Cyclic poly(dimethylsiloxane) via ring-closing dehydrocoupling of α,ω-dihydroxy-PDMS with α,ω-dihydrido-PDMS in dilute solution

Cyclic poly(dimethylsiloxane) (PDMS) was prepared from commercially available linear α,ω-dihydroxy-PDMS by a platinum-catalyzed dehydrocoupling of its chain ends with α,ω-dihydrido-PDMS in dilute solution. Ring closing was verified by MALDI-ToF mass spectrometry along with GPC, IR, ¹H and ²⁹Si NMR spectroscopy. Purification of the cyclic PDMS was achieved by inclusion complexation of linear byproducts with γ-cyclodextrin. Cyclic yields are≥50% and the average molecular weight (M) closely reflects that of the linear starting material. Yields of large cycles, [(CH₃)₂SiO]_x where x>6, are greater than those achieved by the traditional ring-chain equilibration route beginning with [(CH₃)₂SiO]₄ and [(CH₃)₂SiO]₅ [1], and the M is greater than that obtained for the cyclic product obtained from base-catalyzed cyclodepolymerization of the same α,ω-dihydroxy-PDMS precursor [2].