Addition polymers

Polymers are large molecules made from small molecules called monomers - for addition polymers the monomers are alkenes/substituted alkenes.

Conditions needed:

high temperature

high pressure

a catalyst

When alkenes form a polymer the double bond opens up to accommodate another monomer.

When ethene is polymerized, polyethylene (polythene) is formed – used for plastic bags and bottles. Notice that the polymer has no double bonds in the carbon backbone – it’s an alkane. The bonds are non-polar and strong – unreactive and difficult to break down, so can persist in the environment for a long time.

When naming the polymer, the word 'poly' is used as the prefix with the monomer enclosed in a bracket after it.

Polymer: poly(ethene)

Repeating Unit

Monomer

Poly(chloroethene)

Poly(chloroethene), also known as PVC (Polyvinyl Chloride), is a thermoplastic polymer that can be melted and remoulded multiple times without degradation.

PVC is commonly used in the construction industry for pipes, window frames, and siding due to its durability, resistance to water and chemicals, and low cost. It is also used in the manufacturing of vinyl flooring, electrical cables, and medical devices.

The properties of PVC can be modified by adding a plasticizer.- a substance added to a polymer to improve its flexibility and processability. When added to a polymer, plasticizer molecules are absorbed into the spaces between the polymer chains. In the case of PVC, the plasticizer molecule helps to break the intermolecular bonds between the polymer chains, reducing the attraction between the chains and increasing their mobility. This causes the material to become more flexible, softer, and less brittle. Plasticizers can also improve the processability of PVC by making it easier to extrude or mould into a desired shape. They are commonly added to PVC products such as vinyl flooring, shower curtains, and inflatable products.

The use of plasticizers in PVC has raised some concerns about their potential negative health effects, such as endocrine disruption. As a result, there has been a push towards the development and use of non-phthalate plasticizers, which are less harmful to human health and the environment.

Intermolecular Forces

Generally, addition polymers have nonpolar molecules and experience weak intermolecular forces due to the absence of functional groups that can form stronger intermolecular forces, such as hydrogen bonding or dipole-dipole interactions.

The dominant intermolecular forces between molecules of addition polymers are van der Waals forces, which include London dispersion forces and dipole-induced dipole interactions. London dispersion forces are the most significant intermolecular force in addition polymers, as they arise from the momentary fluctuations in electron density that occur in all molecules. The strength of these forces increases with the size and length of the polymer chains, making longer chains more cohesive and increasing their melting points.

In some cases, addition polymers can have small polar groups or functional groups that can contribute to intermolecular forces through dipole-dipole interactions. For example, polyvinyl chloride (PVC) contains a chlorine atom that creates a permanent dipole moment, which increases its intermolecular forces and makes it more cohesive than other addition polymers.