Addition Polymers
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What is a polymer? (lrg. mol. - many rep. uni. - mon.)
A polymer is a very large molecule made up of many small repeating units called monomers
What type of monomers form addition polymers?
Monomers that contain a carbon - carbon double bond (alkenes)
Polymerise an ethene monomer, then name
Draw the proper structure/look at kerboodle and do your own and correct it - poly(ethene)
What is the repeat unit of a polymer?
The smallest group of atoms that repeats in the polymer chain
What are two main features of polymers (strong - prod. lng. chains - lrg. num. vdw - strong, C-C - strg. + non p. = chem. comp. can’t break = unrct.)
Strong because they produce long chains which then have large numbers of van der Waals forces which are very strong They also have carbon - carbon single bonds which are strong and non - polar, meaning few chemical compounds can break them, making them unreactive
What are plasticisers, and what role do they have in modifying plastics?
Plasticisers are small molecules that insert themselves between polymer chains, to force them apart and allow them to slide across each other
Why do polymers tend to have much higher melting points than the monomers that form them?
They are made up of long chains with many electrons that form very strong van der Waals forces and they cannot arrange themselves into a regularly lattice structure
With reference to intermolecular forces, suggest why all types of (x polymer) instead of
Why are polyalkenes not biodegradeable?
They have strong, non - polar C-C and C-H bonds in a saturated alkane backbone, making them unreactive and resistant to attack by biological agents (enzymes)
What kind of bonds make polyalkenes unreactive and non - biodegradable?
C-C and C-H bonds, which are non - polar and strong
How is low - density poly(ethene) (LDPE) made?
By polymerising ethene at high pressure and temperature via a free - radical mechanism
Why does low - density poly(ethene) have significant chain branching?
Free radical reactions are random, causing side branches to form
How does chain branching affect the properties of low - density poly(ethene)?
Branched chains pack poorly making them flexible, stretchy and have a lower density
How is high - density poly(ethene) (HDPE) made?
By polymerising ethene at low temperature and pressure using a Ziegler - Natta catalyst
Why does high - density poly(ethene) have a higher density than low - density poly(ethene)?
It has much less chain branching which allows the chains to pack more closely together
What effect does reduced branching have on high - density poly(ethene) melting point?
The melting point increases because tightly packed chains have stronger intermolecular forces
What is mechanical recycling?
A recycling method where plastics are sorted, washed, ground into pellets, then melted and remoulded into new products
What is feedstock recycling?
A process that involves plastics being heated to break their polymer bonds, converting into their monomers, so they can be reused to make new plastics
What is a key advantage of feedstock recycling over mechanical recycling?
Feedstock recycling can handle mixed or dirty plastics and produces monomers that are chemically identical to the original monomers
What is a limitation of feedstock recycling?
It can degrade the properties of plastics over time due to chain breakage during repeated heating