Synthesis and morphological behavior of silicon-containing triblock copolymers for nanostructure applications

We report the synthesis of high molecular weight triblock copolymers of the type ABA and BAB, where A is polyisoprene (PI) and B is poly(pentamethyldisilylstyrene) (P(PMDSS)), respectively. The volume fraction of the minority component (PI) for the ABA copolymer was 0.33, while that for the BAB copolymer was 0.23. The synthesis procedure of the P(PMDSS) blocks corresponded to that of polystyrene (PS), and low polydispersity with targeted compositions were achieved. The morphology of the triblock copolymers was characterized by transmission electron microscopy (TEM) and digital Fourier transform patterns. From TEM and diffraction analysis, the ABA polymer exhibited the double gyroid cubic morphology, while the BAB polymer showed a P(PMDSS) spherical domain morphology. The double gyroid morphology is the first to be reported in a silicon-containing block copolymer and consists of two three-dimensionally continuous, interpenetrating but nonintersecting networks of PI in a matrix of P(PMDSS)). Preliminary oxidative studies using ozone or O-2-RIE on the tricontinuous phase show that nanoporous structures can be generated.