Synthesis and Fractionation Studies of Functionalized Organosiloxanes

Abstract

The synthesis of difunctionalized aminopropyl-terminated poly-(dimethylsiloxane) via equilibrium polymerization of the cyclic tetramer in the presence of the functionalized disiloxane was demonstrated. The use of tetramethylammonium and tetrabutylphosphonium siloxanolate anionic catalysts for these reactions was studied. The reactions of the tetramethylammonium and tetrabutylphosphonium catalysts were limited to ~80 °C because of the known transience of these species at higher temperatures. The disappearance of the cyclic tetramer and disiloxane was monitored by HPLC (high-pressure liquid chromatographic) and GC (gas chromatographic) techniques, which indicated that the tetramethylammonium and tetrabutylphosphonium catalysts were much more efficient than the potassium catalyst, even when the potassium catalyst was used at much higher (e.g., 160 °C) temperatures. This behavior may be related to the higher degree of dissociation and, possibly, the enhanced solubility of the tetramethylammonium and tetrabutylphosphonium catalysts relative to the much more studied potassium catalyst. The number-average molecular weight was independent of the catalyst concentration and was influenced only by conversion and the molar ratio of the tetramer to the disiloxane. GPC (gel permeation chromatographic) characterization was also possible by derivatizing 1 Current address: 3M Center, St. Paul, MN 55144 2

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

“…On the other hand, for many applications of siloxane rubbers, a well-defined and complete cross-linking is often critical, since unconnected, dangling chains in the resulting networks would not perform as the load-bearing elements of structure. Often, polysiloxane precursors for such networks are synthesized by ring-opening polymerizations (ROPs) of cyclic siloxane monomers, conveniently using the so-called “transient catalysts” which can be decomposed after polymerization by heating to somewhat higher temperatures where decomposition products are easily eliminated from the reaction mixtures. ,, Among such “catalysts”, tetramethyl­ammonium silanolates (TMAS) (see Scheme ) have been found quite effective and practical, as either monofunctional or difunctional initiators, enabling the polymer growth to occur in either one or two linear directions. − For phenyl-substituted PDMSs, designed to eliminate crystallization, such ROPs, can be represented as shown in Scheme for an example of terpolymers containing dimethylsiloxy, −[Si­(CH 3 ) 2 O]–, DiMeS, diphenylsiloxy, −[SiPh 2 O]–, DiPhS, and methylvinylsiloxy, −[Si­(CH 3 )­(CHCH 2 )­O]–, MeViS, repeat units, where x , y , and z represent relative molar contents of the respective ones.…”

Viscosity–molecular weight relationship for aminopropyl‐terminated poly(dimethylsiloxane)

“…According to the method detailed by Geure et al,11 we synthesized ATPS samples by the tetramethylammonium siloxanolate12 catalyzed bulk equilibrium reaction of octamethylcyclotetrasiloxane (D 4 ) with a 1,3‐bis(3‐aminopropyl)‐1,1,3,3‐tetramethyldisiloxane (AT) end blocker. The equilibrium was maintained at 80°C for 24 h, and then the reaction temperature was increased to 150°C to decompose the catalyst.…”