Polymers Flashcards
What are polymers?
Polymers are very large molecules that consist of thousands of small repetitive units (called monomers) linked by covalent bonds
What is the polymer structure?
covalent molecular substances composed of many small molecules joined together to forma long chain of atoms.
What are some examples of natural polymers?
proteins, starch, cellulose and DNA
What is an example of a synthetic polymer?
Bakelite
hard, brittle plastic used to make cases for items like telephones and electrical guitars
As polymer chain get longer…
the strength of the dispersion forces between neighbouring polymer chains increases.
The stronger the dispersion forces….
the harder and more rigid material of a polymer
What are the two different types of branching of polymer chains?
Linear fashion or with a degree of branching
What are branched polymers?
are formed when some monomers react with sites on the side of the polymer chain instead of the ends.
What straight chain polymer?
When monomer joins to the side of the polymer chain, it begins a new chain growing a different direction.
How does branching affect properties of polymers?
Branching can cause polymer molecules to be spaced further apart, resulting in less dense materials
The greater distance between the polymer chains
the intermolecular attraction between neighbouring chains is weakened, increasing flexibility of material.
What are the bonds between thermoplastic polymers?
bonds between long polymer chains are hydrogen, dipole-dipole bonds or weak dispersion forces, rather than covalent bonds.
Why are thermoplastic polymers soft when they are heated and can be remoulded and recycled?
when heated molecules in thermoplastic materials have enough energy to overcome intermolecular forces and become free to move and slip past one another.
When can straight chain and branched chain polymers exist as thermoplastic polymers?
as long as there are no covalent cross-links between polymers chains.
What are cross-linked polymers?
polymer branches are covalently bonded to neighbouring polymer chains
Why can’t cross-linked polymers become liquids?
bonding creates a polymer network, polymers like this cannot be liquids because of polymer chains are held inlace by cross-linking and are unable to flow.
What are thermosetting polymers?
thermosetting polymers decompose or burn when heated, rather than melting and are hard and rigid.
Why are cross-linked polymers usually thermosetting polymers? and why don’t they melt?
do not soften as bonds between chains are very strong therefore a high temp must be used to break the bonds, causing the polymer to decompose.
Why cant thermosetting polymers be recycled?
it is difficult to recycle thermosetting polymers as they cannot be remoulded into new shapes
How are elastomers formed?
when occasional cross-links are presents.
As chains move past each there when stretched, but cross-links return the chains to their original position once the foresee causing stretching is released.
What happens when elastomers are heated?
crosslinks stop them from completely melting when heated and makes recycling difficult.
What are low density polyethene?
eg. cling wrap
they are longer and frequent keeping chains further making it less dense.
What are high density polyethene?
eg. bottles
there arent a large number of branches so they pack together tightly, increasing the density and hardness of the polymer formed.
How does additional polymerisation occur?
Double bonds are broken and new covalent bonds are formed between carbon atoms on nearby monomers. Only unsaturated monomers.