Addition/condensation polymers (as required)

Imagine you have lots of identical LEGO bricks. If you click them all together in a long line, you've made a long chain! In chemistry, these tiny individual LEGO bricks are called monomers (mono means one). When many, many monomers join together, they form a giant, long chain called a polymer (poly means many).

There are two main ways these monomers can link up to form polymers:

• Addition Polymerization: Think of this like linking hands in a long chain. Each person (monomer) just adds on to the next without anything else being lost. It's like a simple chain reaction where nothing is wasted.
• Condensation Polymerization: This is a bit different. Imagine two people (monomers) want to join hands, but first, they have to drop a small item, like a tiny pebble (a small molecule like water), before they can link up. So, when they join, a small molecule is 'condensed' out or removed.

Let's think about how a simple plastic bag, made of poly(ethene), is created. This is a perfect example of addition polymerization.

1. The Monomer: The starting LEGO brick is a small molecule called ethene. Ethene has a special 'double bond' between its carbon atoms, which makes it very reactive, like having two sticky hands ready to grab onto something.
2. The Joining Process: When you heat ethene under high pressure and add a special chemical helper (a catalyst), those double bonds 'break open'. Imagine the two sticky hands opening up.
3. The Chain Forms: Once the double bond opens, each ethene molecule can then link up with another ethene molecule, and then another, and another! They just keep adding on, one after the other, forming a super long chain. Nothing else is produced, just the long poly(ethene) chain.
4. The Polymer: This long chain is poly(ethene), which we commonly call polythene. It's what makes plastic bags, milk bottles, and many other plastic items.

This type of polymerization is like a continuous adding machine. It only works with monomers that have a carbon-carbon double bond (C=C), which is like their 'sticky part'.

1. Monomer Activation: The double bond in the monomer (like ethene) 'opens up' or breaks, making the carbon atoms ready to form new bonds. Think of it as unzipping a zipper.
2. Chain Initiation: A special starter molecule (often from a catalyst) attaches to one of these opened-up monomers, beginning the chain.
3. Chain Propagation: This 'activated' monomer then bumps into another monomer, and its opened bond links to the next monomer's opened bond. The chain grows longer and longer, adding one monomer at a time.
4. Chain Termination: Eventually, two growing chains might meet, or the chain might run out of monomers, and the reaction stops. The result is a very long polymer chain.
5. No By-products: The cool thing about addition polymerization is that nothing else is formed. All the atoms from the monomers just rearrange into the single, long polymer chain. It's a very efficient way to build!