Virginia Tech: Polymer Materials and Interfaces LaboratoryVirginia Tech: Polymer Materials and Interfaces Laboratory

Emulsion Polymerization of StyreneEmulsion Polymerization of Styrene

General Kinetic Features and Particle Size Ranges of Heterogeneous (Particle

Forming) Polymerization Processes

0.01 0.1 1.0 10 100 1000 Particle Size Range (m)

Emulsion Polymer

Emulsifier Free Emulsion Polymer

Dispersion Polymerization

Precipitation PolymerizationDirect Conversion of Monomer Droplets

Suspension Polymerization

PolymerParticles

Nucleation

and G

rowth

Mechanisms of Emulsion PolymerizationInitially 3 Components:1. Colloidally dispersed soap micelles

swollen with monomer, diameter ~50Å (50 to 100 soap molecules per micelle)

2. Macrodroplets of Monomer stabilized by soap, diameter ~15,000Å

3. Aqueous PhaseA. InitiatorB. Electrolyte to stabilize latexC. Possibly a Buffer

Soap Concentration

Rat

e of

Pol

ymer

izat

ion

Soap Concentration

Rat

e of

Pol

ymer

izat

ion Critical Micelle

Concentration

Emulsion Polymerization Scheme

MonomerDroplet

PolymerMonomer

Monomer Micelle

Continuous Phase:

WaterI R.

soap

Polymerization Process

• Set up reactor apparatus and set oil bath to 75ºC• Disperse 0.5 g sodium lauryl sulfate (surfactant)

in 55 mL oxygen-free H2O for 5 minutes in the reactor (CMC is met)

• Add 22 mL styrene (monomer), wait 3-5 minutes (diffusion into micelles) and add 0.05 g potassium persulfate dissolved in 5 mL H2O (initiate particle formation)

• After polymerization, coagulate polymer in concentrated alum solution, wash with methanol, filter by suction and dry in a vacuum oven overnight.

Number of Polymer Particles

N = k (Ri/ )2/ 5(asS)3/ 5

N = Number of ParticlesS = Surfactant Concentrationas = Interfacial Surface areaRi = Rate of Initiation = Rate of Increase of Volume

High particle numbers associated with small particle size

Time (hrs)

Con

vers

ion (%

)20

40

60

80

100

Time (hrs)

Con

vers

ion (%

)20

40

60

80

100

Emulsion Polymerization Kinetic Stages

INTERVAL IMonomer in micelles (dia ~50 Å)Monomer in droplets (dia ~ 106Å)Monomer in polymer particlesGrowing number of particles

INTERVAL IINo Micellar SoapMonomer in DropletsMonomer in Polymer ParticlesConstant Number of Particles

INTERVAL IIINo DropletsMonomer in Polymer ParticlesConstant Number of Particles

III

III

EmulsionPolymerization

•ADVANTAGES- Faster Rates- Higher Molecular Weights- Good Heat Transfer- May be directly usable (Latex)- 500-5000Å

• DISADVANTAGES-Recovery of solid polymer more difficult-Removal of emulsifier difficult

C a t e g o r i e s o f S u r f a c t a n t s• A n i o n i c

– C a r b o x y l a t e s ( s o a p s )

– A l k y l b e n z e n e s u l f o n a t e s

• N o n i o n i c– A l k y l p h e n o l e t h o x y l a t e s

– E t h y l e n e o x i d e / P r o p y l e n e o x i d e c o p o l y m e r s

• C a t i o n i c– B e n z y l t r i m e t h y l a m m o n i u m b r o m i d e

R

O

O N a

R S O 3 N a

R O

OH

n

O

O

C H 3

O H

Hn m

N +

H 3 CC H 3

C H 3

B r -

Rate of Emulsion Polymerization

Rp= kp [M]N/2N A

Rp = Rate of Emulsion PznKp = Rate Constant[M]= Monomer ConcentrationN= Number of Particles= Avogadro’ Number

Emulsion Polymerization

Emulsion Polymerization Scheme