n this lesson, we will consider what happens in terms of kinetics and skeletal structure when we polymerize two or more different monomers together to create a copolymer. We already learned in general what a copolymer is in Lesson 1 “what is a polymer?”. Make sure to refresh your memory on the difference between homopolymer and copolymer, and the definitions of alternating copolymer, block copolymer, random copolymer, and statistical copolymer.
Let’s consider a copolymer formed from reacting two monomers together. We consider a system in which the different monomers can react with each other, and they can also react with themselves. An example would be in the case of chain growth polymerization of two different monomers with vinyl groups. (This is an important point, because we saw some examples of step polymerization in which you could only get an alternating copolymer, RA2+RB2, just because of the specific functional groups that had to react. We are not considering that situation right now.) Consider the situation shown in Figure 8.1 where we have a purple and green monomer, and the purple happens to be incorporated faster into the polymer than the green one. Well, then at the start of our reaction, the polymer we form is going to contain mostly purple monomers. Later in the course of reaction, we find we have used up most of the purple monomers but have lots of green monomers left, so we begin to incorporate the green monomers more often than purple. As you can see, this leads to a distribution of the purple and green monomers along the polymer that is uneven; we have more repeat units of purple at one end of our polymer and more green at the other. You could also imagine that you stop the reaction before getting to a high extent of reaction, and end up with a polymer that has almost no green monomers at all! So what factors influence this distribution of purple and green along the length of the polymer? Can we predict and describe how various monomers will be incorporated when they are polymerized together?
