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I am having difficulty understanding (or at least need confirmation of my understanding) of this diagram regarding the formation of sidechains of polyethylene. If someone could explain it, that would be great :). Also, what do the rotation symbols mean? Below I include my understanding of the reaction.

polymerisation

My understanding is that the chain terminates with a carbon with an extra bond available. It covalently bonds to a hydrogen from back in the chain, thus forming a complete carbon (connected to the carbon before, and 3 hydrogens).

The group it stole the hydrogen from now becomes a carbon with a missing hydrogen, with an extra bond to fill. Therefore that carbon is connected to the carbons on the left and right of it, and missing one hydrogen on the side. Therefore the group should be CH, since it only has 1 hydrogen left after its other one was stolen. Why does the diagram say CH2?

Then, to the best of my understand, an ethylene group attaches to the side with the missing hydrogen, with the carbon filling the hydrogen's place. Thus the chain can be continued on the side, indefinitely. In option B: butyl side chain, the hydrogen from another part detaches and attaches to the open carbon on the side chain, terminating it, and forcing the original chain to continue.

In option A: what happens? I don't understand. Are the 2 ethyl side chains never ending? If so, how does that happen? How does the second side chain be produced?

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