polymers haddleton

Radical polymerisation using chain transfer, what does this mean

radical polymerisation is one active chain grows rapidly by adding monomers one at a time.

diff types are radical

cationoc

anionic

coordination (zieglar natta) we gonna focus on radical

so what are the main steps of radical polymerisation

initiation

propagation

termination OR

chain transfer

What is the advantage of chain transfer here

chain transfer instead of having

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u get

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This is beneficial overall because u get lots of few chains rather than large chains, which decreases molecular weight, creates more polymer chains, lowers degree of polymerisation.

Equations for each and their rate

Intitiaon

propagation

termination

Initiation:

Initiation →2R°

R° + {monomer} →RM°

Rate:K₁[M][R°]

Propagation

[RM°] + [M] → [RMM°]

Rate=Kp [RM°][M]

Termination

Pol° + pol° → Polymer

Rate= Ktc[Pol*]² +Ktd[Pol*]²

Termination can be disproportion or combination.

combination is 2 monomers with radical at the end joining to become one. no radical left.

disproportion is when dead chain + dead chain, by stealing hydrogen from another.

this is extra intel. how does a monomer know to terminate by combo or disproprtion

Bulky steric hinderance and high temp usually go for stealing H, so disproportion.

what is an example of chain transfer

in chain transfer a new radical is born

P• + X-H → P-H + X•

then X becomes radical

what is cctp aka batch

catalytic chain transfer polymerisation. uses a catalyst to promote chain transfer, producing low-molecular-weight polymers and macromonomers.deliberately make chains stop growing early via chain transfer.

Whats CCTP mechanism

Use Cobalt 2+ as the catalyst here. starting from green.

add the growing chain radical then the carbon becomes sterically hindered. becomes co 3+. leaves by sn2 i think reaction.

cobalt hydride left which is unstable initiates the next chain

makes co2+ again

Give me an overview on living radical polymerisation

living polymerisation is a type of radical polymer. it chains reversibly switch between active and dormant states, greatly reducing termination and allowing precise control over molecular weight, dispersity, and polymer architecture.

Ok so what is RAFT

RAFT is a type of living polymerisation. it is reversible addition fragment transfer

what is happening in each step

RAFT Mechanism

1. Initiation

Initiator → 2R•

R• + M → RM•

RM• + M → RMM•

RMM• + M → RMMM•

(Growing polymer radical forms)

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2. Addition

Mn• + Z-C(=S)-S-R

↓

Mn-S-C•(Z)-S-R

(Growing radical adds to the RAFT agent)

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3. Fragmentation

Mn-S-C•(Z)-S-R

↓

Mn-S-C(=S)-Z + R•

(The original polymer chain becomes dormant and a new radical is released)

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4. Re-initiation

R• + M → RM•

RM• + M → RMM•

(New polymer chain begins growing)

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5. Equilibration

Mm• + Mn-S-C(=S)-Z

↓

Mm-S-C•(Z)-S-Mn

↓

Mm-S-C(=S)-Z + Mn•

(Radical activity is transferred from one chain to another)

--------------------------------------------------

6. Reversible Exchange

Chain A active → Chain A dormant
Chain B dormant → Chain B active

Chain B active → Chain B dormant
Chain C dormant → Chain C active

Chain C active → Chain C dormant
Chain D dormant → Chain D active

(The radical is continually passed between chains)

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Outcome

ACTIVE ⇌ DORMANT

Only a small number of radicals exist at any time.

↓

Less radical-radical termination

↓

More uniform chain growth

↓

Controlled molecular weight

↓

Low dispersity

↓

Block copolymers can be formed

on a paper write out raft in chemical equation terms. using Pm* as initiation monomer

what are three main suitable RAFT agents

Dithiobenzoates

trithiocarbonates

dithiocarbamates

Dp equation for raft

DP=[Monomer]/[Raft]

need a constant supply of radicals

always some polymer with twice the target MWt due to combination

Why does reversible homolytic dissociation lead to living radical polymerisation

The growing polymer radical reversibly forms a dormant covalent adduct. Since only a very small concentration of radicals is present at any time, termination reactions are greatly reduced, allowing controlled growth of polymer chains and narrow molecular weight distributions

write out a covalent adduct formula and what is it

L—>←—[R* T] —>←- R* +T*

BASICALly, T here depending on what method can be nitrogen (nmp) or copper complex.

What it shows is two chains joined together by covalent bond important because R* can terminate. But R*-nitrox cannot, its like a lid on top

what is aloxyamine

when heated molecule breaks off to become TEMPO and a reactive radical

whats special about tempo

Tempo is a stable radical, because lots of steric hinderance lots of bulky group preventing it from bonding to another radical so it can exist as tempo* for a long time. Then

polymer*+M→ polymer-M*

polymer-M* +Tempo*→ polymer Mtempo becomes dormant this usually works with reasonably stable monomers such as styrene, acrylates no catalyst required. Raft usually has sulphur catalyst

how would a bimolecular compound like this react with TEMPO

unimolecular and TEMPO

draw out initiation , prop and reverersible termination with this

whats this equation showing Mn= Mo x [M]/[I]

Mn is number average molecular weight, so tells u how big a polymer is like 100 chains etc

and Mo of one repeat unit, so styrene being 104 gmol-1

DP= M/I. degree of polymerisation. How many monomers joined together in one chain. so styrene x 4. DP=4

Styrene is polymerised by living radical polymerisation.

