Synthesis of Controlled Polymer
Nanospheres by a Reversible AdditionFragmentation 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
Objectives
To apply a RAFT agent bearing carboxyl acid group to
miniemulsion polymerization
To obtain stability-enhanced functionalized polymer
nanospheres with narrow PDI via RAFT method
Introduction
◈ Synthetic methods
of functionalized particles
Copolymerization with ionic
monomers
Polymerization with charge
endowing surfactants or initiators
Multi-step process in which
functional groups are introduced
after the colloid synthesis
◈ Applications
Colloidal drug carrier,
detoxification
Solid-phase supports in
biomedical and biochemical fields
Information technology
Materials for humidity sensors ….
Polymer Materials Lab. Inha University
Living Free-Radical Polymerizations
◈ LRP Methods
Reversible Addition-Fragmentation Chain Transfer Polymerization
(RAFT)
Nitroxide-Mediated Polymerization (NMP)
Atom-Transfer Radical Polymerization (ATRP)
◈ Characteristics of LRP
Precise control of Mn & PDI
Precise control of stereostructure
Synthesis of highly functional block copolymers
Tailor-made polymer products
Advanced materials applicable to IT, BT, and NT
Polymer Materials Lab. Inha University
Trend in LRPs
Timeline of LRP
1900
…
1980
82
86
1990
95
98
2000
Stable Radicals: Gomberg
Living Radical Polymerization (Iniferter): Otsu
NMP: Solomon & Rizzardo
ATRP: Matyjaszewski
RAFT: Rizzardo
Research Interest in LRPs
1.
2.
Homogeneous:
Bulk / Solution
Heterogeneous:
Miniemulsion
Heterogeneous:
Emulsion
Molecular Design in
Homogeneous Polymerization
Polymer Materials Lab. Inha University
RAFT Polymerization
◈
Generic RAFT Agent Structure
Weak single bond
Reactive
double bond
R
X
X
Z
S
C S CH2
R is free radical leaving
group (R· must also be
able to reinitiate
polymerization)
Z modifies addition
and fragmentation
rates
COOH
(4-Toluic acid)
dithiobenzoate, TADB
S
C S CH2
Benzyl
dithiobenzoate, BDB
Polymer Materials Lab. Inha University
Mechanism of RAFT Polymerization
Initiation
M
Initiator
I
Pn
Chain transfer
Pn
+
M
S
S R
Kadd
Pn S
K-add
Ph
S R
Kβ
K -β
Ph
Pn S
S
+
R
Ph
Reinitiation
M
ki
R
R M
M
kp
Pm
Chain equilibration
Pn
+
S
M
S Pn
Pm S
Ph
S Pn
Ph
Pm S
S +
Ph
Pn
M
Termination
Pn
+
Pm
kt
dead polymer
Polymer Materials Lab. Inha University
RAFT Polymerization
◈ Problems in conventional emulsion polymerization
Lack of colloidal stability
Retardation of polymerization rate
Formation of a conspicuous red layer at the beginning of polymerization
Broad molecular weight distribution (higher than 1.5)
◈ Techniques utilized to overcome the problems
Semi-batch process
Seeded emulsion polymerization
Miniemulsion polymerization
Polymer Materials Lab. Inha University
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 dithiobenzoate
Conditions
- 60 – 80OC, 220 rpm
- [RAFT]/[AIBN] = 0, 1, 2, 5
Characterizations
- 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)
Polymer Materials Lab. Inha University
Experimental Results
◈ Polymerization Kinetics : Effect of Reaction Temperature
([TADB]/[AIBN]=1), PMMA
3.0
0.8
0.6
0.4
0.2
0.0
o
60oC
70oC
80oC
60 C
70oC
80oC
2.5
Ln{[M]0/[M]}
Fractional Conversion
1.0
2.0
1.5
1.0
0.5
0
20 40 60 80 100 120 140 160 180
Polymerization Time (min)
0.0
0
20 40 60 80 100 120 140 160 180
Polymerization Time (min)
Polymer Materials Lab. Inha University
Experimental Results
2.8
100000
60oC
70oC
80oC
90000
80000
2.4
70000
2.2
60000
2.0
50000
1.8
1.6
40000
1.4
30000
1.2
20000
0.0
60oC
70oC
80oC
2.6
PDI
Number-average Molecular Weight
◈ Molecular Weight Evolution : Effect of Reaction Temperature
([TADB]/[AIBN]=1), PMMA
0.2
0.4
0.6
Fractional Conversion
0.8
1.0
1.0
0.0
0.2
0.4
0.6
0.8
1.0
Fractional Conversion
Polymer Materials Lab. Inha University
Experimental Results
◈ Polymerization Kinetics : Effect of [TADB]/[AIBN], 80oC
PMMA
3.0
0.6
0
1
2
5
0.4
0.2
0.0
0
1
2
5
2.5
0.8
Ln{[M]0/[M]}
Fractional Conversion
1.0
2.0
1.5
1.0
0.5
