Anionic polymerization of 2,2,5,5‐tetramethyl‐1‐oxa‐2,5‐disilacyclopentane

Abstract

In the first of a two‐part series, a study has been made of the anionic polymerization of a five‐membered cyclocarbosiloxane, 2,2,5,5‐tetramethyl‐1‐oxa‐2,5‐disilacyclopentane. The polymerization was initiated by lithium n‐butyldiphenylsilanolate in the presence of tetrahydrofuran. The chemical shifts of the protons of the cyclic monomer and the polymer were found to be different, and therefore the rate of polymerization was obtained in an NMR spectrometer. The effects of varying the concentrations of THF, initiator, and water upon the rate of polymerization and upon the molecular weight and the molecular weight distribution were investigated. At a constant concentration of monomer and initiator, the rate of polymerization increased when the THF concentration was increased. At a constant concentration of monomer and THF the rate of polymerization reached a constant value when the initiator concentration was varied. The molecular weight and the molecular weight distribution were dependent upon the initiator to water ratio, whereas water concentration had little effect on the rate of polymerization. Essentially monodispersed polymers were obtained when the concentration of initiator was in large excess to that of water or vice versa. A bimodal distribution in molecular weight was obtained when the concentration of initiator was approximately equal to that of water. The apparent activation energy of polymerization was 12.7 kcal/mole.

Phenylene‐Bridged Cyclic Siloxanes as Precursors to Nonshrinking Sol–Gel Systems and Their Use as Encapsulants

“…We showed previously that ROP of neat monomer 2 is accompanied by a shrinkage of less than 5 %. [5] Likewise, ROP of 3 results in a similar loss of volume during the ROP reaction. Despite the structural similarity of 3 and 4, disilaoxacyclopentene 4, and the disilaindoles 5 and 6, [6] do not undergo ROP with a variety of anionic catalysts and reaction conditions.…”

“…[9] The dinuclear helicate A2 was formed in the presence of lithium, sodium, potassium as well as many other countercations. [10] For entropic reasons the formation of the dinuclear complexes A and B should be favored over the oligonuclear species C and D. [5] However, the binding of the countercations to the anionic coordination compounds either stabilizes the dinuclear complexes or destabilizes them leading to the formation of the oligomers C or D. [9,11] A red soluble solid is obtained when a 1:1 mixture of 1-H 4 and 2-H 4 with Ti(OMe) 4 (methanol, reflux or (acac) 2 TiO, methanol, room temperature) is treated with potassium carbonate as base and the solvent is removed. ).…”

“…[4] On the other hand, Raymond et al performed a study in which the self-recognition during the self-assembly of triple-stranded homoleptic helicates from a mixture of ligands is based on the length of different rigid spacers which bridge two catecholamide moieties. [5] Self-recognition also can be controlled by the chirality of the organic ligands. [6,7] Herein we describe investigations on the self-recognition of alkyl-bridged bis-(catechol) ligands 1-H 4 and 2-H 4 on the formation of a mixture of dinuclear titanium(iv) complexes.…”

Approaches to polymers containing a silicon-oxygen bond in the main chain

“…Piccoli et al first reported the anionic ROP of methyl-and/ or phenyl-substituted five-membered cyclocarbodisiloxanes and obtained high-molecular-weight polymers in 1960 [76]. Later investigations on the polymerization of these compounds have shown that this is a very efficient way to prepare poly(carbosiloxane)s of high molecular weight (M n = ∼130 000) and relatively narrow molecular weight distribution (M w /M n = 1.28-1.66) [77][78][79].…”

“…On the other hand, relatively less attention has been paid to the synthesis of poly(carbosiloxane)s from cyclic carbodisiloxanes [76][77][78][79][80][81][82]. Piccoli et al first reported the anionic ROP of methyl-and/ or phenyl-substituted five-membered cyclocarbodisiloxanes and obtained high-molecular-weight polymers in 1960 [76].…”