Advanced Polymer Synthesis

Tutorial on Macromolecular Engineering

Axel MllerMakromolekulare Chemie II

www.MCII.de

ENB Elite Study Program Macromolecular Science Lecture on August 28, 2007

Tutorial on Macromolecular Engineering

A. Mechanisms of Living Polymerization

B. Synthesis and Properties of Block Copolymers

LiteratureMechanisms:G. Odian: "Principles of Polymerization", 4th Ed., Wiley, New York 2004Mark-Bikales-Overberger-Menges, Eds.: "Encyclopedia of Polymer Science and Engineering", 2nd Ed., Vol 1-

17+ Suppl. , Wiley, New York, 1985-89. Contains numerous review articles from "Anionic Polymerization" (Vol. 2, p. 1) via "Living Polymer Systems" (Suppl. Vol., p. 380) to "Zwitterionic Polymerization" (Vol. 17, p. 1028).

G. Allen, J.C. Bevington, Eds.: "Comprehensive Polymer Science", Vol. 3+4: Chain Polymerization, Pergamon Press, Oxford 1989 (very detailed review articles on mechanisms and properties)

Macromolecular Engineering in general:G. Allen, J.C. Bevington, Eds.: "Comprehensive Polymer Science", Pergamon Press, Oxford 1989; Vol. 6,

chapters 8-13 (p. 227-436), Vol. 7, chapter 1, Suppl. Vol. 1 (1992); p. 83-106H.L. Hsieh, R.P. Quirk: "Anionic Polymerization: Principles and Practical Applications",

Marcel Dekker, New York 1996Y. Gnanou: "Design and Synthesis of New Model Polymers", J. Macromol. Sci.-Rev. Macromol. Chem. Phys.,

C36, 77 (1996)J. C. Salamone (Ed.): Polymeric Materials Encyclopedia, CRC Press, Boca Raton (1996) K. Hatada, T. Kitayama, Eds.: "Macromolecular Design of Polymeric Materials", M. Dekker, New. York, 1997K. M. Stridsberg, M. Ryner, A.C. Albertsson: Controlled Ring-Opening Polymerization: Polymers with

Designed Macromolecular Architecture Adv. Polym. Sci. 157, 42 (2002)

Block copolymers:I.W. Hamley, The Physics of Block Copolymers, Oxford University Press 1998M. Pitsikalis, S. Pispas, J.W. Mays, N. Hadjichristidis, "Nonlinear Block Copolymer Architectures, Adv. Polym.

Sci. 134, 1 (1998)N. Hadjichristidis, S. Pispas, G. A. Floudas, Block Copolymers: Synthetic Strategies, Physical Properties,

and Applications; Wiley-Interscience, 2003

Polymer Architecture

Topology Composition Molecular weightdistribution

Functionality

Microstructure

R R R R R R R R R

R

R

R

R

R

R

R

R

R

X

XX

X XX X

XX

X

XX

XXX

Polymer Properties

X X X X X X X X X

X

Part A:

Mechanisms of Living Polymerization

Anionic Polymerization

Cationic Polymerization

Ring-Opening Polymerization (anionic, cationic)

Living/Controlled Radical Polymerization

Basic Principles of Living Polymerization

When termination and transfer are absent

(Rt, Rtr

Conditions for a Living Polymerization (1)1. No Termination: kt = 0The number of active chain-ends [P*] is constant:Evidence:First-order kinetics with respect to monomer concentration:

[ ]

renders nIntegratio

bygivenistionpolymeriza ofrateThe

*]P][M[M pp kdtdR ==

[ ][ ] tktk appp == *]P[MM

ln 0

Conditions for a Living Polymerization (2)

Pn

[ ][ ]

[ ][ ]0

00

IM

PM

chainspolymer ofnumber monomers dpolymerize ofnumber

pp

n

xx

P

==

=

2. No Transfer: ktr = 0

There are no new chains formed,

the total number of polymer chains, [P], (including the terminated ones!)

is constant: [P] = [P*] + [Pdead] = [I]0Evidence:the number-average degree of polymerization,

,is a linear function of monomer conversion, xp:

Molecular Weight Distribution (MWD)Ideally, a very narrow MWD is expected, the Poisson distribution(Flory, 1940).The polydispersity index is given by

MM

PP P

w

n

n

n n

= +

+ 11

11

12

Factors leading to broader MWD'sNon-living Processes: termination Mw/Mn 2 (important for anionic polymerization of (meth)acrylates) transfer Mw/Mn 2 (important in cationic polymerization of isobutylene)

