Synthesis of Controlled Polymer Nanospheres by a ... · PDF fileFragmentation Chain Transfer (RAFT) Miniemulsion Polymerization ... Reversible Addition-Fragmentation Chain Transfer

Synthesis of Controlled Polymer Nanospheres by a Reversible Addition-Fragmentation Chain Transfer (RAFT)

Miniemulsion Polymerization

Huije Lee, Sang Eun Shim, Byung H. Lee, Soonja Choe*

Department of Chemical Engineering, Inha University,

253 Yonghyundong, Namgu, Incheon

402-751, S. Korea

Polymer Materials Lab. Inha University


ObjectivesTo apply a RAFT agent bearing carboxyl acid group tominiemulsion polymerizationTo obtain stability-enhanced functionalized polymernanospheres with narrow PDI via RAFT method

Introduction

Copolymerization with ionicmonomersPolymerization with charge endowing surfactants or initiatorsMulti-step process in which functional groups are introduced after the colloid synthesis

◈ Synthetic methods of functionalized particles

Colloidal drug carrier,detoxification Solid-phase supports inbiomedical and biochemical fieldsInformation technologyMaterials for humidity sensors ….

◈ Applications


Living Free-Radical Polymerizations

◈ Characteristics of LRPPrecise control of Mn & PDIPrecise control of stereostructureSynthesis of highly functional block copolymersTailor-made polymer products Advanced materials applicable to IT, BT, and NT

◈ LRP MethodsReversible Addition-Fragmentation Chain Transfer Polymerization(RAFT)Nitroxide-Mediated Polymerization (NMP)Atom-Transfer Radical Polymerization (ATRP)


Trend in LRPs

Stable Radicals: Stable Radicals: GombergGomberg

1900 1900 …… 1980 1980 8282 8686 1990 1990 95 95 9898 2000 2000

Timeline of LRP

Living Radical Polymerization (Living Radical Polymerization (IniferterIniferter): ): OtsuOtsuNMP: Solomon & NMP: Solomon & RizzardoRizzardo

ATRP: ATRP: MatyjaszewskiMatyjaszewski

RAFT: RAFT: RizzardoRizzardo

Heterogeneous:Miniemulsion

Heterogeneous:Emulsion

Homogeneous:Bulk / Solution

Research Interest in LRPs

Molecular Design in Homogeneous Polymerization

1.

2.


RAFT Polymerization

X

Z

RX

Weak single bond R is free radical leaving group (R· must also be able to reinitiate polymerization)

Reactive double bond

Z modifies addition and fragmentation rates

◈ Generic RAFT Agent Structure

CSS CH2 COOH

(4-Toluic acid) dithiobenzoate, TADB

CSS CH2

Benzyl dithiobenzoate, BDB


Mechanism of RAFT PolymerizationInitiation

Chain transfer

Reinitiation

Chain equilibration

Termination

InitiatorM

PnI

Pn

M Ph

S S R+

Kadd

K-add

SPn

Ph

S R K β

K -β

SPn

Ph

S + R

RMki

R MMkp

Pm

Pn

M Ph

S S Pn+ SPm

Ph

S Pn SPm

Ph

S + Pn

M

Pn + Pmkt dead polymer


RAFT Polymerization

◈ Problems in conventional emulsion polymerizationLack of colloidal stabilityRetardation of polymerization rateFormation of a conspicuous red layer at the beginning of polymerizationBroad molecular weight distribution (higher than 1.5)

◈ Techniques utilized to overcome the problemsSemi-batch processSeeded emulsion polymerizationMiniemulsion polymerization


Experimental

Recipe- Reaction medium : double distilled de-ionized (DDI) water- Monomer : Methyl methacrylate, Styrene- Surfactant : Sodium dodecyl sulfate (SDS)- Cosurfactant : Hexadecane- Initiator : 2,2’ – Azobis(isobutyronitrile) (AIBN)- RAFT agent : (4-Toluic acid) dithiobenzoate, Benzyl dithiobenzoateConditions- 60 – 80OC, 220 rpm- [RAFT]/[AIBN] = 0, 1, 2, 5Characterizations- Molecular weight measurement : GPC

HPLC pump (WATERS 510), Viscometer (Viscotex)- Particle size and Zeta potential : Zetasizer (Malvern, Zetasizer 4000)- Conductivity measurement : Conductivity meter (KEM, GM - 115)- Analysis of particle size & morphology : SEM (Hitachi, S - 4300)


Experimental Results

◈ Polymerization Kinetics : Effect of Reaction Temperature([TADB]/[AIBN]=1), PMMA

Polymerization Time (min)0 20 40 60 80 100 120 140 160 180

Frac

tiona

l Con

vers

ion

0.0

0.2

0.4

0.6

0.8

1.060oC70oC80oC

Polymerization Time (min)0 20 40 60 80 100 120 140 160 180

Ln{[

M] 0

/[M]}

0.0

0.5

1.0

1.5

2.0

2.5

3.060oC70oC80oC



◈ Molecular Weight Evolution : Effect of Reaction Temperature([TADB]/[AIBN]=1), PMMA

Fractional Conversion 0.0 0.2 0.4 0.6 0.8 1.0

Num

ber-

aver

age

Mol

ecul

ar W

eigh

t

20000

30000

40000

50000

60000

70000

80000

90000

100000 60oC 70oC 80oC

Fractional Conversion0.0 0.2 0.4 0.6 0.8 1.0

PDI

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.860oC70oC80oC



◈ Polymerization Kinetics : Effect of [TADB]/[AIBN], 80oC PMMA

Polymerizaion Time (min)

