Telomerization is a chemical process that creates short chain polymers, called oligomers, consisting of two to ten repeating units. Oligomers are mixed in with polymers of the same type to increase a material’s flexibility and workability. The polymerization reaction is cut short in chain transfer polymer reactions by the telomerization process.
Polymerization reactions usually happen quite quickly. The monomer is the basic single unit that forms the backbone of the polymer. Usually, the monomer units must be coaxed to react by either adding a catalyst or energy. The polymerization reaction will happen almost instantaneously once the activation energy, or the energy hurdle that prevents spontaneous reaction, is met.
The reaction, although proceeding rapidly, adds monomers to the chain one at a time. The polymer chains keep growing until the monomer is exhausted. The final molecular weight of the polymer is controlled by how many chains are initiated, a function of the initial conditions. The initial conditions would include the amount of catalyst, the heat added, and the reactor design.
Polymers, because of their high molecular weight, tend to be stiff. In order to make the material more pliable, short chain oligomers of the same or similar chemical composition are added. The common new-car smell is caused by migration of the oligomers, called plasticizers in this context, out of vinyl upholstery. The oligomers are short enough to have some volatility, allowing them to be detected by the nose.
There are many kinds of polymer reactions. In a chain transfer reaction, the reactive species is a free radical, an unstable molecular species with an unpaired electron that will react immediately. The chain propagation steps of the polymer reaction keep the radical moving along the chain as it grows.
Access to the reactive radical end gets more difficult as the chain gets longer. If a chain transfer agent is present, the agent will transfer the free radical to a new monomer and terminate the chain. The free radical monomer will start a new chain. Both the termination of the early chain, which is the telomerization step, and the initiation of a new chain work to limit the length of the chains.
Good chain transfer agents usually have one weak chemical bond, facilitating the transfer of the unpaired electron. Common agents in use are halocarbons, carbons bonded to the halogen series of elements. Thiols, the sulfur equivalent of an alcohol with a sulfur-hydrogen (—SH) functional group, are also used.
Short chain oligomers can undergo telomerization with each other in four configurations: head to head, head to tail, tail to tail, and tail to head. The oligomer mixture will consist of all four molecules. Polymer chemists study ways to make telomerization results more predictable.
