Polymer Architecture Latex Binders

It’s convenient to think of polymers as long chains, and, sometimes, that’s accurate. But polymers have a number of complex interactions — between monomers and between polymer chains — that result in recognizable architectures. These architectures can have tremendous impact on the properties of a polymer emulsion being developed.

Imagine for a moment that you and 19 of your friends gather outside in a large open field. Now imagine that you link your left hand in the belt loop of the next person and that she does the same and so on, until all 20 of you are linked together in a chain. Next, another group of 20 people comes out to join the first. They also link together, left hand looped through the belt loop of the adjacent person and so on, until a second chain is formed. Now try to picture those two chains of people moving next to each other. The two chains behave independently, sliding back and forth in opposite directions.

Finally, imagine that all of the free right hands of one chain grasp the free right hands of the other chain. The two chains of people are now connected, and this changes how the chains behave. They can still move side-to-side but only in a very limited way. The overall properties of the system — defined by the two interacting chains — is changed.

This example illustrates one of the most important concepts in polymer chemistry — polymer architecture. In this article, we’ll take a closer look at the various types of architectures and how modifying the basic structure of emulsion polymers changes their properties.

In the thought experiment described above, you and your friends represented monomers, the building blocks of a polymer chain. Of course, real-life monomers are molecules with specific chemical makeups. A few common monomers include ethylene (C₂H₄), styrene (C₈H₈), and vinyl chloride (C₂H₃Cl). Each of these monomers has unique properties when they exist by themselves.

Monomers aren’t generally useful in their pure form, but as building blocks for other materials, they are quite important. Polymerization is the process that connects the building blocks together into longer chains. Consider polystyrene, which is made by joining styrene molecules together to form a long carbon backbone. A long chain of polystyrene is one of the most common polymers on the planet, and it has properties that are different than styrene. The monomer styrene is a colorless oily liquid that evaporates easily and has a sweet smell at low concentrations, but polystyrene is a hard, solid plastic that is often used in products such as food packaging and laboratory ware.

Polystyrene won’t form spontaneously. The polymerization of polystyrene, known as chain or radical chain polymerization, begins when an initiator is decomposed to yield free radicals. These free radicals — highly reactive chemical species — then attack the styrene monomer, adding to one of the electrons of a double bond and releasing the remaining electron of the bond. Then, the monomer itself becomes a free radical that can react with a neighboring styrene molecule. This happens over and over again — a process called propagation — until a long chain is formed.

Just as the growth of a polymer chain can be initiated, then it can also be interrupted. There are a number of ways to stop polymerization, a process known as termination. For example, termination by combination occurs when two independently propagating chains meet at their chemically active ends; they join together and, without any free electrons available to offer a monomer, the resulting chain stops growing.

A chemist has many options available for controlling the final polymer and its properties. He can manipulate any of the following:

1. The choice of the monomer
2. The way in which monomers stitch together
3. The length of the polymer chain
4. The way two polymer chains interact

Thanks & Best regards,

      Lin Yang(Ms.)

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