An active center is created in the second step of initiation, when a free radical generated from the initiation system attacks the -bond of a monomer molecule, and two modes of addition are possible. Complete the two reactions between the free radical and the monomer shown below (i.e., write down the structure of the product for each reaction).

a. Head-to-tail: + CH=CH2 b. Head-to-head: + CH=CH2 =