Polyhexylsilyne: Synthesis and properties of the first alkyl silicon network polymer.

The synthesis of polyhexylsilyne, [C sub 6 H sub (13) Si] sub n, 1, the first member of a new class of silicon network polymers, was accomplished using high intensity ultrasound to effect the reductive condensation of (hexyl) SiCl sub 3 with Na/K alloy under essentially homogeneous conditions. Purified 1 (- over M sub w ~ 24,000 versus polystyrene) was isolated as a moderately air and light sensitive yellow powder which remains soluble in hexanes, from which it is readily cast into transparent films. While the formula [SiR] sub n suggests an analogy to polyacetylenes, all chemical and spectral properties of polyhexylsilyne indicate that it exists as an amorphous network of tetrahedral alkylsilicon fragments. Solutions or films of 1 exhibit an intense absorption band ( lambda = 200 nm to 450 nm, epsilon at 200 nm = 29,000 per Si atom) associated with Si-Si sigma - conjugation. While UV irradiation of linear polysilanes results in rapid fragmentation, irradiation of 1 in air results in photooxidative crosslinking to form a siloxane network.