PE335: Polymerization Techniques

Production Steps End Product Monomer Co-monomer(s) Type of polymerization Co-catalysts Donors etc. Initiator/Catalyst Technique/Reactor Reaction conditions Polymer resin Compounding/Processing Techniques End Product

Polymerization Techniques 1. Homogeneous systems 1.1. Bulk polymerization 1.2. Solution polymerization 2. Heterogeneous systems 2.1. Suspension polymerization 2.2. Emulsion polymerization 2.3. Precipitation polymerization 2.4. Polymerization in solid state 2.5. Polymerization in the gas phase Techniques

Advantages and Limitations Techniques

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

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 Casting formulations Low MW polymers for adhesives, plasticizers, tackifiers, and lubricant additives Techniques

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 Techniques

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

Solution Polymerization Techniques

Emulsion polymerization Emulsification Add emulsifying agent (e.g., soap or detergent) in an aqueous solution  to form micelles Monomers enter and swell the micelles Initiation Radicals (redox type) are generated in the aqueous phase and diffuse into micelles Propagation Polymerization propagated within micelles More monomers enter micelles to support the polymerization Termination 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) Techniques

Techniques

Stages of Particle Growth Three different stages Nucleation of particles Particle growth in presence of monomer droplets (3) Particle growth in absence of (Thoenes, 1991) Techniques

Emulsion Polymerization Recipe Water (continuous phase) Water-insoluble monomer Water-soluble initiator Surfactant Techniques 13

Emulsion Polymerization Recipe Techniques 14

Techniques

Techniques

Gas Phase Polymerization: Light olefins Fluidized bed polymerization Techniques

Hybrid Reactor for Polypropylene The process is a mass polymerization of propylene: 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 . 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. Techniques

End Techniques