Condensation Polymers: Repeat Unit and Structural Units
In many condensation polymers the repeat unit contains two structural units related to the comonomers which have been polymerized. For example, in polyethylene terephthalate (PET or "polyester"), the repeat unit is -CO-C6H4-CO-O-CH2-CH2-O-. The polymer is formed by the condensation reaction of the two monomers terephthalic acid (HOOC-C6H4-COOH) and ethylene glycol (HO-CH2-CH2-OH), or their chemical derivatives. The condensation involves loss of water, as an H is lost from each HO- group in the glycol, and an OH from each HOOC- group in the acid. The two structural units in the polymer are then considered to be -CO-C6H4-CO- and -O-CH2-CH2-O-.
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