22
Polymer Synthesis CHEM 421 Odian Book: Chapter 4

Synthesis poly

  • View
    113

  • Download
    2

Embed Size (px)

DESCRIPTION

 

Citation preview

Page 1: Synthesis poly

Polymer SynthesisCHEM 421

Odian Book: Chapter 4

Page 2: Synthesis poly

Polymer SynthesisCHEM 421

Emulsion Polymerizations

• Economically important• Western countries 108 tons/year• 30% of all polymers made by free radical

methods–emulsion polymers accounts for 40-50% of

this

• First employed during WWII for production of synthetic rubber

• Today: MMA, VC, vinylidene chloride, styrene, fluoropolymers, vinyl acetate, EVA, SA, SBR, chloroprene, etc

Page 3: Synthesis poly

Polymer SynthesisCHEM 421

Emulsion Polymerization Recipe

• Water (continuous phase)

• Water-insoluble monomer

• Water-soluble initiator

• Surfactant (detergent)

Page 4: Synthesis poly

Polymer SynthesisCHEM 421

Surfactants

H2O

Hydrophobic /Lipophilic core

SurfactantConcentration

Unimers Micelles

Critical MicelleConcentration

(CMC)

Page 5: Synthesis poly

Polymer SynthesisCHEM 421

Surfactants

Types- Anionic

- Cationic

- Amphoterics

- Non-ionics

Page 6: Synthesis poly

Polymer SynthesisCHEM 421

Emulsion Polymerization Recipe

Page 7: Synthesis poly

Polymer SynthesisCHEM 421

Emulsion Polymerizations

Polym’zRate

Surfactant Concentration

Critical Micelle Concentration

Page 8: Synthesis poly

Polymer SynthesisCHEM 421

Kinetics of Emulsion Polymerization

PercentConversion

Time

I

II

III

Page 9: Synthesis poly

Polymer SynthesisCHEM 421

Kinetics of Emulsion Polymerization

Rate

% Conversion

I II III

Page 10: Synthesis poly

Polymer SynthesisCHEM 421

Before Initiation

II

I

II

I

I I

I

M

M

MM

MM

M

MM M

MM

M

M

M

M

M

M

M

Monomer Dropletca. 1 micron diameter

conc = 1011/mLstabilized by soap

Micelle Containing Monomer

ca. 75 Å diameterconc = 1018/mL

Relative surface area1 : 560

Initiation of micelles statistically favored

Page 11: Synthesis poly

Polymer SynthesisCHEM 421

Interval One: 0 – 15 % Conversion

I •I

I

II

I

I • I

I

M

M

MM

MM M

M

M

M

MM

M

PP••

PP••

M M

MicellesContaining Monomer

Activelatex particle

MicellesContaining Monomer

MicellesContaining Monomer

Activelatex particles

Inactivelatex particles

Inactivelatex particles

Page 12: Synthesis poly

Polymer SynthesisCHEM 421

Qualitative Details

Conversion Micelles Monomer

Droplets

Particle

Number

Particle

Size

Comments

I0 – 15% present present increases increases

Nucleation period,

Increasing Rp

II

III

Page 13: Synthesis poly

Polymer SynthesisCHEM 421

Interval Two: 15 – 80% Conversion

I

II

I

I • I

I

M

M

MM

M

M

MM

M

PP••

PP•• I •I

M

M

PP••

Inactivelatex particles

Inactivelatex particles

Inactivelatex particles

Activelatex particles

Activelatex particles

I •I

M

PP••Active

latex particles

No micelles

Number of particles constant, therefore

Rp = constant

Page 14: Synthesis poly

Polymer SynthesisCHEM 421

Kinetics of Emulsion Polymerization

Number ofMicelles

Time

I II III

Number ofPolymerParticles

1018

0

1015

0

Page 15: Synthesis poly

Polymer SynthesisCHEM 421

Qualitative Details

Conversion Micelles Monomer

Droplets

Particle

Number

Particle

Size

Comments

I0 – 15% present present increases increases

Nucleation period,

Increasing Rp

II15 – 80% absent present constant increases

Constant # of particles,

Cp = constant

III

Page 16: Synthesis poly

Polymer SynthesisCHEM 421

Interval Three: 80 – 100% Conversion

I

II

I

I • I

M

M

MM

M

M

M

PP••

PP••I

M

M

PP••

I •M

PP••M

PP••

M

PP••

I •

No monomer droplets

No micelles

Page 17: Synthesis poly

Polymer SynthesisCHEM 421

Qualitative Details

Conversion Micelles Monomer

Droplets

Particle

Number

Particle

Size

Comments

I0 – 15% present present increases increases

Nucleation period,

Increasing Rp

II15 – 80% absent present constant increases

Constant # of particles,

Cp = constant

III80 – 100% absent absent constant roughly

constant

Constant # of particles,

Cp = decreasing

Page 18: Synthesis poly

Polymer SynthesisCHEM 421

Emulsion Polymerization Kinetics

• Once inside a particle, radical propagates as rp = kp[M]

• Overall rate: Rp = kp[M][P.]

• [P.] = N’ñ (where N’ = the sum of micelle and particle concentrations and ñ = average # of radicals per particle)

• Therefore,

–Increase N’ to increase rate!

][' MknNR pp

Page 19: Synthesis poly

Polymer SynthesisCHEM 421

Emulsion Kinetics, cont.

• Smith-Ewart Kinetics:

–Case 2: ñ = 0.5 (MOST CASES!)

» 1 radical per particle

» Half of the particles active, half not active

–Case 1: ñ<0.5

» Radical can diffuse out of the particle

» Monomer with higher water solubility

–Case 3: ñ>0.5

» Termination constant is low

» High viscosity, initiator; large particles

Page 20: Synthesis poly

Polymer SynthesisCHEM 421

Emulsion Polymerization Kinetics

• How to increase Rp?

–Increase N’ to increase rate

»Increase surfactant concentration to increase N’

][' MknNR pp

Page 21: Synthesis poly

Polymer SynthesisCHEM 421

Molecular Weight in Emulsion Polymerizations

• Molecular weight determined by rate of growth of a chain divided by rate of radical entry (ri)

–How to increase molecular weight?

DPrp = ——ri

Ri = ——N

ri = kp[M]rp

N kp [M]

Ri

= ———DP

Page 22: Synthesis poly

Polymer SynthesisCHEM 421

Free Radical Solution Polymerizations

• Recall

– To increase molecular weight…

» Increase monomer concentration

» Decrease initiator concentration

– To increase Rate of Polymerization

» Increase monomer concentration

» Increase initiator concentration

٧ =kp [M]

2 (kt kd f [I])1/2 = —————

Can’t doboth!

Rp = kp [M] (kd f [I] / kt)1/2