When Attempting Chain Extension, Even Without Solvent, It Is Not Possible to Avoid Chojnowski Metathesis Giving D.

A simple, mild and efficient method to prepare HSi- or HOSi-telechelic, high-molecular-weight polydimethylsiloxane polymers (to 41,600 g·mol) using the one-shot hydrolysis of MM is reported; titration of the water allowed for higher molecular weights (to 153,900 g·mol). The "living" character of the chain extension processes was demonstrated by adding a small portion of MM and B(CF) (BCF) to a first formed polymer, which led to a ~2-fold, second growth in molecular weight. The heterogeneous reaction reached completion in less than 30 min, much less in some cases, regardless of whether it was performed neat or 50 wt% in dry toluene; homogeneous reactions in toluene were much slower. The process does not involve traditional redistribution, as judged by the low quantities (<3%) of D produced. However, it is not possible to avoid Chojnowski metathesis from MDDM giving D, which occurs competitively with chain extension.