Materials- Polymers Intro Flashcards
Name some natural polymers
Wood, rubber, wool, leather, silk
Name some synthetic polymers
Plastics, some rubbers, fibre materials
What does polymer mean?
A class of macromolecule consisting of a set of regularly repeated chemical units of the same type, or possibly a very limited number of different types to form a chain molecule.
Describe how a polymer is arranged
Long, linear, thread-like molecules of variable length, composed of small definable molecular units, covalently bonded to one another to form a macromolecule.
Describe the molar mass of polymers
Large
Typically 10^4-10^6
What is ethylene also known as?
Ethene
Describe acetylene
Two carbon triple bonded together both attached to a H.
What is an unsaturated molecule?
A molecule that has double or triple covalent bonds. Each carbon is not bonded to four other atoms and it is possible for another atom or group of atoms to become attached to the original molecule.
What is a saturated molecule?
All bonds are single ones and no new atoms may be joined without the removal of others that are already bonded.
Structure of formaldehyde
Methanal
What is isomerism?
When compounds have the same composition but different atomic arrangements
Do physical properties depend on isomeric state?
Yes
What is a monomer?
The small molecule from which a polymer is synthesised
What is the angle between carbon atoms in a polymer?
109°
What is an isotactic polymer?
Where all of the monomers are joined in the same orientation. This makes the polymer more crystalline.
What is a syndiotactic polymer?
Where the monomers alternate between one orientation and the opposite orientation
What is an atactic polymer?
Where the orientation of the monomers in the chain is random
How does melting temperature change with molecular mass?
It increases for up to about 100,000g/mol
Typical molecular mass of liquid, waxy solid and solid polymers at room temperature
About 100 is liquid. About 1000 is waxy solid. Solid range from 10,000 and several million.
Graph of distribution for number of molecules with each molar mass after polymerisation.
Steep line up with ever-decreasing gradient. Then curves back down like exponential decay.
Formula for total mass of polymer
W=ΣNi
Where Ni is the total mass of each fraction which is number of moles of polymer with molar mass Mi
What are two sources of monomers?
Coal and crude oil
What is polymerisation?
The process where monomers are linked together to generate long chains composed of repeat units
What is the process for addition polymerisation?
Monomer units are attached one at a time to form a linear macromolecule. Has three stages of initiation, propagation and termination. Rapid process with molecule consisting of 1000 repeat units in the order 10^-2 to 10^-3 seconds
Initiation step of addition
There is an initiator with a free radical that attacks the monomer (with a C=C). The free radical moves onto carbon the initiator doesn’t join into because the double bond is broken. This carbon is the active centre of propagation.
Propagation step of addition
Linear growth of the polymer chain by the sequential addition of monomer units to this active growth chain molecule in the same mechanism as initiation step
Termination step of addition
Combination: the active ends of two propagating chains may link together to form one molecule.
Disproportionation: two growing molecules react to form two separate “dead chains”, one of which has a double bond at the end.
What is condensation polymerisation?
The formation of polymers by stepwise intermolecular chemical reactions that may involve more than one monomer species. There is usually a small molecular weight by-product such as water that is eliminated.
Generally longer reaction times than for addition.
For nylon classification, what does each number mean?
The first one is number of carbons between nitrogens. Second one is number of carbons between oxygens.
