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Athina Flashcards

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1
Q

Charachteristics of Step Growth polymerization

A
  • No initiation step
  • MW grows at 90% conversion
  • Only polym. where monomers ≠ RU
  • Growth doesn’t stop once monomer consumed
  • Chains could recombine
  • Polym. stops at high MW because chains cannot propagate easily
  • No initiation step, dispersity high, high livingness
    –> example PET
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2
Q

Charachetristics of “Living” Chain Growth polymerization

A
  • MW grows linearly (MW predictable)
  • Anionic: Fast and parallel initiation
  • No/little termination
  • Lowest dispersity among other techniques
  • No. final chains = No. initiators
  • Initiaton only at the beginning
  • Polym. stops when monomer is consumed
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3
Q

Charachetristics of Conventional Chain Growth polymerization

A
  • Immediately formation of high MW chain
  • FRP: slow and Continuous initiation
  • Chain die through growth -> new initiator starts
  • Dispersity is high
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4
Q

Peculiarities of FRP

A
  • Only 50% of initiator contribution
  • More radicals -> shorter chains
  • Recombination visible by GPC, disproportionation no
  • Blockcopolymer cannot be made by FRP
  • Polymer grow because we push radicals conc. to low levels -> meets a monomer instead of another radical
  • High dispersity >1.5
  • Difference with living -> no reactive chain ends
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5
Q

Advantages of FRP

A
  • Very simple system (consists of 2 or 3 components only)
  • Easy to perform (you simply mix everything together)
  • It works for any monomer that has a double bond
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6
Q

Disadvantages of FRP

A
  • Cannot make block copolymers
  • Cannot control molecular weight and dispersity
  • Difficult to control branching and architectures
  • No functional end-group for further reactions (e.g. click chemistry with biomolecules)
  • Does not work for monomers without double bond
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7
Q

Acid triggered FRP

A

The lower the pH, the faster the polymerization but without increasing the # of free radicals –> termination rate do not increase
- Acid forms radicals
- Acid lowers the free energy barrier of initiation and propagation
–> lower dispersity and higher Mn respect to conventional FRP

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8
Q

Peculiarities of ATRP

A
  • Radical lives for very short time.
  • Wants to react back with Br.
  • Only few monomer per step.
  • Prop slower than act/decat, but faster than termination.
  • Ligand makes CuBr soluble and stable.
  • If monomer has acid -> ligand could be protonated.
  • Mw limited to <100.kDa
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9
Q

Advantages of ATRP

A
  • Extremely adaptable
  • Simple, relatively inexpensive reagents & conditions
  • Overall broad monomer scope
  • Typically narrowest MWDs of all CRP techniques
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10
Q

Disadvantages of ATRP

A
  • Requires many components
  • Picking the “correct” variety of ATRP is not always easy
  • Struggles with some monomer types
  • Not very industrialized yet
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11
Q

Advantages of RAFT

A
  • Widest monomer scope of any CRP technique
  • Can, pretty uniquely, control the polymerization of low-reactivity monomers
  • Operationally very simple (FRP + 1 reagent)
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12
Q

Peculiarities of RAFT

A
  • Thiols can act as reversible CT agent -> can control MW
  • Different from NMP and ATRP -> free radical initiator in RAFT do not contain deactivator
  • We want pre-equilibrium to be fast
  • CTA consumed immediately
  • Degenerate -> start with radical and CTA, ends with radical and CTA
  • CTA caps chain but uncaps another that can propagate
  • 2 chains grow in parallel
  • Pn = [M]0/[CTA]
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13
Q

Definition of “Living” Polymerization

A

Chain growth process in which termination and CT reactions are absent or strongly suppressed.

