PE335:

Polymerization Techniques

Techniques 2

Production Steps

Monomer

Type of polymerization

Technique/Reactor

Reaction conditions

Initiator/Catalyst

Polymer resin Compounding/Processing

End Product

Co-monomer(s)

Co-catalystsDonors etc.

Techniques 3

1. Homogeneous systems1.1. Bulk polymerization1.2. Solution polymerization

2. Heterogeneous systems2.1. Suspension polymerization2.2. Emulsion polymerization2.3. Precipitation polymerization2.4. Polymerization in solid state2.5. Polymerization in the gas phase

Polymerization Techniques

Techniques 4

Advantages and Limitations

Techniques 5

Choice of Polymerization Technique

• Kinetic / mechanistic factors related to chain length, chain composition

• Technological factors e.g. heat removal, reaction rate, viscosity of the reaction mixture, morphology of the product

• Economic factors; production costs, environmental aspects, purification steps etc.

Sometimes for one monomer several techniques of polymerizing are available. Choice of a specific technique depends on certain factors:

Techniques 6

Bulk Polymerization ● Neat monomer (and initiator)● Simplest formulation and equipment ● Most difficult in control, when polymerization is very exothermic● Common problems: (1) heat transfer (2) increase in viscosity

● If polymer is insoluble in monomer polymer precipitate (1) viscosity would remain similar (2) occlusion of radicals (within the polymer droplet) is unavoidable

● Radical occlusion autoacceleration crosslinked polymer nodules (i.e. popcorn polymerization)

● The crosslinked nodules (light weight and large volume) may cause fouling or fracture of the polymerization apparatus

Commercial uses

1. Casting formulations2. Low MW polymers for adhesives, plasticizers, tackifiers, and lubricant additives

Techniques 7

Suspension polymerization

● Disperse monomer droplets in a noncompatible liquid (e.g. H2O)● Polymerize the monomer by an initiator (soluble in the monomer) ● Stabilize the dispersion with a stabilizer (e.g. poly(vinyl alcohol) or methyl cellulose) ● Isolate granular bead products by filtration or spray drying

● Heat transfer is efficient and reaction is easily controlled● Similar to bulk polymerization in kinetics and mechanism

Commercial uses

For making granular polymers, e.g. PS, PVC, PMMA

Stabilizer

PrimaryParticles

Microdomains

MonomerDroplet

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POLYMERIZATIONREACTOR

Suspending medium(water)

Techniques 8

Solution Polymerization● Use monomer solution● Heat transfer is very efficient● MW may be severely limited by chain transfer reaction (probably caused by the solvent molecule or its impurities)

● Solvent residues difficult to remove completely● Environmental concerns organic solvent waste

Use supercritical CO2 as a polymerization solvent

nontoxic, inexpensive, easily removed and recycled

Techniques 9

Solution Polymerization

Techniques 10

Emulsification •Add emulsifying agent (e.g., soap or detergent) in an aqueous solution to form micelles• Monomers enter and swell the micellesInitiation● Radicals (redox type) are generated in the aqueous phase and diffuse into micellesPropagation● Polymerization propagated within micelles● More monomers enter micelles to support the polymerizationTermination● Termination by radical combination when a new radical enters the micelle

Results● Extremely high MW are obtainable, but often too high to be useful● Chain transfer reagents are often added to control the MW● Also suitable for tacky polymers (∵ small particles are relative stable and can resist agglomeration)

Emulsion polymerization

Techniques 11

Techniques 12

Stages of Particle Growth

Three different stages

(1)Nucleation of particles

(2)Particle growth in presence of monomer droplets

(3) Particle growth in absence of monomer droplets

(Thoenes, 1991)

Techniques 13

Emulsion Polymerization Recipe

• Water (continuous phase)

• Water-insoluble monomer

• Water-soluble initiator

• Surfactant

Techniques 14

Emulsion Polymerization Recipe

Techniques 15

Techniques 16

Techniques 17

Gas Phase Polymerization: Light olefins

Fluidized bed polymerization

Techniques 18

Hybrid Reactor for Polypropylene

3) Separation of the non-reacted monomer from the solid polymer by gasification of the (un-reacted) liquid propylene. 4) The polypropylene is washed with water vapor to eliminate any still- active catalyst, then dried with hot nitrogen. 5) PP is compounded according to the requirements of its specific application.

The process is a mass polymerization of propylene:

1) A catalytic system is prepared and made to react in a controlled manner with a small amount of liquid propylene, inside a small- capacity reactor (prepolymer)

2) The product of the pre-polymer is taken to the Loop tubular reactors (pressure of 32 bars and 70°C) for further polymerization .

Techniques 19