The effects of substituents on the reactivity of organocyclosiloxanes in anionic polymerization

Ring-Opening Polymerization (ROP) and Catalytic Rearrangement as a Way to Obtain Siloxane Mono- and Telechelics, as Well as Well-Organized Branching Centers: History and Prospects

“…The next factor that has a significant effect on the course of polymerization is the nature of the organic groups at the silicon atoms of siloxane cyclosiloxanes. The introduction of electron-donating substituents-longer hydrocarbons than the methyl group-reduces the rate of anionic polymerization of cyclosiloxane, while electron-withdrawing substituentsalkenyl, aromatic, phenyl, 3,3,3-trifluoropropyl or cyanoalkyl groups-increase the rate of polymerization [82][83][84]. In this case, electron-withdrawing substituents at the silicon atom during anionic polymerization lead to the formation of a siloxanolate anion with a lower nucleophilic activity, which somewhat levels out the increase in the activity of cycles during polymerization.…”

Suppression of Crystallization in Polydimethylsiloxanes and Chain Branching in Their Phenyl-Containing Copolymers

“…−125 °C, while its closest relative, polydiethyl­siloxane, PDES, −[Si­(CH 2 CH 3 ) 2 O] n –, has the lowest T g of all polymers known of around −140 °C. − As a consequence, polysiloxanes are excellent precursors for exceptional low-temperature elastomers, with a major deficiency resulting from their unfavorable crystallization behavior, since PDMS is prone to crystallization at ca. −40 to −50 °C, − while PDES shows several different solid state transitions starting at as low as −70 °C. − In both cases, these transitions limit the low-temperature usefulness of their elastomers to about 10 °C above the highest temperature transition, and it is therefore highly desirable to suppress crystallization in order to extend elastomeric properties of the resulting rubbers to well below these temperatures. Toward this end, it has been well documented that complete prevention of crystallization in linear PDMSs can be achieved by incorporating small amounts (often less than 5 mol %) of crystallization disruptors, such as large and bulky phenyl units, into the polymer side groups. ,,− …”

Anionic non‐equilibrium ring‐opening polymerization of octamethylcyclotetrasiloxane (D4) initiated by silazyl‐lithiums

“…It can be concluded that the initiation activity was affected by both the steric hindrance effect and the electronic effect. For these substituents, the order of steric hindrance was Me < Vi < Ph and the order of electron‐withdrawing ability was Ph > Vi > Me9. When the substituent was an electron‐withdrawing group, the electron atmosphere of NLi would be withdrawn to atom N and the metal counterion (Li + ) could combine with the promoter more easily.…”