Dependence of thermal properties on the copolymer sequence in diacetylene-containing polycarboranylenesiloxanes

Diacetylene-containing polycarboranylenesiloxane copolymers were prepared by two different methods to yield either alternating or block copolymers with respect to the diacetylene distribution along the backbone. With each method, a set of copolymers was prepared with trisiloxane:carborane:diacetylene molar ratios of 10:9:1, 5:4:1, and 3:2:1. Both sets of copolymers yielded networks upon thermal curing. Even though the two methods produced materials of comparable molecular weights and overall compositions, the variation in the copolymer sequence caused noticeable differences in the calorimetric glass transitions for the copolymers in which the diacetylene group was most concentrated (i.e., the 3:2:1 and 5:4:1 copolymers). The copolymers were characterized by differential scanning calorimetry, thermogravimetric analysis, and H-1 solid-state NMR spectroscopy.