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This is how the polymers are in coatings, they are units linked together to serve a purpose. And from the main page on coatings, the purpose is to protect and decorate. A general rule of thumb for coatings: the longer the chain is, the better the performance of the coating. So, you wonder, how you get those long chains? Simply, it is chemistry. Is it that simple, no, but chemical reactions make these polymers. There are 2 broad types of polymers you can make, or synthesize: thermoplastics and thermosets. Thermoplastics are by definition polymers that soften and flow when heated. These polymers can be heated and reformed. This is because the polymer chains are not crosslinked, or connected. These thermoplastic polymer chains are like pieces of spaghetti that can slide by each other and are not connected. The sliding around of these polymer chains is what allows thermoplastics to flow when heated. The colorful figure above shows five unlinked polymer chains. Thermosets, on the other hand, will not flow when heated. This is because they are crosslinked or connected together, like a net. Below is a depiction of a thermoset polymer:
Now you may ask how do I make a thermoplastic polymer and how do I make a thermoset polymer. Well, to make it simple, thermoplastic polymers can only be connected on two sides. Below is a cartoon replica that show how the polymer chains are connected. Thermoplastic polymers are made by connecting the units at the ends. The blue circles indicate where these units can be connected. When these blue circles are connected you make a long straight polymers. In chemical terms these blue circles indicate functional sites. With only two functional sites one would make a thermoplastic polymer.
this
is a single unit that makes up the polymer chain.
When the single units are linked at the blue circles you have a straight,
or linear polymer. A thermoplastic.
In order to make a thermoset polymer your units will have a little twist to them. Most of the units will be like the ones above, however there is a small amount of other units that look a little different. These new units have more than 2 functional sites. These extra sites allow for the polymer chains to becomes connected like a net, forming crosslinks. Below are cartoon replicas of polymer units that have 3 and 4 functional sites.
or 
With in the broad categories of thermoplastics and thermosets
are the different types of polymers themselves. The major polymer
types used in coatings today are polyesters, polyurethanes, epoxy polymers,
and polyacrylates. Below are links to each of the polymer types I
just mentioned.
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