymers with stereo centres（tacticity） and double bonds（cisandtransforms）. Tacticity is the orderliness of the succession of configurational base units in the main chain of a polymer molecule. Tacticity presents three forms of isotactic， syndiotactic and atactic. An isotactic polymer is a regular polymer consisting only of one species of configurational base unit， i.e. only the d or the I form（Figure 3.2）. A syndiotactic polymer consists of an alternating sequence of the different configurational base units， i.e .... dldldldldldl...（Figure 3.2）. An atactic polymer has equal numbers of randomly distributed configurational base units.

Figure 3.1　Configurational base units of a polymer with the constitutional repeating unit —CH2—CHX—. The X is an atom or a group of atoms different hydrogen

Figure 3.2　Regular tactic chains of CH2—CHX where X is indicated by a filled circle