Living Processes: inadequate mixing:

tmix > t1/2 Mw/Mn can be very high slow initiation:

ki < kp Mw/Mn 1.33 reversible polymerization ("scrambling"):

Mw/Mn 2 slow equilibria between species of different activity:

Rex < Rp Mw/Mn can be very high (important for many "new" living/controlled processes)

Controlled Polymerization

[ ][ ]

[ ][ ]00

0

IM

IM

== pnx

P

nw MM /

is a synthetic method to obtain polymers where: the number-average degree of polymerization is given by ratio of monomer over initiator:

MWD is narrow:

all chains can be functionalized: Pi* + X Pi-X

< 1.1 or 1.2

This is obtained if: the rate of initiation and rate of exchange reactions between various active species

are fast compared to propagation (Rex, Ri > Rp).

chain-breaking reactions (termination or transfer) are not too strong (Rt, Rtr

Anionic Polymerization

~~~~~C + C=C ~~~~~C-C-C

R R R R

M. Szwarc, 1956:Living Polymers

Nature 178, 1168 (1956)

Important Monomers1. Non-polar vinyl compounds (with strong delocalization): styrene, -methyl styrene o-, m-,p-alkyl styrenes vinyl naphthalene dienes (butadiene, isoprene, )

2. Polar electrophilic vinyl compounds (with electron attracting substiuents): vinyl pyridine (meth)acrylates N,N-dialkyl acrylamides (meth)acrylonitrile

3. Cyclic Ethers, Esters, Siloxanes, ...:Ring-Opening Polymerization

Protected MonomersMonomers with acidic hydrogens need to be protected:

2-hydroxyethyl methacrylate (HEMA)

solketal methacrylate

methacrylic acidAS tert-BUTYL ESTER:

Initiators1. Organometallic bases (monofunctional):

- organolithium: n-BuLi, s-BuLi, t-BuLi - alcoholates (t-BuO-Li, t-BuO-K, ...)- alkali salts of aromatic hydrocarbons: benzyl-Na, cumyl-K, ...

2. Electron transfer agents (bifunctional):- alkali metals (heterogeneous):

- radical anions: naphthalene sodium (homogeneous):

Special Considerations for Experimental WorkDue to the high nucleophilicity of the initiators (and propagating chain ends) it is absolutely necessary to avoid oxygen, water and protic impurities:This implies

- aprotic solvents:polar: THF, ...non-polar: toluene, cyclohexane, hexane, ...

- rigorous purification of reagents- handling of reagents in vacuum or under inert gas.

Due to the absence of termination, the concentration of active species can be much higher than in radical polymerization. Thus, the rates sometimes can be very high(e.g., t1/2 < 1 s for MMA in THF at room temperature).

In order to control the polymerization it may be necessary to - use specially designed reactors (fast mixing: flow tube)- add monomer slowly (vapour phase)- work at low temperatures (-78 C)

First-Order Plot of Kinetics kapp = kp[P*]is the slope of the first-order plot

Linear plot (constant slope)[P*] = const. no terminationfast initiation

Polymerization of styrene with Na+ counterion in THF

Anionic Polymerizaton of Non-Polar Monomers

G.V. Schulz et al., Makromol. Chem. 71, 198 (1964)

(+) T = 24 C(o) T = -28 C

Molecular Weight vs. Conversion

Linear plot (constant slope)the number of all chains, [P], is constant

no transferfast initiation

Mw/Mn < 1.02

Cationic Polymerization

~~~~~C + C=C ~~~~~C-C-C

R R R R

M. Sawamoto, T. Higashimura, 1979

Monomers

: isobutylene ( low Tg rubber, low permeability)

: PS-b-PIB-b-PS: excellent thermoplastic elastomer

: poly(methyl vinyl ether) is water-soluble

Initiators

Protic Acids: HClO4, CF3SO3H, ...

Stable cations

Photoinitiatorsh

Lewis Acids: AlCl3, BF3, : H2O + BF3 H+(OH)BF3-

Living Polymerization Initiators

2,4,4-Trimethylpentyl-2-chloride(TMP-Cl)

monofunctional

1,3-Di(2-chloro-2-propyl)-5-tert.-butylbenzene (tBu-DiCum-Cl)

bifunctional

In situ generation of halides from HI and vinyl ethers:

Catalyst necessary to generate cations!

Living Polymerization of Isobutylene

Termination by Protons:

K

Conclusions: Cationic Polymerization

Living cationic polymerization depends on a catalyzeddynamic equilibrium between dormant (inactive, covalent) and active species (ion pairs, free cations)

The rate of polymerization is determined by the position of the dissociation and aggregation equilibria.

