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Discusses the synthesis of industrial polymers and the principles of sustainable chemical design.
What if the very materials that built our modern world—from the phone in your pocket to the clothes on your back—could be redesigned to disappear without a trace once their job is done?
In addition polymerization, unsaturated monomers (containing double or triple bonds) link together without the loss of any atoms. This process typically involves three stages: initiation (using a free radical), propagation (the chain grows), and termination. A classic example is the production of polyethylene from ethene monomers (). Because no atoms are discarded, the atom economy of addition polymerization is theoretically . These polymers are often chemically inert and non-biodegradable, leading to significant environmental challenges.
1. Start with ethene monomers: . 2. Apply heat and a catalyst to break the -bond. 3. The monomers link to form a long saturated chain: . 4. This polymer is used for plastic bags and bottles due to its flexibility and strength.
Quick Check
Why does addition polymerization typically result in a 100% atom economy?
Answer
Because all atoms present in the monomers are incorporated into the final polymer chain with no byproducts created.
Unlike addition reactions, condensation polymerization involves monomers with two different functional groups. When these monomers react, they form a bond and release a small molecule, usually water () or hydrogen chloride (). Common examples include polyesters (formed from diols and dicarboxylic acids) and polyamides like Nylon-6,6 (formed from diamines and dicarboxylic acids). Because a byproduct is lost, the mass of the polymer is always less than the total mass of the starting monomers.
1. React a dicarboxylic acid: . 2. Add a diol: . 3. The from the acid and the from the alcohol combine to form . 4. An ester link () connects the monomers into a chain: .
Quick Check
What is the primary structural difference between the monomers used in addition vs. condensation polymerization?
Answer
Addition monomers require a carbon-carbon double bond (unsaturation), while condensation monomers require two reactive functional groups (like -OH, -COOH, or -NH2).
Industrial chemistry is shifting toward Green Chemistry, a framework of 12 principles designed to reduce environmental impact. Key principles include Atom Economy, which measures how much of the reactants end up in the product, and the use of Renewable Feedstocks. In polymer science, this means moving away from petroleum-based monomers toward plant-based alternatives (like PLA from corn starch) and designing polymers that are biodegradable to prevent long-term pollution.
Which polymer is formed through an addition reaction?
In the synthesis of a polyamide, which small molecule is most commonly released?
A reaction with high atom economy is always considered 'green' regardless of the toxicity of the reagents.
Review Tomorrow
In 24 hours, try to sketch the difference between an ester link and an amide link from memory.
Practice Activity
Look at the recycling symbols on plastic items in your home. Research whether they are made via addition or condensation polymerization.