Given:

• Molecular weight of styrene = 104 g mol⁻¹

• Initial monomer concentration = 0.50 mol

• Initiator concentration = 0.010 mol

Calculate the theoretical Mn

DP= 0.5/0.01

=50

Mn= 50× 104

=5200g mol

nitroxide mediated copolymerisation out of acrylate, methacrylate and styrene. Is bad for which one

works well with styrene, not much acrylates because side reactions start occuring

Whats the concept of ATRP

atom transfer radical polymerisation. A halogen atom (br/cl) keeps hopping on and off the polymer chain instead of nitrogen

p*

p-br

p-br →← P*

This uses a metal catalyst so sometimes uses cu(ii) to cu(iii)

what essentiall is happening between these two pics

Top one is cationic, lewis acid being alcl3 or BF3, breaks the C-X bond heterolytically, meaning both electron goes to one atom, so ions form. active species is a polymer+, a carbocation

Bottom one, basically atrp, but the difference is it uses metal catalyst Cu(I) and breaks homolytically. c-x → polymer* and X-cu (II).

basically both system use the same active dormant technique but in different ways,

Pn-X + Mtn/L for this how would you expect initiation to go

Pn* + X-Mtn+1/L

sometimes the metals are binded to a ligand for example

Cu (i)TMEDA, why?

to stabilise the metal, and tune its reactivity

why is ATRP considered living

because p* conc is low and termination is also kept low. Mn increases with conversion

Why must initiation be faster than propagation in living polymerisation

So all polymer chains start growing at approximately the same time, leading to uniform chain lengths and low dispersity.

how do we make atrp initiators from alcohols

alcohol+ aklkyl halogen→atrp ester

an example being 2 bromoisobutyryl bromide

its to show that atrp can occur from wide range of molecules

why is this reaction important

the product is a schiff base, its a ligand that attaches itself to the transition metal in atrp reactions

what can be inferred from the diagram and its R group

Changing the ligand has an impact of the atrp rate, this is because the ligand can change the density around copper, redox potential, Kact

What is Kact

activation rate constant, describes Pn-X→Pn*

Why is Cu (0) also usefeul in atrp

its really good at reactivating dormant chains and its also very fast. in SET-LRP

whats set lrp

A controlled radical polymerisation technique in which Cu(I) disproportionates to Cu(0) and Cu(II). Cu(0) acts as a powerful activator through single-electron transfer, generating radicals from dormant halogen-capped chains while Cu(II) provides deactivation control.

Whats the equation for set-LRP

2Cu+⇌Cu0+Cu2+

if you use ligands like Me6TREN and PMDETA, then disproportionation happens fast

why is there Cu0 and Cu 2+ in the equation

Cu0 activates and the other deactivates, BUT GENERATE THESE FIRST. then add monomer and initiator

what can SET LRP fix in normal atrp

acrylamides, bc theyre water soluble and highly polar, they cannot work for normal atrp, but set lrp converts >99 percent. dispersity values of 1.09, 1.10

whats the idea of block copolymer

AAAAAAAA-Br and before chain dies, its AAAAAAA-BBBBBBBB

Why are protic impurities problematic in living anionic polymerisation?

Protic impurities such as water and alcohols protonate the living carbanion chain end, terminating polymer growth.

Why is styrene suitable for anionic polymerisation?

The benzylic carbanion formed during propagation is resonance-stabilised by the phenyl ring.

How are functional polymers produced?

The living carbanion is reacted with an electrophile (e.g. CO₂, epoxide, alkyl halide) to introduce a desired end group before termination.

Why must anionic polymerisations be moisture free?

Water and other protic impurities protonate the living carbanion, terminating chain growth.

polystyrene radical + co makes

polystyrene radical + cyclic anhydride makes

same + epoxide

How can block copolymers be prepared?

• Sequential monomer addition – polymerise monomer A then add monomer B while chain ends remain living.

• Coupling/linking reactions – join two reactive polymer chains using a multifunctional linker.

• Macroinitiator approach – use a polymer bearing an initiating group to grow a second block.

• Transformation of active chain end – convert one living chain end into another type of initiating species before polymerising a second monomer.

how does each of copolymer block work

1) Polystyrene → add MMA → PS-b-PMMA aaaa+bbbb

2)AAAAAA-X + X-Y-X + X-BBBBBB →PS-OH + PEG-OH + diacid chloride → PS-b-PEG

3)Macroinitiator Method

AAAAAA-Br

PS-Br ATRP macroinitiator → MMA → PS-b-PMMA

4)Active Chain-End Transformation

anionic PS → convert to radical initiator → polymerise MMA → PS-b-PMMA

whats the concept of multifunctional initiators

instead of one initiator site, you have multiple

whats the concept of coupling polymerisation

Living polymer chains are reacted with a multifunctional coupling agent (e.g. dichlorodimethylsilane) to chemically join polymer blocks and form diblock or triblock copolymers such as PS-b-PB-b-PS.

why is coupling useful for ps-pb-ps

ps is hard glossy and pb is soft rubbery. together you get hard-soft-hard, this gives thermoplastic elastomer. behaves like a rubber⊕

whats the problem with anionic polymerisation with acrylates, and what can we do to get passed this. ausing side reactions and ester cleavage rather than controlled polymerisation.

anionic is ideal for styrene. acrylates create something else we dont want. to get around this we do something called GTP, group transfer polymerisation

whats GTP general idea

we use silyl ketene acetal instead of R-, its like an enolate wearing a silicone hate. here notice the end of the ketene is hte end of the propagating end, hence why polymerisation can continue. its called gtp, bc the silicon group moves everytime chains added

gtp comes under associative and dissociative pathways, what does each path entail

associative: everyones together, old bond there while new bond forms

dissociative: think sn1, si-nu breaks away, nu is usually f- catalyst

what are GTP solvent and catalyst requirements

solvent: usually polar solvents like thf, catalyst usually hard nucleophiles, F-, HF- or large gegeen ions