Hexamethyltrisiloxane

Surprisingly, after this very first example, there was a 20 year delay in the literature in the appearance of the second report on siloxane macromonomers. However, during this period there have been numerous studies and developments in the vinyl and diene based macromonomers91 -94). The recent approach to the synthesis of siloxane macromonomers involves the lithiumtrimethylsilanolate initiated anionic polymerization of hexamethyltrisiloxane in THF 95,123). The living chain ends were then terminated by using styrene or methacrylate functional chlorosilanes as shown in Reaction Scheme X. 

Both PFS-PI and PFS-PDMS are synthesized by two-step anionic polymerization. The synthetic approach for the preparation of PFS-PDMS is shown in Scheme 1 [8,9] n-butyllithium was used to initiate the polymerization of the strained silicon-bridged ferrocenophane in THF solution, while the second block was built by the subsequent addition of hexamethyltrisiloxane (D3). The reaction was terminated with chlorotrimethylsilane. To obtain PFS-PI, the PI block was initiated with butyllithium, followed by the addition of the silicon-bridged ferrocenophane. 

A similar effect of ring size has been noted for the cyclic siloxanes88. The six-membered hexamethyltrisiloxane, (Me2SiO)3, has a 29Si chemical shift of —9.2 ppm. A shielding... 

The content and distribution of macrocyclics depend very much on monomer structure. Ethylene oxide exclusively gives a dimer (1,4-dioxane), while in other systems (e.g. 1,2-propylene oxide, epichlorohydrin, tert-butyl ethylene oxide) cyclic tetramers are predominant products 40. 1,3-Dioxolane or hexamethyltrisiloxane yield a complete sequence of cyclic oligomers, without any preference of a specific product51. 

Non-polymerizable 1,3-dioxane non-polymerizable Non-polymerizable Non-polymerizable Formation of cyclic dimer and Siloxanes 5) tetramer was reported 31 . Hexamethyltrisiloxane 1,3,5-tnoxane formation 32 331 of Considerable cyclization. Distribu- cyclic oligo- and polymers report- tion Gf cycjjc oligomers as predicted ed no quantitative data. by the J-S theory... 

The heats of polymerization of two cyclic siloxanes have been measured the six-membered ring, hexamethyltrisiloxane, and the five-membered paraffin-siloxane , 2,2,5,5-tetramethyl-l-oxa-2,5-disilacyclopentane (shown in Table 8.) For the corresponding cyclopentane the heat of polymerization is —5 2 kcal/mole, whilst for the paraffin-siloxane it is —10 0 kcal/mole. Thus, the effect of replacement of —(CHgla— by —Si(Mc2)—0—Si(Mc2)— in the cyclopentane molecule appears to either increase the ring strain in the monomer, or to stabilize the polymer, to the extent of some... 

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