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14
Q

Benefits of starting with CuBr2

A
  • CuBr2 more stable than CuBr -> storage easier
  • You have less termination
  • Higher MW and better blockcopol
  • No need of lot of catalyst
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15
Q

Disadvantages of RAFT

A
  • RAFT CTAs are often expensive and sometimes not very stable
  • No truly “universal” CTAs
  • Slightly broader MWDs than e.g. ATRP, particularly for block copolymers
  • CTAs sensitive to strong nucleophiles
  • Not very industrialized yet
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16
Q

SARA-ATRP

A

Supplementary Activation and Reducing Agent - ATRP

CuBr (Cu(I)) is the main activator (wins over Cu(0) because is very stable.
Cu(0) and Cu(II) comproportionate (react with each other) to give CuBr

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17
Q

Photo-ATRP

A

UV light helps reducing Cu(II) –> Cu(I)

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18
Q

ICAR-ATRP

A

Initiators for Continuous Activator Regeneration
Thermal radiation helps reducing Cu(II) –> Cu(I)

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19
Q

SET-ATRP

A

Single Electron Transfer-ATRP

Cu(0) is the main activator because more stable than CuBr (Cu(I))
CuBr disproportionates to produce Cu(0) and Cu(II)
Disproportionation of Cu(I) wins over the activation of Cu(I).

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20
Q

Advantages of Cu(0) ATRP

A
  • It uses significantly lower amounts of copper catalyst. (remaining Cu(0) catalyst is not soluble and can
    be removed from the polymerization by lifting the wire out)
  • It works at room temperature
    (conventional ATRP needs high temperatures)
  • Goes to higher conversions than conventional ATRP and has higher end-group fidelity
    (small amounts of copper cause less termination)
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21
Q

Disadvantages of Cu(0) ATRP

A
  • Cannot reach as high molecular weights as conventional ATRP (because it is at room temperature)
  • Does not work well with some monomers (like styrene)
  • Exact amount of catalyst is hard to calculate (causing reproducibility issues)
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22
Q

Oxygen-Tolerant polymerization

A

The components can consume oxygen and then the polymerization can start.
The catalyst is formed under ambient atmosphere the polymerization is much faster than under inert condition.

–> very high end group fidelity polymers

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23
Q

Oxygen-Tolerant ATRP

A
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24
Q

Why oxygen-tolerance has such effect on polymerization?

A

The reason behind this acceleration is thought to be the formation of a superoxido.
–> efficient Synthesis of One-Pot Multiblock Copolymers, Synthesis of High Molecular Weight Polymers, Various Monomers and No Need to Purify CuBr for this Synthesis

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25
Q

Metal-free ATRP

A

We avoid a lot of side reactions, e.g. the coordination of Cu with something else.
Problem: metal free is a new method and gives high dispersity and just work with styrene and methacrylate

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26
Q

PET-RAFT

A

Photoinduced Electron Transfer RAFT

  • No need to add radical initiator (it operates at low T so it can polymerize more monomers with fewer side reactions) –> less termination and amount of Ir (photoredox catalyst) compared to the radical initiator amount is less.
  • Wide range of monomers and solvents
  • Temporal controlled polymerization
  • Different choice of catalyst
  • Ultrahigh MW achieved
  • Oxygen tolerant
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27
Q

SONO-RAFT

A

No AIBN needed, initiation by hydroxy radicals (splitting of water by ultrasound)

Advantages:
- No need to add radical initiator
- Temporally controlled polymerization is the biggest advantage

Problems:
1. we add radicals so termination is equal to conventional RAFT
2. No control over the # of radicals
3. Limited achievable MW due to ultrasound can cut long polymer chains to short.

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28
Q

Solid Phase Peptide Synthesis pros (+) and cons (-)

A

+ Perfect sequence control (monodispersed materials)
- Time consuming
- Expensive
- Limited to low molecular weights
- Difficult to scale up (mg scale)

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29
Q

Photoiniferter RAFT polymerization

A

photo-initiator, transfer-agent and termination agent.