0 20 40 60 80 100 120

Frac

tiona

l Con

vers

ion

0.0

0.2

0.4

0.6

0.8

1.0

0125

Polymerization Time (min)0 20 40 60 80 100 120

Ln{[

M] 0

/[M]}

0.0

0.5

1.0

1.5

2.0

2.5

3.00125



◈ Molecular Weight Evolution : Effect of [TADB]/[AIBN], 80oC PMMA


PDI

1.01.21.41.61.82.0

4.0

5.0

0125


Num

ber A

vera

ge M

olec

ular

Wei

ght

0

10000

20000

30000

40000

50000

60000

70000

80000

90000

100000

0125



◈ GPC Traces & SEM Photograph of PMMA : 2hr, 80oC

Retention Time (min)5 10 15 20 25

0 1 2 5

[TADB]/[AIBN]

[TADB]/[AIBN]=1, 90nm


MI

MonomerInitiator COOH RAFT agent (TADB)

Surfactant

a

COO

H H2O

H2O

H2O

M

MM

M

M

MI

I

II

I

I II

H2OCOO-

COOHCOO-

COO-COOH

M

M M

MI

I

I

I I

COOH

COO- COO-M

MI

I

I

COOH

COO-

d c

b

COO

-

COO-

COOH

COOH

COO-

COO-

COO

-

COO

H

COO

-

COO-

COOH

COOH

COO-

COO-

COO

-

MM

M

III

Stirring

More

Heating

Synthetic Mechanism


◈ Particle Size Distribution of PMMA Latex : 2hr, 80oC

Size (nm)0 100 200 300 400 500 600

Inte

nsity

[TADB] / [AIBN] = 0[TADB] / [AIBN] = 1[TADB] / [AIBN] = 2[TADB] / [AIBN] = 5

0125

[TADB] / [AIBN]0 1 2 3 4 5

Size

(nm

)

40

50

60

70

80

90

100

110

120



◈ Zeta Potential & Conductivity of PMMA Latex : 2hr, 80oC

Zeta potential (mV)-70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50

Inte

nsity

[TADB] / [AIBN] = 0[TADB] / [AIBN] = 1[TADB] / [AIBN] = 2[TADB] / [AIBN] = 5

0125

[TADB] / [AIBN] 0 1 2 3 4 5 6

Zeta

pot

entia

l (m

V)

-50

-45

-40

-35

-30

-25

-20

Con

duct

ivity

(mS/

cm)

2.02.12.22.32.42.52.62.72.82.93.0




◈ Polymerization Characteristics : Effect of carboxyl acid [RAFT]/[AIBN] = 1.3, 80℃, PS

Reaction Time (hr)0 1 2 3 4 5 6 7 8

Ln{[

M] 0

/[M]}

0.00.20.40.60.81.01.21.41.61.82.0

TADBBDB

Fractional Conversion0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

Mn

0

10000

20000

30000

40000

50000

60000

70000

80000

90000TADBBDB


PDI

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6TADBBDB

CSS CH2 COOHTADB : C

SS CH2BDB :


Experimental Results◈ Influence of RAFT agents : Particle size, Zeta potential,

and Conductivity (8hr), PS

Particle Size (nm)Particle Size (nm)

Conductivity (Conductivity (mSmS/cm)/cm)

Zeta potential (mV)Zeta potential (mV)

TABD BDB[RAFT]/[Initiator] = 1.3

125.1 135.7

-48.2 -44.5

2.60 2.48

SEM imagesSEM images



◈ Polymerization Characteristics : Effect of [TADB]/[AIBN],80℃, PS

Reaction Time (hr)0 1 2 3 4 5 6 7 8

Ln{[

M] o

/[M]}

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0123


Num

ber A

vera

ge M

olec

ular

Wei

ght

0

5000

10000

15000

20000

80000

100000

1200000123


PDI

1.01.21.41.61.82.02.22.43.0

3.5 0123


Experimental Results◈ Average Particle Size & SEM Photographs of PS : 8hr, 80oC



[TADB]/[AIBN]0 1 2 3 4

Ave

rage

Par

ticle

Siz

e (n

m)

90

100

110

120

130



◈ Zeta Potential & Conductivity of PS Latex : 8hr, 80oC

[TADB]/[AIBN]0 1 2 3

Zeta

Pot

entia

l (m

V)

-55

-54

-53

-52

-51

-50

-49

-48

[TADB]/[AIBN]0 1 2 3

Con

duct

ivity

(mS/

cm)

3.4

3.5

3.6

3.7

3.8

3.9

4.0

4.1

4.2

4.3


A linear increase in Mn with respect to the conversion is observed, indicating the nature of living (controlled) radical polymerization.

The PMMA-system

- The higher the temperature, the faster conversion, the lower Mnand PDI are obtained.

- As the ratio of [TABD]/[AIBN] increases, the conversion, molecular weight, molecular weight distribution, and particle size decrease.

- With the ratio of [TABD]/[AIBN], the zeta potential & conductivity increase, i.e. the stability of the PMMA latex is enhanced.

Conclusions


The PS-system

- A BDB (w/o carboxyl acid functionalized)-added system leads to slower conversion, similar Mn and PDI, and larger particle size, however, decreases the zeta potential and conductivity.

- As the ratio of [TABD]/[AIBN] increases, the conversion, molecular weight, and molecular weight distribution decrease, however, particle size increases.

- With the ratio of [TABD]/[AIBN], the zeta potential & conductivity increase, i.e. the stability of the PS latex is enhanced.

The polymer nanospheres functionalized with carboxylic acid group can be prepared by a novel mechanism.

Conclusions

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Synthesis of Controlled Polymer Nanospheres by a ... · PDF fileFragmentation Chain Transfer (RAFT) Miniemulsion Polymerization ... Reversible Addition-Fragmentation Chain Transfer