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Controlled polymerization makes high-performance polysiloxanes

By Tetsuo Satoh |

Polysiloxanes are the main component of important industrial materials, such silicones and organosilicones. In recent years, demand has grown for higher-performance and higher-functionality of organosilicon materials, which require techniques that precisely control the structure of these materials. Although there are techniques capable of selectively forming one type of siloxane bond, such as the cross-condensation method, multistage synthesis has been necessary in order to obtain complex siloxane compounds.

Now, Keita Fuchise and colleagues at the Interdisciplinary Research Center for Catalytic Chemistry, National Institute of Advanced Industrial Science and Technology (IRC3, AIST, Tsukuba City, Japan; irc3.aist.go.jp) have developed a simple method for synthesizing polysiloxanes that have a well-controlled structure. With support from NEDO, the researchers developed a controlled, organo-catalytic living ring-opening polymerization of cyclotrisiloxanes. The reaction takes place at 30°C and uses water as an initiator and strong organic bases, such as amidinines, guanidines, phosphazene bases, and proazaphosphatrane, as catalysts. A variety of polysiloxanes can be produced with controlled number-average molecular weight (from 2.64 to 102.3 kg/mol), a narrow dispersity (D = 1.03–1.16) and well-defined structural symmetry.

The synthesis method is said to be very simple, and does not require a dewatering step due to the usage of water instead of lithium compounds as an initiator. By changing the ratio of cyclic trioxanes and water, the average molecular weight can be controlled to more than 100,000 (which corresponds to more than 1,350 Si–O units). The method can also be used for making block- and random-type copolymers. Structurally well-controlled polysiloxanes enables the development of silicone materials with higher performance and higher functionality, including longer life at high temperature, especially in the field of elastomers, gels, and surface-preparation and dispersing agents.

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