Molecule that could act as initiator, transfer agent and termination agent

  • No exogenous initiator is required
  • Can reach high MW with low dispersity
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30
Q

Coupling existing polymers (Building Blocks) pros and cons

A

+ High DP and molecular weight achieved.
+ Compatible with various synthetic methods and many types of
monomers.
+ Degradable polymers via selecting linkers.
- Limited number of blocks.
- High contamination unless purification (fractionation to remove cycles).
- No “true” sequence control

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31
Q

Criteria for Successful Synthesis of Sequence-Controlled
Multiblock Copolymers

A
  • Narrow Molecular Weight Distributions for Each Block (Ð < 1.5)
  • High End-Group Fidelity (indirectly shown by several blocks > 5)
  • Quantitative or Near-Quantitative Conversions for Each Block (> 95%) otherwise we have contamination i.e. not pure materials!
  • No purification steps involved between each monomer addition
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32
Q

Anionic polymerization for sequence controlled multiblock copolymers pros and cons

A

+ High molecular weight (~200 kg mol-1) and very low dispersity (<1.1) achieved
+ High purity of blocks formed (little tailing in SEC traces)
- Limited monomer choice (issue of Living Anionic Polymerization)
- Limited number of blocks (issue of addition monomers without contamination)
- Tedious and time-consuming procedure (difficult for non-experts)

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33
Q

Sequence-Controlled Multiblock Copolymers: Overall Strategy for Radical Polymerizations

A

Optimised conditions needed to achieve:
* very fast polymerization
* minimized termination and side reactions even at very high conversion

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34
Q

Sequence-Controlled Multiblock Copolymers: Difficulties with
ATRP

A

Termination can still happen at any “radical stage” and even more at high conversion when the monomer concentration is low (when monomer content is low, radicals can meet each other)

35
Q

Sequence-Controlled Multiblock Copolymers: Difficulties with
RAFT

A

Although the RAFT agent ensures that the radicals spend most of their time in the dormant state, termination is dictated by the initial amount of free radical initiator. Termination will also more likely happen at high conversion when the monomer concentration is low.

36
Q

Why is termination higher for star polymers?

A

More bromines attached = higher chance of termination (more Br = more radical site can initiate coupling)

37
Q

Self Assembly in Solution for Amphiphilic Copolymers

A
  1. Dissolve PS-PEG in organic solvent where both block are soluble
  2. Slowly add water to organic solution via a syringe pump
  3. Micelles as end product
38
Q

Why do we get different shapes in the amphiphilic copolymers synthesis?

A

Due to the different nature of the various solvents and due to the Critical Packing Parameter p=v/a*l where v is the hydrophobic chain volume, l is the length of hydrophobic chain and a is the effective interfacial area

39
Q

Which factors affect the morphology of traditional self assembly of amphiphilic copolymers?

A
  • Copolymer concenetration
  • Water content
  • Molecular weight
40
Q

Advantages of Traditional Self-Assembly in Solution

A

+ Simple procedure
+ Suitable for a variety of monomers

41
Q

Disadvantages of Traditional Self-Assembly in Solution

A
  • Multiple parameters affect the morphology (e.g., solvent, water addition rate, polymer concentration, salt concentration, etc.)
  • Each block copolymer requires different optimised parameter (good news – one paper can be published for every new diblock you use to see different shapes)
  • Small scale (mg) and diluted (typically below 10 mg per 1 mL)
  • Make block polymer and assembly in 2 steps (synthesis + self assembly)
42
Q

Polymerization Induced Self-Assembly (PISA)

A
  1. Water soluble Macro CTA fully dissolved (Block 1)
  2. Add second water soluble monomer (Block 2)
  3. Diblock copolymer is formed
  4. Second block becomes big and becomes hydrophobic
  5. Block 1 (hydrophilic) outside forming the corona and Block 2 inside, hidden in the core of the spherical particle.

When the polymerization starts, also the self assembly does.

43
Q

Why with PISA no vesicles nor worms are formed?

A

Because the initial spherical shape is trapped due to high Tg of PS which makes the structure rigid;
PHMPA has on the other hand a low Tg hence more flexible and the morphology is no trapped –> can form worms, vesicles, lamellae, jellyfish, …

44
Q

Why is Photo-PISA used?

A

To access different morphologies

45
Q

What is Oxygen-Tolerant PISA useful for?

