Past exam of the chemistry B course of the University of Cambridge / 2023 / Paper 2 / B9 / b / ii / Solution

R${}_3$SiCl acts as a monofunctional chain termination reagent. hydrolysis gives R${}_3$SiOH, which forms a terminal R${}_3$Si–O unit but cannot continue growth through a second silanol group. Increasing its proportion therefore increases the number of capped ends and lowers the attainable average chain length. The resulting material generally has lower viscosity and less chain entanglement, rather than acquiring a cross-linked network merely from end-capping.