For radical polymerization reactions, azobis(isobutyronitrile) (AIBN) can also be used as a radical initiator

Draw the mechanism of radical formation if you know that N2 is formed as a by-product.


[![enter image description here](https://i.stack.imgur.com/p5B8I.png)](https://i.stack.imgur.com/p5B8I.png)


The solution they give us is


[![enter image description here](https://i.stack.imgur.com/DqcfO.png)](https://i.stack.imgur.com/DqcfO.png)


I know what radical polymerization is. The free electron of a molecule binds with another molecule and creates a link. The second molecule will then have a free electron that will again bind with a third molecule. And this reaction will repeat.


But I'm a bit confused by their solution. How can I guess that N2 will form as a byproduct if they didn't tell us directly ? Also, do I understand correctly that a third electron link will be created with the two electrons that were previously bonded to the carbon atom ? At the end, we have N2 and the molecule in the second picture with a free electron. Do I understand correctly that when a molecule has a free electron like this, it is now a radical initiator ? So this molecule can later be used to start a polymerization process ?


I hope my question is clear. I'm a bit confused by those terms and would really appreciate your help. Thank you so much !