A

Easier synthesis at very low volumes, so without wasting materials (monomer, solvents, etc.)

46
Q

Advantages of PISA

A

+ One step making nanoparticles with different shapes
+ Scalable and concentrated (up to 50% weight) –> higher chance to be commercialised

47
Q

Disadvanatges of PISA

A
  • Shape is affected by DP (batch to batch difference)
  • Limited polymer choice (not all polymers can form worms and vesicles)
  • Requiring high temperature (issue for some applications)
  • Need expertise in RAFT polymerization
  • Need to do in a chemistry lab (degas, oil bath, stirring, etc.)
  • Cannot control the length of worms
  • Different shapes have molecular weight
48
Q

Temperature Induced Morphological Transformation (TIMT)

A

Goal: Make a diblock: one hydrophilic and one thermoresponsive (soluble at RT but insoluble in water at higher T).
1. Put Block 1 at water @ high T and so you form hydrophobic particles (stabilised by surfactants)
2. Add in a second hydrophobic monomer which will slowly enter the particles to polymerize yielding a double hydrophobic diblock copolymer.
3. Upon cooling @ RT the thermoresponsive block becomes hydrophilic yielding an amphiphilic diblock copolymer that can rearrange to form different morphologies

49
Q

What is the plasticiser in TIMT?

A

If PS is the 2nd block, then the plasticiser will be something with similar solubility to PS, e.g. Toulene, which can enter the core and allow for flexibility.

50
Q

Which effect has the amount of plasticiser on TIMT?

A

We obtain different shapes, since PS is rigid and is in the core, a temperature change is not sufficient to trigger a change in shape –> plasticiser gives mobility

51
Q

Advantages of TIMT

A

+ One diblock copolymer results in different shapes
+ Scalable and concentrated (similar to PISA)
+ No need for self-assembly step (but requires transformation step)

52
Q

Disadvantages of TIMT

A
  • Limited to thermoresponsive polymers
  • Requiring high temperature (issue for some applications)
  • Need expertise in RAFT emulsion polymerization
  • Need to do in a chemistry lab (degas, oil bath, stirring, etc.)
  • Cannot control the length of worms
53
Q

Transformer Induced Metamorphosis (TIM) of polymeric nanoparicle’s shape at RT

A

Technique that involves the addition of a transformer to change the shape of polymeric nanoparticles. Examples: toluene or styrene

54
Q

What is the role of the transformer in TIM?

A

It swells the core of the nanoparticle and increase the critical packing parameter p=v/a*l

55
Q

What’s the key advantage of TIM?

A

The chemical structure and MW of block copolymers remain intact (NMR show similar chemical structure and SEC traces show identical MW distribution)

56
Q

Crystallization-Driven Self-Assembly (CDSA)

A
  1. Diblock copolymer (universe = monomers) put in a solvent in which can crystallise
  2. One block crystallizes, the other not, so we obtain a polydisperse not uniform fibers.

Then you can whether:
a. Self seeding: gentle sonication to make short fibers and then apply heat to detach some of the unimers and finally cool down to recrystallise to form monodisperse fibers.
b. Seeded growth: vigorous sonication to break into very short fibers and add more unimers to continue the crystallisation to finally grow monodisperse fibers.

57
Q

Applications of TIM

A
  1. In traditional self assembly –> adding toluene to go from worms to vesicles
  2. In organic PISA –> increasing the amount of transformer yields vesicles starting with worms, crossing the two phases sphere with arms and jellyfish
  3. In aqueous PISA –> increasing the amount of transformer we got from spheres to worms, to vesicles. Also the properties of the solutions change drastically (sphere –> liquid, worms –> gel, vesicles –> cloudy suspension)
58
Q

Key point of Self-Seeding method in CDSA

A

+ Very simple to do
- Cannot control the length very well as there are limited unimers that can be detached
- Cannot have different unimer added

59
Q

Key point of Seeded-Growth method in CDSA

A

+ Can add unimers continuously and the fibers will keep growing
+ Can add different unimers (different block copolymers) allowing to make diblock fibers
- More time consuming

