Configuration of polymers

Configuration describes how the repeating units are oriented in relation to one another. This was set during polymerization. Tacticity is one such parameter. Non-symmetrical repeating units, such as the Propene in Figure 2 can have its substituent, here the methyl group, oriented in different positions. This makes each carbon atom of the polymer with the substituent a chiral centre.

As illustrated in Figure 3 the stretched out polymer has its substituent pointing in either the same direction, which is isotactic configuration or in alternating directions which is called syndiotactic. If the substituent is randomly orientated the polymer is called atactic. Some polymers are also prone to arrange themselves with its substituent on adjacent carbons. This causes a head-to-head coupling.

Task: Contemplate on the tacticity options for polyethylene, PE, with repeating unit: -[CH2-CH2]n-.

Check answer

syndiotactic Polypropylene

Figure 3. Illustration of syndiotactic Polypropylene, top, and isotactic Polypropylene, bottom
© Anders Persson, University of Borås

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