Telomerization creates short-chain polymers called oligomers, which are mixed with polymers to increase flexibility. Polymerization reactions add monomers one at a time until depleted, and oligomers are added to make materials more ductile. Chain transfer agents limit chain length and can be halocarbons or thiols. Short-chain oligomers can undergo telomerization in four configurations. Polymer chemists are studying ways to make telomerization more predictable.
Telomerization is a chemical process that creates short-chain polymers, called oligomers, made up of two to ten repeating units. Oligomers are mixed with polymers of the same type to increase the flexibility and processability of a material. The polymerization reaction is stopped in chain transfer polymer reactions by the telomerization process.
Polymerization reactions usually occur quite rapidly. The monomer is the single basic unit that forms the backbone of the polymer. Usually, the monomer units have to be coaxed to react by adding a catalyst or energy. The polymerization reaction will occur almost instantaneously once the activation energy, or energy barrier preventing the spontaneous reaction, is reached.
The reaction, while proceeding rapidly, adds monomers to the chain one at a time. The polymer chains continue to grow until the monomer is depleted. The final molecular weight of the polymer is controlled by how many chains are started, a function of the initial conditions. Initial conditions would include the amount of catalyst, heat added, and reactor design.
Polymers, due to their high molecular weight, tend to be stiff. To make the material more ductile, short-chain oligomers of the same or similar chemical composition are added. The common new car odor is caused by the migration of oligomers, called plasticizers in this context, from the vinyl upholstery. Oligomers are short enough to have some volatility, allowing them to be detected by the nose.
There are many types 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.
Accessing the radical reactive end becomes more difficult as the chain lengthens. 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 initial chain, which is the telomerization phase, and the initiation of a new chain contribute to limiting the length of the chains.
Good chain transfer agents usually have a weak chemical bond, facilitating the transfer of the unpaired electron. The common agents in use are halocarbons, carbons bonded to the halogen series of elements. Also used are thiols, the sulfur equivalent of an alcohol with a sulfur-hydrogen (-SH) functional group.
Short-chain oligomers can undergo telomerization with each other in four configurations: butt, butt, tail-to-tail, and tail-to-butt. The oligomer mixture will consist of all four molecules. Polymer chemists are studying ways to make telomerization results more predictable.
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