Synthesis and properties of isomeric poly(1-hydrido-1-trimethylsiloxy-tetramethyltrisiloxane) and poly(1-dimethylsiloxypentamethyltrisiloxane), regular polysiloxanes, that contain both Si-H and RSiO_(3/2) (T) units

摘要

Anionic ring-opening polymerization (AROP) of 1-dimethylsiloxypentamethylcyclotrisiloxane (I) catalyzed by butyllithium/HMPA gives poly(1-dimethylsiloxypentamethyltrisiloxane) (II). The isomeric polysiloxane, poly(1-hydrido-1-trimethylsiloxytetramethyltrisiloxane) (IV), has been prepared by AROP of 1-hydrido-1-trimethylsiloxytetramethylcyclotrisiloxane (III) catalyzed by dilithio diphenylsilanediolate. Both II and IV contain both Si-H and T groups. They have been characterized by ~1H, ~(13)C and ~(29)Si NMR as well as by IR spectroscopy. M_w/M_n determined by GPC is compared to M_n from ~1H NMR end group analysis. The microstructures of these has been determined by ~(29)Si NMR spectroscopy. Every third siloxane unit in these linear polymers is a RSiO_(3/2) (T) group.