Transfer" (spontaneous and to monomer) is the main sidereaction; it can be minimized by using larger counterions

and highly polar solvents.

Ring-Opening Polymerization (ROP)

X-Y~~~~~~X-Y~~~~~~

R or R

Anionic ROP (AROP)

Cationic ROP (CROP)

Ring-Opening Metathesis Polymerization (ROMP)

Anionic Ring-Opening Polymerization (AROP)Monomers (1):

Nucleophilic Substitution linear anionic chain end

Ethylene Oxide, Propylene Oxide

Propylene Sulfide

O

Monomers (2)

lactide -caprolactam N-carboxyanhydrides

polypeptides

small cycles alkyl split

larger cycles acyl split

(initiation with RLi, ROLi)

Nylon 6

silicones

Cationic Ring-Opening Polymerization (CROP)Some monomers

THF

azridines oxazolines

1,3-dioxolane + trioxane POM

phosphazenes

Mechanism of Living CROP of THF

Equilibrium polymerization!

Living CROP of Oxazolines

Methyl oxazoline (MeOX)

Hor

OH

Linear poly(ethylene imine)

polyMeOX: water-soluble

polyBuOX: hydrophobic

Controlled/Living Radical Polymerization

Nitroxide-Mediated Polymerization (NMP)E. Rizzardo, M. Georges 1992

Atom Transfer Radical Polymerization (ATRP)K. Matyjaszewski, M. Sawamoto 1994

Reversible Addition-Fragmentation Chain Transfer (RAFT)E. Rizzardo, G. Moad, S. Thang 1996

~~~~~C + C=C ~~~~~C-C-C

R R R R

Controlled/Living Radical Polymerization

>5,000 papers on CRP(>3,000 ATRP since 95)

>600 patents on CRP(>400 ATRP since 95)

Anticipated market:>20$billion/yearBob Matheson (DuPont)

Applications:coatings, adhesives,surfactants, dispersants,lubricants, gels, additives,thermoplastic elastomers,electronics, biomaterials, Specialties

SciFinder Scholar: September 14, 2005

0

1 0 0

2 0 0

3 0 0

4 0 0

5 0 0

6 0 0

7 0 0

8 0 0

2005

2004

2003

2002

2001

2000

1999

1998

1997

1996

1995

1994

C R P & L R P

A T R P o n ly

S F R P & N M P

R A F T & D T & C C T

Y e a r

Num

ber o

f Pub

licat

ions

/Yea

r

Polymerizability of Monomers

Radical Polymerization works for the largest number of monomers!

Very many monomer pairs can be copolymerized

Undemanding reaction conditions (just remove oxygen)

Problems of Conventional Radical Polymerization1. Termination via fast bimolecular radical-radical reactions:- Recombination: ~~~Pn + Pm~~~ ~~~Pn+m~~~- Disproportionation:

~~~CH2-CH + CH-CH2~~~ ~~~CH=CH + CH2-CH2~~~X X X X

Radical lifetime is in the range of milliseconds!

2. Transfer to monomer, polymer, solvent, :- Generates new chains: ~~~CH2-CH + Y ~~~CH=CH + H-Y

X X

Decreasing Termination by Dilution of Chain Ends:

1. Reversible Deactivation of Chain Ends

Dynamic equilibrium between active and dormant species

propag-ation

Solution:reversible

deactivation(endcapping)

Bob Gilbert

+ R

+ M

+X

+ MX = persistent radical:

X = nitroxide, e.g., TEMPO NMP, SFRP

X = transition metal halide, e.g. CuBr2 ATRP

Problem:Termination by

Recombination or Disproportionation

Nitroxide-Mediated Polymerization (NMP)

alkoxyamine radical persistent radical

Advantages: Simple, many (functional) nitroxides available Radicals can be formed by classical initiators or from alkoxyamines works well in emulsion and miniemulsion Mw/Mn < 1.2 possible

Disadvantages: slow, high temperatures needed (> 100 C) works for few monomers only (styrene, acrylates)

M. Georges, 1994

Partial library of alkoxyamine structures evaluated as initiators for the living radical polymerization of styrene and n-butyl acrylate.