0
20
40
60
80
100
Polymerizaion Time (min)
120
0.0
0
20
40
60
80
100
120
Polymerization Time (min)
Polymer Materials Lab. Inha University
Experimental Results
100000
5.0
90000
80000
4.0
70000
60000
PDI
Number Average Molecular Weight
◈ Molecular Weight Evolution : Effect of [TADB]/[AIBN], 80oC
PMMA
50000
40000
1.8
0
1
2
5
30000
20000
10000
1.6
1.4
1.2
0
0.0
2.0
0.2
0.4
0.6
Fractional Conversion
0.8
0
1
2
5
1.0
1.0
0.0
0.2
0.4
0.6
0.8
1.0
Fractional Conversion
Polymer Materials Lab. Inha University
Experimental Results
◈ GPC Traces & SEM Photograph of PMMA : 2hr, 80oC
[TADB]/[AIBN]
0
5
12 5
10
15
20
Retention Time (min)
25
[TADB]/[AIBN]=1, 90nm
Polymer Materials Lab. Inha University
Synthetic Mechanism
CO
O
H
COO
Heating
H
COO
COO -
I
COO-
H
COO
COO -
H
COO
H2O
H2O
Surfactant
Monomer
Initiator
I M I
M I
M
COO -
I
H
COO
COO -
M
M
I
COOH
M
COO -
-
c
-
COOH
O
CO
M
COO -
I
M
COO-
H2O
More
d
I
I
COO
M
I
Stirring
I
-
M
M I
I
COOM
M
I
O
CO
I
I
M
I
H
COO-
I
b
CO
O
I
H2O
COOH
M
COOM
I
COOH
COO-
a
COOH
RAFT agent (TADB)
Polymer Materials Lab. Inha University
-
Experimental Results
◈ Particle Size Distribution of PMMA Latex : 2hr, 80oC
52 1 0
120
[TADB] / [AIBN] = 0
[TADB] / [AIBN] = 1
[TADB] / [AIBN] = 2
[TADB] / [AIBN] = 5
110
Intensity
Size (nm)
100
90
80
70
60
50
0
100
200
300
Size (nm)
400
500
600
40
0
1
2
3
[TADB] / [AIBN]
4
5
Polymer Materials Lab. Inha University
Experimental Results
◈ Zeta Potential & Conductivity of PMMA Latex : 2hr, 80oC
3.0
-20
2.8
2.7
-30
2.6
2.5
-35
2.4
-40
2.3
2.2
-45
-70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50
Zeta potential (mV)
-50
Conductivity (mS/cm)
2.9
-25
Zeta potential (mV)
[TADB] / [AIBN] = 0
[TADB] / [AIBN] = 1
[TADB] / [AIBN] = 2
[TADB] / [AIBN] = 5
Intensity
5 2
1 0
2.1
0
1
2
3
4
[TADB] / [AIBN]
5
6
2.0
Polymer Materials Lab. Inha University
Experimental Results
◈ Polymerization Characteristics : Effect of carboxyl acid
[RAFT]/[AIBN] = 1.3, 80℃, PS
2.0
90000
1.6
70000
1.4
1.2
Mn
Ln{[M]0/[M]}
80000
TADB
BDB
1.0
0.8
60000
2.2
50000
2.0
40000
0.4
20000
0.2
10000
0
1
2
3
4
5
6
7
8
TADB :
1.4
Fractional Conversion
S
C S CH 2
COOH
1.8
1.6
0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Reaction Time (hr)
TADB
BDB
2.4
30000
0.6
0.0
2.6
TADB
BDB
PDI
1.8
BDB :
1.2
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Fractional Conversion
S
C S CH2
Polymer Materials Lab. Inha University
Experimental Results
◈ Influence of RAFT agents : Particle size, Zeta potential,
and Conductivity (8hr), PS
[RAFT]/[Initiator] = 1.3
TABD
BDB
Particle Size (nm)
125.1
135.7
Zeta potential (mV)
-48.2
-44.5
Conductivity (mS/cm)
2.60
2.48
SEM images
Polymer Materials Lab. Inha University
Experimental Results
◈ Polymerization Characteristics : Effect of [TADB]/[AIBN],
80℃, PS
1.4
0
1
2
3
Ln{[M]o/[M]}
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
1
2
3
4
5
6
Reaction Time (hr)
7
8
120000
100000
3.5
0
1
2
3
80000
20000
PDI
Number Average Molecular Weight
1.6
15000
10000
5000
0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Fractional Conversion
0
1
2
3
3.0
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Fractional Conversion
Polymer Materials Lab. Inha University
Experimental Results
◈ Average Particle Size & SEM Photographs of PS : 8hr, 80oC
Average Particle Size (nm)
130
120
110
[TADB]/[AIBN]=0, 90nm
100
90
0
1
2
3
4
[TADB]/[AIBN]
[TADB]/[AIBN]=3, 125nm
Polymer Materials Lab. Inha University
Experimental Results
◈ Zeta Potential & Conductivity of PS Latex : 8hr, 80oC
4.3
-48
4.2
Conductivity (mS/cm)
Zeta Potential (mV)
-49
-50
-51
-52
-53
-54
-55
4.1
4.0
3.9
3.8
3.7
3.6
3.5
0
1
2
[TADB]/[AIBN]
3
3.4
0
1
2
3
[TADB]/[AIBN]
Polymer Materials Lab. Inha University
Conclusions
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 Mn
and 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.
Polymer Materials Lab. Inha University
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.
Polymer Materials Lab. Inha University