60
Q

Advantages of CDSA

A

+ Best technique to control the length of worms
+ Mixture of different block copolymers (tuneable surface property)
+ Growing in 2D and superstructure

61
Q

Disadvantages of CDSA

A
  • Limited to semi-crystalline polymers in the core
  • Time consuming (take weeks for growing)
  • Cannot encapsulate cargos (affect the crystallite polymers in the core)
  • You cannot make different morphologies like vesicles
  • Cannot make a soft material –> it crystallizes in the core!
62
Q

Why we cannot in Self assembly or in PISA control the length of the worms?

A

In Pisa we can only change the length of the hydrophobic but by doing that you may change the morphology (kinetically controlled)

In CDSA is more thermodynamically controlled system, so it assumes stable worms.

63
Q

Applications of polymeric nanoparticles made from block copolymers

A
  1. Drug delivery: encapsule hydrophobic drugs in the hydrophobic core of particles to protect, increase solubility and increase circulation of the drugs. PROBLEM: to make miscelles release drugs you need one block (hydrophobic) to be pH responsive –> deprotonation and drug release
  2. Ultra pH sensitive nano probe: to detect something, e.g. tumor. When the polymers are not assembled then those two are far away and
    you can see colour
  3. To enhance MRI contrast agents: encapsulate MRI contrast agent in the core of polymeric np to give better signal.
  4. As nanoreactors: to protect catalyst from degradation in solvents, increase catalysts solubility and increase local concentration of catalyst at reaction site
64
Q

Applications of nanoworms

A
  1. Catalysis: as nano reactor to encapsulate silver nanoparticles containing e.g. methylene blue, to be disposable
  2. As gels for storage application: network of worms at high T and as you cool down you arm spheres, e.g. to preserve red blood cells at RT
  3. Immunotherapy: nanoworms binds to T-cell and trigger immune repsonse because of large surface area of nanoworms increase the chance that one antibodies bind to T-cell which can then activate
  4. Drug delivery: nanoworms have longer circulation and deeper penetration in tumours than spheres
65
Q

Why chemical recycling materials are relevant?

A
  1. Reduce plastics entering landfill sites
  2. Plastic waste would become a valuable resource to produce new materials for polymer’s industry
66
Q

Why is easier to depolymerise RAFT/ATRP?

A

Because of carbon-raft agent and carbon-sulfide bond is easier than breaking a C-C bond or a C-H bond of FRP.

67
Q

Mechanical recycling main problem

A

Melt an re-process the polymer but the properties cannot survives such high temperatures –> downcycling

68
Q

Pyrolisis to chemical recycling polymers made by FRP

A

PMA heated up and in a big polymer chain, carbon-carbon bonds are broken and form a lot of radicals anywhere in the backbone and eventually the radicals go back to the monomer.

69
Q

Disadvantages of pyrolisis to chemical recycling polymers made by FRP

A
  • Extremely High Temperatures are Required
  • A lot of Energy is Being Consumed
  • Side Reactions Occur which Contaminate the Monomer Regeneration with Side Products (Impure mixtures are retrieved, money spent to separate them)
  • Dead Polymer Chains/No Active Chain-end

How to solve them?
One idea to alleviate these issues is to pre-install end-groups much easier to cleave (e.g. more labile) and this can happen via ATRP and RAFT polymerization.

70
Q

What is the K_poly?

A

Is the rate constant which describe the equilibrium between polymerization and depolymerization.

A polymerization will occur until a certain monomer concentration is reached at which the rate of propagation and the propagation become equal: k_poly = k_depo/k_poly which means that high monomer concentration = low depolymerization.

High [Monomer] =.low k_poly = low depolymerization

71
Q

How to trigger a depolymerization?

A
  1. Chain end activation is important to produce active species
  2. High T helps
  3. High dilution helps
  4. Removing the monomer helps
72
Q

When a monomer becomes a polymer the change in entropy ∆S is … and the change in enthalpy ∆H is …

A

∆S < 0 because the freedom of the system is decreased and ∆H < 0 because a double bond becomes sigma bond so the system gains energy.