Braslau, Hawker

SG1(diethylphosphonate)

Tordo, Gnanou

Atom Transfer Radical Polymerization (ATRP)(Transition Metal Mediated Polymerization)

K. Matyjaszewski, M. Sawamoto, 1995

Advantages: Simple; many metal ions (Fe, Ni, ) and ligands available works for most monomers (not acrylic acid, ) No conventional initiator needed Mw/Mn < 1.2 possibleDisadvantages: removal of catalyst on large scale difficult does not work for monomers that complex the Mt ion (acrylic acid, )

NNCuN N

Br CuN

NPn Br

NNPn+ +

ka ~ 1 M-1.s-1

kd ~ 107 M-1.s-1

+ M

3 1 1

Chemistry

Note: Values (M-1s-1) are measured with EtBriB/Cu(I)Br in AN at 35 C. N2: red, N3: green, N4: blue; Amine/imine: solid, Pyridine: open, Mixed: left-half solid; Linear: , Branched: , Cyclic: .

Some Ligands

-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3

log(ka)Extrapolated Values

N N

NN

N[2,3,2] (1.2 10-3)

N N

N[3,2,3] (5 10-3)

N N

N N

N

N[2,2,3] (0.23)

NN N

NN

N[2,2,2] (HMTETA) (0.14)

N

N N

N[2,3] (9.2 10-3)

N

NR

NPPMI: R=C3H7 NOPMI: R=C8H17(2.4 10-3)

N

NN

PMDETA (N[2,2]) (2.7)N

N

N

N

TPMA (62.4)

N N

N N

Cyclam (Nick) (708.7)

N

N

N

N

Me4Cyclam (0.67)N

N N

N

PyNMeNMePy (4.5)

N Nbpy (0.092)

N N

dNbpy (0.6)

NNN

N

O

nBu

O

O

BunO

OBun

OnBu

OnBu

O

nBu

O

O

O

O

BA6TREN (4.09)

NNN

N

O

O

OO

OO

O

O

O

O

O

O

MA6TREN (1.23)

NNN

N

Me6TREN (455.6)

NNN

N

Et6TREN (0.044)

NNN

N

CN

NC

NC CN

CN

CN

AN6TREN (0.012)

N N

TMEDA (0.042)

Active

Some Initiators

S

CH3O

ClO

O

Bulk ATRP of Styrene

2. Reversible TransferDegenerative Transfer between active and dormant chains:

~~~Pm-I + Pn~~~ ~~~Pm + I-Pn~~~ where [P-I] >> [P ]

Reversible Addition-Fragmentation Chain Transfer (RAFT) Polymerization

Rizzardo, Moad 1998

Addition / fragmentation:

Equilibration:

Propagation:

dormant dormantdormant activeactive

Initiation: initiator + monomer Pm

PnMonomer

Rki

Re-inintiation: Pn+1Monomer

Pnkp

Z

S S PnPm

Z

SS Pn+

Pm S S

Z

+PmPn

M M(2)

k

k

k-

k-

chain transfer agent

dormantdormant

Z

SS R+

Z

S S RPmPm

Pm S S

ZR+

k-,1k,1

k,1k-,1

are thiocarbonylthio compounds:

Z CS

SR Z = alkyl, aryl, N ...

R = alkyl, aryl

R' CS

SR R'S CS

SR

R' O CS

SR SRR'R''N CS

dithioester trithiocarbonate

xanthateMADIX

(Rhodia 1999)

dithiocarbamate

Chain Transfer Agents (CTAs)

, RO-, RS- (stabilizes radical)

(leaving group): reinitiates polymerization,can carry functional groups

RAFT of N-isopropylacrylamide (NIPAAm)Synthesis of polyNIPAAm via RAFT with

dithiocarbamates as chain transfer agents

benzyl 1-pyrrolecarbodithioate cumyl 1-pyrrolecarbodithioate

Chain transfer agents used:

CH2 CH

NHiPrO

CH2 CH

NHiPrO

R SS

Zn

CTA, AIBN

60 C, dioxane

N

SS CH2Ph

N

SS CCH3

CH3Ph

Conclusions: Controlled Radical Polymerization

Controlled Radical Polymerization proceeds either by

Reversible Deactivation (NMR, ATRP) or by

Reversible Transfer (Degenrative Transfer, RAFT).

The rate of polymerization depends on the position of the

activation equilibrium.

The MWD depends on the dynamics of the activation

equilibrium.

Termination cannot be completely avoided.

Transfer is not affected by CRP.

Comparison of Living Mechanisms

Pro ConRadical Low purity requirements (cheap)

Convenient temperatures (cheap)Large variety of monomersBlock copolymersRandom copolymersGradient copolymers

Expensive nitroxides, CTAsRemoval of metals difficultVery few cyclic monomers for ROPSome terminationNo control of transfer low MWLittle control of microstructure

Ionic No (little) termination or transfer Block copolymersHigh MWROP possibleSome control of microstructure

Termination or transfer (some cases)High purity, low T (expensive)Choice of monomers restrictedRandom copolymers difficult

Part B

Synthesis and Properties of Block Copolymers

Synthesis of linear block copolymers

Sequential monomer addition

Polymer-polymer coupling

AB

ABC

2 x AB

ABA

ABA

Problem: low coupling efficiencies

+

Sequential monomer addition

I- I~~~~MA-MB

Good blocking efficiency when the reactivityof the first block is higher or comparable tothat of the second block.

MAI~~~~~~~~~MB-

Attenuation of the reactivity of the first blockmay be necessary in order to avoid sidereactions in the cross-over step.

PS- + DPE PS-DPE-

MMA

PS-PMMA

MCI~~~~~~~~~~~~~~MC-

macroinitiator

Special Case: RAFT

R CH2 CH CH2

OHO

CH

NHiPrO

SS

Zm n

CH2 CH

OHO

SSNC

NO

m

NIPAAm, AIBN

MeOH, 60 C

Macro-chain transfer agent

Bifunctional initiation

-I-I- + MB -MB~~~~~~I-I~~~~~~MB-

MA

