Reaction between RCH2=CH2 and CCl4 -- Why does it form RCHClCH2CH(R)CH2CCl3 along with RCHClCH2CCl3? I am reading Organic Chemistry from Morrison &amp; Boyd and there is this problem in it:


  Problem 6.8 From the addition of $\ce{CCl4}$ to alkenes (in presence of peroxides), $\ce{RCH2=CH2}$, there is obtained not only $\ce{RCHClCH2CCl3}$ but also $\ce{RCHClCH2CH(R)CH2CCl3}.$ Using only the kind of reactions you have already encountered, suggest a mechanism for formation of this second product.


I know that the addition of CCl4 to alkenes in presence of peroxides is a free radical reaction. So what I have thought is, while the reaction is going on, there are the following species present: RCH=CH2 (reactant), RC^HCH2CCl3 (^ represents the electron on the free radical) and the product $\ce{RCHClCH2CCl3}$.

When the free radical reacts with $\ce{RCH=CH2}$ it gives the main product $\ce{RCHClCH2CCl3}$ and $\ce{.CCl3}$. So probably the second product is formed by reaction of $\ce{.CH(R)CH2CCl3}$ with $\ce{RCHClCH2CCl3}$? 

$$\ce{RCHClCH2-CCl3 + .CH(R)CH2CCl3 -&gt;[???] RCHClCH2CH(R)CH2CCl3 + .CCl3}$$

However this reaction I have never encountered while the question explicitly states that I have to use only the kind of reactions I have already encountered. I don't think anyway that this reaction is possible.

There must be something big that I am missing here ... Can someone give me a little hint?
The propagation series starts with the addition of the trichloromethyl radical to the alkene to give the more stable secondary radical. This radical can abstract a chloride from carbon tetrachloride to give the expected product. Alternatively, this radical can add to the alkene to give an a new carbon-centered radical with an extended chain. Abstraction of chloride gives the 'unexpected' product.



The key realization here, as permeakra suggested in the comments, is that any radical in solution can theoretically add to the alkene. This means that the penultimate radical intermediate could add to the alkene as well extending the chain. This is the basis of a radical polymerization.