Question

What property of an initiator will cause the polymer molecular weight to become broader?

Answer 1

Initiator, a source of any chemical species that reacts with a monomer (single molecule that can form chemical bonds) to form an intermediate compound capable of linking successively with a large number of other monomers into a polymeric compound.

The most widely used initiators produce free radicals (reactive atoms or groups of atoms that contain odd numbers of electrons); examples include peroxides and aliphatic azo compounds used to polymerize vinyl chloride, methyl methacrylate, and other monomers.

There are four industrial methods of radical polymerization:

• Bulk polymerization: reaction mixture contains only initiator and monomer, no solvent.
• Solution polymerization: reaction mixture contains solvent, initiator, and monomer.
• Suspension polymerization: reaction mixture contains an aqueous phase, water-insoluble monomer, and initiator soluble in the monomer droplets (both the monomer and the initiator are hydrophobic).
• Emulsion polymerization: similar to suspension polymerization except that the initiator is soluble in the aqueous phase rather than in the monomer droplets (the monomer is hydrophobic, and the initiator is hydrophilic). An emulsifying agent is also needed

The initiator should dissolve in the monomer. The reaction is initiated by heating or exposing to radiation. As the reaction proceeds the mixture becomes more viscous. The reaction is exothermic and a wide range of molecular masses are produced.