Cyclolinear polycarbosilanes - a recent addition to the class of organosilicon polymers

This article focuses on a relatively new group of organosilicon polymers known as cyclolinear polycarbosilanes (CLPCS). This group of polymers contains 1,3-disilacyclobutane (DSCB) rings, i.e., cyclo-{RSi(CH(2))(2)SiR}-, bridged by various linking groups, so as to form linear chains with regularly spaced, strained, rings that function as latent sites for cross-linking. This ring-chain, or "beads-on-a-string", type polymer has the general formula, [-{RSi(CH(2))(2)SiR}-Y-](n), where R and Y can be a variety of different groups, such as: R = -CH(3), -C(6)H(5) and -C(6)H(4)(CH(3)); Y = -(CH(2))(x)-, -C(6)H(4)-(CH[double bond, length as m-dash]CH)-C(6)H(4)-, and -C(6)H(4)-. Depending, in part, on the linking group, these CLPCS have been obtained by using two different synthesis methods, acyclic diene metathesis polymerization (ADMET) and Grignard coupling reactions. The resultant polymers exhibit a wide variation in physical properties, which depend on the nature of the silicon substituents, R, and the bridging group, Y. However, they also share some important characteristics, such as a relatively low glass transition temperature, amenability to the formation of thin films and coatings via spin-coating, and the tendency to undergo cross-linking on heating to 200-300 °C. The synthesis, characterization, and properties of these CLPCS are reviewed and their potential for application in such widely divergent areas as microelectronics processing (as low-k materials), protective, insulating coatings for Cu and other substrates, and photoluminescent films are described.