S2 Fulton L8-10

Monomers are added one at a time onto the end of the growing chain

Chains grow in a stepwise process through reactions between functional groups in monomers

Polyesters as esterification was a very well understood reaction and there are many low molecular weight molecules available as building blocks. However ever the degree of polymerisation would never be much larger than 20 polymer molecular weight is too low to be useful for anything

Extent of reaction (p) is a measure of the reaction conversion

When p is 1, all acids/alcohols have reacted

When p is 0 no acids/alcohols have reacted

Degree of polymerisation average number of monomers units in chain

DP = 1/(1-p) where p is the extent of reaction

To produce polymers with a high DP, p must be very close to 1. To make high polymers the chemistry used to link together the monomers must be exceptionally efficient. Monomers also must be exceptionally pure

Nylon is a type of polyamide, made by step-growth polymerisation of a diamine and a dicarboxylic acid. Formation of a salt ensures a 1:1 ratio of monomers. Second step is melt polymerisation as temperature is above melting point of salt and polymer. Condensation occurs at high temperature to form amide. Water biproduct easily removed

The reaction of amines with acid chlorides is a good way to make Kevlar. Kevlar is made from this approach as the polymer cannot be melted.

The rigid nature of the inflexible polymer gives it fibres high strength (5 times stronger than steel) and polymer is heat resistant

Nylon shows that useful materials can be made that are based upon oil ( which is cheap and seemingly endless). Which is opposed to silk which is expensive and difficult to get a hold of as they were made from natural fibres.

Alternative to patent-protected nylon fibres. Relies upon the reaction of isocyanate with alcohol

There are no by-products to remove. There are hundreds of different types of polyurethanes depending on monomers used and methods of preparation

Lycra is an alternating block copolymer. Made up of polyurea and polyol. Polyurea segment provides hardness; polyol segment provides elasticity. Lycra fibres are elastic (can stretch 5 x) and strong.

Polycarbonates are a group of thermoplastic polymers that contain carbonate groups (–O–(C=O)–O–) in their repeating molecular units.

Polycarbonates are strong, still, hard, tough, transparent engineering thermoplastics. They are optically clear

Dendrimers are highly branched largely monodisperse macromolecules whose synthesis is stepwise in nature

Dendrimers have a core, branching unites and surface units

The generation number is determined by the number of repeated branching cycles used in its synthesis

Divergent approach refers to the way in which the dendrimers is induced to grow outwards from the core diverging into space (start at the core and build outwards)

Michael addition Amidation

Purifications are needed after each step to remove excess reagents