Use of polyiminophosphazene bases for ring‐opening polymerizations

Abstract

The polyiminophosphazene bases Et‐P2 and t‐Bu‐P4 were used as a promoter for ethylene oxide and siloxane polymerizations. Initiation by an alcohol in combination with t‐Bu‐P4 lead to an extremely rapid polymerization reaction of octamethylcyclotetrasiloxane. In the case of ethylene oxide, well‐defined polymers were obtained, however the rate of polymerization decreased during the polymerization reaction due to decomposition of the counterion. In combination with organolithium compounds, the phosphazene bases lead to well‐defined polymers in the case of cyclotrisiloxanes as well as in the case of ethylene oxide.

Metal‐Free Activation in the Anionic Ring‐Opening Polymerization of Cyclopropane Derivatives

“…The substantial increase in temperature needed to obtain the same order of magnitude for k p (2.0 Â 10 À4 and 5.8 Â 10 À4 L Á mol À1 Á s À1 for polymerizations initiated by sodium thiophenolate at 130 8C in DMSO and by the phosphazene/thiophenol system at 60 8C in THF, respectively) clearly demonstrate a higher reactivity of this new initiating system compared to the conventional one. A similar increase in reactivity with phosphazene bases has been already observed for the ROP of cyclic esters, [12] cyclosiloxanes, [8] and ethylene oxide. [8,9] It is now well accepted that the use of a very soft and bulky cation such as [Bu…”

“…A similar increase in reactivity with phosphazene bases has been already observed for the ROP of cyclic esters, [12] cyclosiloxanes, [8] and ethylene oxide. [8,9] It is now well accepted that the use of a very soft and bulky cation such as [Bu…”

“…By analogy with ethylene oxide polymerization, [8,9] one can postulate that Bu t P 4 acts as a deprotonating agent and activates the thiophenol for the nucleophilic attack on the cyclopropane ring. Propagation occurs through the malonate carbanion as previously established for the polymerization of cyclopropane-1,1-dicarboxylates initiated with sodium thiophenolate (Scheme 1).…”

“…[6] It can be used as an activating ligand for metallic cations involved as counter-ions in anionic polymerizations. [7] In association with an alcohol, it has been used to initiate the polymerization of ethylene oxide, [8,9] cyclosiloxanes, [8,10,11] and cyclic esters. [12] The very soft large counter-ion formed by deprotonation of the alcohol (methanol or 1-pyrene butanol) involves a fast ROP of those monomers.…”

Anionic Polymerization of Ethylene Oxide in the Presence of the Phosphazene Base ButP4 – Kinetic Investigations Using In‐Situ FT‐NIR Spectroscopy and MALDI‐ToF MS

“…[12] Recently Eßwein et al showed that in the presence of a strong Lewis base, for example, the phosphazene base Bu t P 4 , polymerization of ethylene oxide with Li þ counterions can be achieved. [13][14][15] In this case the phosphazene base Bu t P 4 forms a strong complex with Li þ resulting in a break up of the strong lithium alkoxide aggregates, and thus making the polymerization of ethylene oxide possible. Furthermore, because of the strongly basic character of the phosphazene base Bu t P 4 even alcohols can be used as initiators.…”