The polymer state then has a non favourable entropy because less freedom, so what we gain in term of enthalpy H must compensate the loss of freedom of a monomer –> that is why polymers can form!

73
Q

What is the Ceiling Temperature?

A

T above which, in a given chain polymerization, polymer of high molar mass is not formed, or better the T at which the rate of polymerization and depolymerization are equal.

Above T_ceil depolymerization wins, and the opposite.

If an active species was put into solution at a given temperature, depolymerization would proceed until the MEC is reached for this temperature. The addition of monomer to a solution of propagating species at a given temperature, would result in overall polymerization until enough monomer is consumed to reach the MEC for this temperature

74
Q

Why polymers made by FRP depolymerise at 400 degree and the one made by RAFT at 70?

A

FRP polymers are kinetically trapped, they don’t have weak chain-end that can be easily cleaved to produce a radical. Even thermodynamics say yes, kinetics says a strong NO to depolymerization.

75
Q

Importance of reverse controlled radical polymerization

A
  1. Sustainability
  2. Industrial commercialisation: reduce costs
  3. Reveal new mechanisms to polymer chemistry
76
Q

Depolymerization of RAFT synthesised polymers

A

GPC traces show an uncontrolled depolymerization, i.e. when a radical is formed at the end of the chain, in a second a monomer is formed. MW remains roughly the same.

It works with every type of monomers, disregarding the nature (hydrophobic, aromatic, pH responsive, semifluorinated, etc.)

The more diluted, the more depolymerise well for a fixed T.

For a fixed concentration, the higher T the better the depolymerization

77
Q

Opportunities through depolymerization of RAFT polymers?

A
  1. Retrieve starting materials and can re-polymerize
  2. Retrieve starting materials can form entirely new materials
  3. Regeneration of heat sensitive monomers without side reactions
78
Q

Thermal ATRP Depolymerization key points

A
  • Lower conversion achieved than RAFT, max 71%.
  • Required T = 170 degree
  • @ 120 degree we get 46% of monomer regeneration vs. RAFT @ 120 degree reaches 92%
79
Q

Why depolymerization of ATRP polymers stops?

A
  • Side reaction kills the end-group and we no longer have active chain-ends
  • Initial polymer was not of 100% end-group fidelity so if the initial end-group fidelity
    was 80% then the max depo conversion would also be 80%
  • We have reached the thermodynamic limits; equilibrium monomer concentration
  • We introduced oxygen and we have killed the depropagating radicals
  • Not sufficient end-group activation is available
80
Q

Advantages of photocatalitic depolymeriozation of ATRP polymers

A

+ efficient initiation
+ lower T
+ Fast radical formation. = fast rate
+ Spatio-temporal control
+ Higher yield

81
Q

How to avoid side reactions during depo of ATRP polymers?

A

Use Cl instead of Br: C-Cl is a more table bond, so we can protect the chain end

82
Q

Controlled Depolymerization

A

Idea is to simultaneously cut off the end groups and interrupt the depol. whenever we want. To do that, deactivation must be faster than propagation.

How?
1. use low concentration of chains (5mM) and add RAFT agent
2. Use a high concentration of initial polymer (120mM)

We can discover what we had in block copolymer or in random copolymers.

83
Q

Trick to suppress thermal initiation to have temporal control and a higher conversion at lower T?

A
  1. Combine light with heat: lower the T of depo and still achieve high conversion BUT no temporal control because:
    - high amount of activator
    - thermal part is never zero
  2. Low catalyst loading: the participation of thermal depolymerization is minimal like 5% and the photo thermal is 85%. Temporal control is improved but not perfect
  3. Replacing the activator FeCl2 with a deactivator FeCl3: we create fewer radicals that are immediately consumed when the light is off and the depol. does not continue. –> temporal control near as perfect!

Chemistry of Soft Materials (5 decks)

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