Siiloxane polymer experiment I believe the first reaction would be a substitution of $\ce{SiMe3}$ for $\ce{I}$ and creating $\ce{SiMe3Cl}$.
The second process I think would involve the $\ce{Mg}$ removing the two $\ce{Cl}$ and forming diphenylsilane, which would likely be a repeating unit in a silicone polymer.
Could any explain the mechanism for these reactions?
A)SiMe3 Increases the inductivity and reduces Aromaticity,
so by free radical (uv termination) its likely to have p-iodideSi(Me)3Bencene.

B)Dimer crystal solution in Cl- ions.  (Ph)2Si(Cl)Mg+---ClSi(Ph)2
Or Solid crystals of (Ph)2Si(Cl)MgCl.