where .............. represents the main chain.
The Me3SiOK formed will attack another chain to reduce the
average molecular weight of the linear polymer formed.
The copolymerization of (Me2SiO)4 in the presence of
Me3SiOSiMe3 with Me4NOH as catalyst displays a surprising
viscosity change over time (Noll, 1968). First a peak or
viscosity maximum is observed at the beginning of the reaction.
The presence of two oxygen atoms on each silicon in the
cyclics makes them more susceptible to a nucleophilic attack
by the base catalyst than the silicon of the endblocker, which is
substituted by only one oxygen atom. The cyclics are polymerized
first into very long, viscous chains that are subsequently
reduced in length by the addition of terminal groups provided
by the endblocker, which is slower to react. This reaction can
be described as follows: