what is condensation polymer? please explain using Nylon and PET as examples.
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A condensation polymer is a type of polymer formed through a special reaction process. When monomers join together to form the polymer chain, they release small molecules like water, ammonia, or alcohol as byproducts. This is different from addition polymerization where monomers simply add together without losing any atoms. Common examples include nylon, PET, and even biological polymers like proteins and DNA.
Nylon is a classic example of a condensation polymer. It's formed from two types of monomers: a diamine like hexamethylenediamine, and a dicarboxylic acid like adipic acid. During the reaction, the amine group from one monomer reacts with the carboxylic acid group from the other monomer. This forms an amide linkage, and a water molecule is eliminated as a byproduct. The process repeats to create long polymer chains, resulting in the strong and flexible material we know as nylon.
PET, or polyethylene terephthalate, is another important condensation polymer. It's formed from ethylene glycol, which has two hydroxyl groups, and terephthalic acid, which has two carboxylic acid groups. During polymerization, the hydroxyl group from ethylene glycol reacts with the carboxylic acid group from terephthalic acid. This creates an ester linkage and releases water as a byproduct. PET is widely used in plastic bottles, food containers, and textile fibers due to its excellent chemical resistance and clarity.
It's important to understand the difference between condensation and addition polymerization. In condensation polymerization, like we saw with nylon and PET, a small molecule is eliminated during the reaction. This typically involves two different functional groups reacting together. In contrast, addition polymerization involves monomers with double bonds that simply open up and link together without any byproduct formation. Examples include polyethylene and PVC. The key distinction is that condensation involves an elimination reaction, while addition does not.
To summarize what we've learned about condensation polymers: They form through elimination reactions where small molecules are released as byproducts. Nylon is created from diamines and dicarboxylic acids forming amide linkages, while PET is made from diols and dicarboxylic acids forming ester linkages. This process is fundamentally different from addition polymerization, which produces no byproducts. Understanding these mechanisms helps us appreciate how different polymer structures and properties are achieved in materials science.