polymers 1

Question 1

what are polymers (basic, structurally)

Answer 1

organic materials containing carbon

Question 2

what is polymerisation?

Answer 2

joining up of many small molecules (mers/monomers), bonded together with strong covalent, intramolecular bonds, producing long, chain-like structures (or three dimensional structures

Question 3

why are polymers called macromolecules?

Answer 3

can be the order of 10^5-10^7 monomers making up a single polymer chain/network molecule, can treat one chain as a macromolecule

Question 4

draw diagram of linear, branched, crosslinked, and network molecular structures

Answer 4

nice!

Question 5

what is the ‘backbone’ of polymers often made of? (‘frame’ for network structures)

Answer 5

carbon

Question 6

draw a polymer chain with a carbon backbone and H side groups

Answer 6

go

Question 7

when are three dimensional polymer structures formed?

Answer 7

when there are more than two active bonding sites (see Phenol formaldehyde/Bakelite)

Question 8

what is a homopolymer vs a copolymer?

Answer 8

homopolymers: when all the repeating units are the same type
copolymers: polymers made from more than one type of monomer (see slide 7)

Question 9

what are the two mechanisms of polymerisation?

Answer 9

addition and condensation

Question 10

what are the stages of addition polymerisation?

Answer 10

1) initiation: R* + C2H4 -> RC2H4* where R* is the initial/radical electron. The double bond breaks (see slide 14)
2) growth: RC2H4* + C2H4 -> RC4H8*
3) termination: occurs either by meeting another growing chain or reacting with the initiator

Question 11

write an addition polymerisation reaction

Answer 11

see slide 15

Question 12

what is addition polymerisation?

Answer 12

polymer that forms by simple linking (addition) of monomers without generating byproducts

Question 13

what is condensation polymerisation?

Answer 13

requires reactive groups at the end of the monomer units. commonly water is given off in condensation reactions. slide 16

Question 14

what does the molecular weight of a polymer affect? and why?

Answer 14

properties eg melting/softening temperature. due to not all chains growing to be the same length, causes distribution of molecular lengths and thus weights. usually characterise polymers with their average weights

Question 15

what is the effect of molecular weight on the softening point?

Answer 15

as molecular weight increases, softening temperature increases. (eg @ room temp, short chain polymers are lliquid or gas. 1000 g/mol are waxy solids, and 10,000 g/mol or above are rigid solids)

Question 16

what is significant about the covalent bonds in polymers?

Answer 16

very very strong, and directional (ie angled at 109deg). backbone carbon atoms in a chain can lie anywhere on a cone with respect to their neighbours (slide 19)

Question 17

what are some different types of conformations?

Answer 17

formed due to bond rotation. can have twisted, coiled, or tangled conformations. end to end distance much smaller than actual chain length, good for large extensions of rubber materials

think how intestines are inside body, stretch out really long. bryony explained this well.

Question 18

why are mechanical/thermal properties affected by restriction of bond rotation?

Answer 18

chain segments’ ability to rotate in response to mechanical stresses or thermal vibrations. dependent on monomer structure. (double bonds give rigidity, as well as bulky side groups reduce chain mobility)

Question 19

why are additives used in plastics?

Answer 19

can increase strength, hardness, resilience, toughness, flexibility, stiffness. commonly serve multiple purposes, can use more than one additive

Question 20

examples of additives to polymers?

Answer 20

heat stabilisers, antioxidants, crosslinking agents, lubricants, flame retardants, colourants, UV absorbers, fillers

Question 21

why are fillers added to polymers?

Answer 21

to increase compressive and tensile strength, toughness, and hardness. synergistic effect is obtained, ie the mixture of filler and plastic gives better strength than the things on their own (eg wood flour + resin)

Question 22

examples of types of fillers?

Answer 22

wood flour (effectively a polymer. same density as phenol formaldehyde so remains low density).
silica flour (harder than wood flour, good with abrasion resistance, adds thermal stability but increase density)
fibrous fillers (good for adding strength to product)

Question 23

what are colourants?

Answer 23

change colour of polymer, may be added as dyes or pigments. dye - molecules dissolve and become part of polymer structure. pigments - do not dissolve and remain separate phase. usually prepared in masterbatch

Question 24

what are flame retardants?

Answer 24

interfere with the combustion process of the polymer, control gases present during combustion, or by initiation of chemical reactions which cool the combustion reaction

Question 25

what are plasticisers (additive)?

Answer 25

lower glass transition temperature of polymer, often used to decrease stiffness at room temp (increase flexibility or ‘softness’)