Question

Which of the following are example of addition polymerisation? (a) Hexamethylene + Adipic acid \(\rightarrow\) Hexamethylene diamine (b) Ethylene glycol + Terephthalic acid \(\rightarrow\) Dacron (c) Styrene \(\rightarrow\) Polystyrene (d) None of the above

Short answer

The answer is (c). Only the polymerisation of styrene to produce polystyrene represents an example of addition polymerisation.

Step-by-step solution

Check Reaction (a)

Examine the reaction Hexamethylene + Adipic acid \(\rightarrow\) Hexamethylene diamine. This reaction is a condensation polymerisation and not an addition polymerisation because it involves the loss of water molecules during the reaction. Hence, it does not fit the criteria.

Check Reaction (b)

Examine the reaction Ethylene glycol + Terephthalic acid \(\rightarrow\) Dacron. This is another example of condensation polymerisation because it leads to the loss of water molecules during the reaction. Hence, it isn't an example of addition polymerisation.

Check Reaction (c)

Examine the reaction Styrene \(\rightarrow\) Polystyrene. This is an example of addition polymerisation because styrene molecules (monomers) are joined together without the loss of any material or molecule.---the double bond in the styrene molecule is broken allowing the molecules to join together. Hence, it fits the criteria.

Key concepts

Condensation Polymerisation

Understanding the concept of condensation polymerisation is essential when distinguishing it from addition polymerisation. In condensation polymerisation, two different monomers come together and react in such a way that a small molecule, often water, is eliminated. This process repeats, linking monomers and 'condensing' out water or other small molecules, forming a long chain or network polymer. Typical examples involve monomers with functional groups like acids, amines, or alcohols.

For example, when hexamethylene and adipic acid react, they form hexamethylene diamine and release water in the process. Similarly, ethylene glycol and terephthalic acid react to produce Dacron, also releasing water. These reactions are typical condensation reactions because of this loss of water. The process is step-growth, meaning that dimers form first, then trimers and so on until high molecular weight polymers are produced.

In the context of a classroom or homework exercise, it's vital to identify the presence of functional groups that can facilitate the condensation process, and to look for the byproducts that are characteristic of this type of polymerization.

Polymer Chemistry

Polymer chemistry is the study of large, complex molecules composed of repeated subunits called monomers. We have two primary classifications in polymer chemistry: addition polymerisation and condensation polymerisation, each with distinct mechanisms and characteristics. Addition polymerisation involves monomers with unsaturated bonds, such as double or triple bonds, where these reactive sites link together without producing a byproduct.

An exemplar of addition polymerisation is the transformation of styrene to polystyrene. Here, the double bonds in the styrene monomer break and form new bonds with adjacent monomer molecules, creating a long and repeating chain structure. There's no loss of atoms; all atoms in the monomers are retained in the final polymer structure, which is a defining hallmark of addition polymerisation.

In classroom settings or homestudy, identifying polymerisation types is crucial. For example, spotting unsaturated monomers can provide a hint that the reaction is likely to be an addition polymerisation, especially when no small molecules are eliminated.

Monomer Reactions

Monomer reactions are the fundamental chemical reactions where monomers, the building blocks of polymers, link together to form larger molecules. In addition polymerisation, monomers react in a way that preserves all their atoms in the final polymer. This differentiates addition from condensation polymerisation, where some atoms are expelled as small byproduct molecules. Monomer reactions are influenced by various factors, including temperature, catalysts, and the nature of the monomers themselves.

Styrene, for example, undergoes addition polymerisation to become polystyrene. The reaction takes advantage of the double bond in styrene, which allows for the monomers to attach to each other one by one, as they open up their double bonds and link up in a 'chain-growth' polymerisation fashion. Recognizing the type of monomer involved in a reaction is critical when predicting the polymer that will be produced. In academic exercises, you should assess the monomer's structure and determine whether an addition or condensation mechanism is at play.