S2 Fulton L8-10 Flashcards
What is chain growth polymerisation
Monomers are added one at a time onto the end of the growing chain
What is step growth polymerisation
Chains grow in a stepwise process through reactions between functional groups in monomers
What was one of the first step growth polymers to be developed but what is the problem.
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
What is p in terms of step growth polymerisation
Extent of reaction (p) is a measure of the reaction conversion
What does it mean when p is 1
When p is 1, all acids/alcohols have reacted
What does it mean when p is 0
When p is 0 no acids/alcohols have reacted
What is the DP
Degree of polymerisation average number of monomers units in chain
How do we calculate the degree of polymerisation
DP = 1/(1-p)
What is needed to make high polymers
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
Describe the synthesis of nylon
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
Describe the synthesis of Kevlar
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.
Describe kevlar
The rigid nature of the inflexible polymer gives it fibres high strength (5 times stronger than steel) and polymer is heat resistant
What is the significance of nylon
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.
What are polyurethanes
Alternative to patent-protected nylon fibres. Relies upon the reaction of isocyanate with alcohol
What are the synthetic advantages of polyurethanes
There are no by-products to remove. There are hundreds of different types of polyurethanes depending on monomers used and methods of preparation
Describe Lycra
Lycra is an alternating block copolymer. Polyurea segmented provides elasticity. Lycra fibres are elastic and strong
What are polycarbonates
Polycarbonates are a group of thermoplastic polymers that contain carbonate groups (–O–(C=O)–O–) in their repeating molecular units.
Describe polycarbonates
Polycarbonates are strong, still, hard, tough, transparent engineering thermoplastics. They are optically clear
What is a dendrimers
Dendrimers are highly branched largely monodisperse macromolecules whose synthesis is stepwise in nature
What are the structure of dendrimers
Dendrimers have a core, branching unites and surface units
What is the generation number of the dendrimers determined by
The generation number is determined by the number of repeated branching cycles used in its synthesis
Define divergent synthesis of dendrimers
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)
What are the two high yielding and selective reactions used for divergent synthesis
Michael addition
Amidation
Describe what divergent synthesis needs after each step
Purifications are needed after each step to remove excess reagents