~~~~~~~~~~~~~~~~~~~~~I-I~~~~~~~~~~~~~~~~~~~~~

Problem:

Most important properties:

Most important applications:

Bifunctional initiators are not well soluble in hydrocarbon solvents (due to aggregation)

Microphase separation in bulkMicelle formation in solution

SBS, thermoplastic elastomers (Kraton)PPO-PEO-PPO, amphiphilic copolymers (Pluronics)

Anionic bifunctional initiators for non-polar solvents

Phase diagram and topology of diblock copolymers in bulk

Hexagonal cylinders(H)

BCC spheres(QIm3m)

_

Gyroid(QIa3d)

_

PS-PB-PS cubic (spherical) morphologyPS-b-PI lamellar morphology

TEM

OsO4

SAXS

Morphologies of triblock terpolymers(found with S-B-M)

knitting pattern

R. Stadler et al.

S-EP-M

hard (high Tg)

PS, PMMA

hard

Thermoplastic elastomers based on ABA bock copolymers

PB, PIB, PnBA

soft (low Tg) microphase

separation

physical cross-linking

reversible!

Superstructures of Amphiphilic Diblock Copolymers

star micelle

Crew-cut micelle vesicle

incorporation of OmpF

cylinder vesicle(nanotube)

Cryo-TEM of micelles at high pH

100 nm

Collapsed core surrounded by an extended corona

Rcore ~ 5 nmRmicelle ~ 30 - 50 nm (?)Rh ~ 50 nm (DLS)Lcontour (PAA) = 75 nm

PnBA90-b-PAA300

Advanced Polymer Synthesis Tutorial on Macromolecular EngineeringLiteraturePolymer ArchitectureFoliennummer 5Basic Principles of Living PolymerizationConditions for a Living Polymerization (1)Conditions for a Living Polymerization (2)Molecular Weight Distribution (MWD)Controlled PolymerizationAnionic PolymerizationImportant MonomersProtected MonomersInitiatorsSpecial Considerations for Experimental WorkFirst-Order Plot of KineticsMolecular Weight vs. ConversionCationic PolymerizationMonomersInitiatorsLiving Polymerization InitiatorsLiving Polymerization of IsobutyleneConclusions: Cationic PolymerizationFoliennummer 24Anionic Ring-Opening Polymerization (AROP)Monomers (2)Foliennummer 27Mechanism of Living CROP of THFLiving CROP of OxazolinesControlled/Living Radical PolymerizationControlled/Living Radical PolymerizationPolymerizability of MonomersProblems of Conventional Radical Polymerization1. Reversible Deactivation of Chain EndsNitroxide-Mediated Polymerization (NMP)Foliennummer 36Atom Transfer Radical Polymerization (ATRP)(Transition Metal Mediated Polymerization)Some LigandsFoliennummer 39Bulk ATRP of Styrene2. Reversible TransferFoliennummer 42Foliennummer 43Foliennummer 44Conclusions: Controlled Radical PolymerizationComparison of Living MechanismsFoliennummer 47Foliennummer 48Foliennummer 49Foliennummer 50Foliennummer 51Foliennummer 52Phase diagram and topology of diblock copolymers in bulkFoliennummer 54Morphologies of triblock terpolymers(found with S-B-M)Foliennummer 56Foliennummer 57Foliennummer 58