Polymers Polymerisation - Methods of sticking Mers together The process of sticking mers together is called polymerisation. The two ways of doing this are; 1- Additional polymerisation, this is the most important of the two because most important polymers are made this way and, 2- Condensation polymerisation. This method tends to yield rigid plastics.

Polymers Addition Polymerisation The basic idea of sticking mers together like this is similar to a zip. The mers are added onto the end of a growing chain. There are three basic parts to the process: Initiation - Polyethylene C2H4, has a double bond between the carbon atoms. One of these bonds is stronger, while the other is weak. Each bond contains two electrons. The weak bond is attacked by a radical.

Polymers Addition Polymerisation This radical grabs an electron and leaves one electron behind. Propagation -When other ethylene molecules come near the ethylene radical they too are attacked and a mer is attached. The combined molecule is a growing chain radical. The process continues by adding other ethylene molecules in a similar fashion.

Polymers Addition Polymerisation Termination - Possible stops to the growing chains could simply be running out of mers or radicals.

Polymers Condensation Polymerisation This process depends on splicing rather than zipping. The starting molecules are spliced or joined together with small molecules, like water, being condensed out of the reaction at the end of polymerisation. The remaining structure is a comples 3D structure which is rigid and has a significant cross-linking feature.

Polymers Condensation Polymerisation H C = O . Formaldehyde OH Phenol OH OH H C +H2O

Polymers Types of Polymers Thermoplastics: These are thermosoftening polymers and make up about 85 - 90% of the bulk of polymers. They include; High Density Polyethylene --HDPE Low Density Polyethylene --LDPE Poly Vinyl Chloride --PVC Polystyrene -- PS Polypropylene -- PP

Polymers Types of Polymers Thermosetting: The important ones in this group include; Phenolics - This is a group of polymers based on phenol formaldehyde (PF) the original developed by bakeland. It is a cheap, brittle, muddy-brown (or black or blue) polymer. Urea-formaldehyde - A white polymer that can be easily coloured. Uses include electric plugs, sockets, and other fittings.

Polymers Types of Polymers Melamine-formaldehyde. This is harder, more scratch resistant and clearer. It can be found in ‘melaware’ and formica table tops Polyesters - This is the resin used in fibreglass production. Epoxies - This polymer is used in adhesives. Polyurethanes - Are hard to classify as they can exist as hard glassy polymer or as a soft flexible sponge.

Polymers Additives for Polymers Just as metals are alloyed to improve their properties, substances are added to polymers to improve theirs. A typical example is