This document summarizes soap-free emulsion polymerization (SFEP) of styrene. SFEP avoids using surfactants by instead using oligomer chains as emulsifiers. It allows for cleaner polymer products but the mechanism is not fully understood. The document discusses the history of SFEP and proposes mechanisms involving homogeneous or micellar nucleation. It also examines how electrolytes and their properties like concentration, counter ion, and cation radius can be used to control particle size, with larger sizes resulting from higher concentrations or larger cation radii due to their impact on coagulation rates. Further study is still needed to fully elucidate the mechanism of SFEP.

1. Soap-Free Emulsion Polymerization
for Styrene
Seiji Tani , Yujing Chang, Mohammed Aljuaid

2. Outline:
 Emulsion polymerisation
 History
 Mechanism
 Particle size determination
 Conclusion
 Question
2

3. Emulsion polymerisation
 Important in industrially
 Concentration of emulsifier is above
critical micelle concentration (CMC)
 Particles are stabilized by surfactant
3

4. Polystyrene
4
SO4(M)mM• + SO4(M)nM•
SO4(M)m+n+2SO4

5. Disadvantages
 Coagulation or flocculation
 Affect the latex properties
 Hard to completely remove
5
Soap-free emulsion polymerisation

6. History
 1965, Matsumoto and Ochi:
Soap-Free emulsion polymerization
 1968-1969, Roe and Robb:
Under critical micelle concentration
 1977, Goodall et al:
Mechanism of polymerising styrene in water without surfactant
6

7. Soap-free emulsion polymerisation
 No or low concentration surfactant
 Oligomer acts as surfactant
 Clean surface products
7

8. Mechanism of soap-free
emulsion polymerization
8
PART II

9. Homogeneous nucleation:
Proposed by Fitch and co-workers
Free radical oligomer until critical length chain
The rate of coagulation is high
9

10. Micellization nucleation
Proposed by Goodall and Wilkinson
GPC data high amount of low molecular weight is constant
10
Termination of free radical oligomers!

11. Assumption:
Homogeneous + micellization nucleation
11
Coagulation rate + Oligomer chain length

12. The early stage:
12
S2O8
2- 2SO4
-•
SO4
-• + M SO4
-M•
SO4
-M• + M SO4
-MM•

13. Two possible scenarios:
First: Termination + Growth
Second : homogeneous Nucleation
13
Mechanism:

14. Embryos formation:
14
Another investigation:
Oligomers may produce:
embryos or become a
surfactant
Tetsuya Yamamoto, Yoichi Kanda, and Ko Higashitani, 2003

15. Investigation of the mechanism by
AFM:
15Tetsuya Yamamoto a , Masaki Nakayama b , Yoichi Kanda a , Ko Higashitani, 2006

16. Polymeric materials adsorbed:
16

17. Effect of electrolyte species on size of
particle through soap-free emulsion
polymerization of styrene using AIBN
and electrolyte
17
Yamamoto T and Kawaguchi K Colloid Polym Sci (2015) 293:1003–1006

18. 1. Soap-free emulsion polymerization
2. Monomer: Styrene
3. AIBN: Water-insoluble initiator
4. Electrolyte
18
Factors to consider

19. - No surfactant → Less micellar nucleation
- Less stable particles
- Submicron-sized particles in St polymerization
→ Challenge to make micron-sized particles
19
Soap-free system

20. - Low water solubility: 0.03-0.05 wt% at 20C
- Stable particles with negative charge
- pi electron density
20
Monomer (Styrene)

21. 21
Fitch-Tsai Equation
N: number of particles
Riw: initiation, Rc: capture, Rf: coagulation

22. Typical initiator for emulsion polymerization
is:
Potassium persulfate (KPS)
- Water-soluble
- Negatively charged sulfate groups
→ Less coagulation
22
Initiator

23. - Its efficiency is said to be 1/9 that of KPS
- But, works like water-soluble initiator
- forms larger particles
23
Water-insoluble initiator (AIBN)
Yamamoto, 2012
Azo initiators: Water-soluble (charged) → Water-insoluble (less charged)
AIBN

24. - Polarity of –CN group (electron attractive)
Not as strong as KPS
- Weaker repulsion (zeta potential)
than water-soluble initiator
→ Coagulation based on DLVO theory
→ Larger particles
24
Water-insoluble initiator (AIBN)

25. - Insoluble in water
- jcrit? *j=DP
- How to carry out particle formation
- Homogeneous nucleation?
- Micellar nucleation?
25
Water-insoluble initiator (AIBN)

26. :makes the particle size larger
Mechanism:
- weakens the thickness of the electrical
double layer (EDL)
- coagulation
26
Electrolyte

27. - Concentration
Higher → Larger particle
- Counter ion of the cation (pH)
- Ionic radius of cation
27
Electrolyte
0.7 mmol/L
7 mmol/L
Yamamoto, 2012

28. 28
Experimental conditions
- ca. 0.1g monomer /15g water
- ca. 3 mol initiator / 100 mol monomer
Tg of St = 100C

29. Effect of pH (Counter ion)
Low pH leads to
larger particles
29Yamamoto and Kawaguchi, 2015

30. Effect of the ionic radius of
the cation
30
Larger ionic
radius promoted
particle growth
strongly

31. Effect of the ionic radius of
the cation
31
Larger ionic radius promoted particle growth strongly
→ Low electron density
→ Weak hydration
→ Tends to retain the adsorption power of
polystyrene particle

32. Conclusion
• SFEP was successfully employed
• SFEP solves some SEP purification issues
• AFM was conducted to study mechanism, BUT,
further investigation is needed for full understanding
• Particle size can be controlled by changing pH and
species of electrolyte
32

33. References
1. Goodall, Wilkinson, Hearn (1977) J Polym Sci Pol Chem 15:2193–
218
2. T. Yamamoto et al, (2006) J Colloid and Interface Sci 297:112–121
3. Yamamoto, Kawaguchi, (2015) Colloid Polym Sci 293:1003–1006
4. Yamamoto, Kanda, Higashitani,(2004) Langmuir 20: 4400-4405
5. Chiu, Shih (1986) J of Applied Polym Sci 31:2117-2128
6. Goodwin et al, (1978) The British Polym J 10: 173-180
7. Van den Hul, Vanderhoff (1970). Polym Intern. 2(2): 121-127. 33

34. 34