anionic and cationic polymerisation

what are the requirements of monomers for anionic polymerisation?4

EWG to stabilise anion by resonance

no acidic protons

no electrophilic groups

anion formed on monomer must react with another monomer

what are the two types of initiators in anionic polymerisation?

organometallic

radical anions from electron transfer

show how this makes anionic monomer

show how this makes anionic monomer

show how this makes radical anion?

what must be favourable for successful initiation?

free energy of initiation step must be favourable

how can the first addition be energetically favourable?

match the monomer with the right strength of initiator

what can you do if the propagating anion is not strongly stabilised?

powerful nucleophile needed as initiator

what solvents do you need for anionic polymerisation? give examples

solvents must be aprotic

e.g. saturated hydrocarbons - aromatic (benzene) or aliphatic (hexane)

why must solvents be dilute for anionic polymerisation?

how else must solvents be selected?

high conc polymers are often insoluble

to minimise chain transfer reactions

what temps are used for anionic polymerisation? why?

instability

low temps (-100 to +50C)

what happens if a protic solvent is used for anionic polymerisation?

show example with ammonia

can react with the active site

what is the significance of NH₂^-?

can initiate polymerisation of new chain

what is living polymerisation?

where a chain transfer or termination are absent

what are the 4 consequences of living polymerisation?

active, functionalisation, initation, synthesis?

chains are active indefinitely

chain end functionalisation can be carried out quantitatively

all chains initiated at similar time

synthesis highly controlled (molecular weight and distribution)

what is the conversion like for living polymerisation?

100%

what is the M_n proportional to in living polymerisation?

what is M_n controlled by?

directly prop to conversion

controlled by stoichiometry

what is the criteria for initiators of living polymerisation?

each initiator makes one chain

how are coblockpolymers made?

there is nothing for the anion to react with so there is no termination

• after first reacted, second monomer added etc

what is glass transition temperature (T_g)?

temperature at which amorphous materials transform form hard and brittle state into molten or rubber like state

what happens to chains at the glass transition temp?

molecular chains slide past each other when force applied

how do chemical groups affect T_g?

stiff groups (e.g. benzene) interfere with flowing process and increase T_g

if the glass transition temp of polybutadiene block is -90, and of polystyrene is +100, what happens between these temps?

what happens above T_g of styrene blocks? what does this mean about the material’s properties?

it behaves as a physically crosslinked elastomer

physical cross links change from rigid glassy regions to flowable melt regions

• flows and therefore can be cast, folded or extruded into desired form

what can be incorporated into a polymer to decrease T_g?

plasticisers

in cationic polymerisation, where do electrons come from?

what must monomers be like?

electrons come from monomer not initiator

monomers must be electron rich

show cationic polymerisation of this polymer

is cationic or anionic polymerisation faster?

cationic rates are faster

what temperatures is cationic polymerisation done at?

typically -40 to -80

to slow rxn down

are cations reactive or stable? what does this mean about polymerisation?

very reactive and hard to control and stabilise

more chain transfers and side reactions

how can nucleophiles affect cationic polymerisation?

react with cationic active centre and shut down polymerisation

what can be said about cationic polymerisation and dispersity? block copolymers?

it is difficult to make polymers with low dispersity

• tend to be different chain lengths

difficult to make block copolymers

which monomers can undergo cationic polymerisation?

stabilised by substitution (+I) or resonance (+M EDG)

what are the two types of initiators for cationic polymerisation?

protic acids

Lewis acids and cation source

show how HA acts as initiator for alkene monomer

which side of the alkene reacts?

reacts to form most stable cation (i.e. more substituted carbocation)

show example of lewis acid and cation source and how it makes a complex

how does this complex react with alkene monomer?

what are 3 suitable cation sources?

water

alcohols

ester

what are 3 suitable lewis acids?

SnCl₄

BF₃

TiCl₄

what can cationic polymers be terminated by?

counter ions

what is unimolecular rearrangement?

show with anion

anion acts as nucleophile

what is hydrogen abstraction?

show with anion

anion acting as base

why can this also be considered chain transfer?

HA is regenerated for initiation again

show example of chain transfer by hydrogen abstraction using alkene

cationic monomer regenerated

what are the properties of polyisobutylene?

high impermeability, chemical stability, flexibility and tackiness

what are the 3 applications of polyisobutylene?

rubber (gloves/tires)

fuel additives

chewing gum

why is polyisobutylene used as a fuel additive?

how is it functionalised?

forms hydrocarbon soluble backbone

polymer is functionalised with polar amine groups

keeps engines clean as absorbs carbonaceous deposits that build up on metal surface

how is gum made?3

gum base melted (polymer becomes flexible and malleable)

sweeteners and flavours added. mixing

scored and moved to temp controlled environment to cool

what is injection moulding?3

molten material/melted polymer is injected into mould

takes form of desired plastic item

solidifies on cooling to give plastic item