Order−Disorder Phase Transition in Poly(di-n-butylstannane) Observed by UV−Vis and Raman Spectroscopy

Variable-temperature UV−vis and Raman spectra have enabled detection of a thermochromic phase transition for [ n Bu 2 Sn] n with an onset temperature T c at ca. 260 K. The exact T c value depends on the sample prehistory and the rate of cooling. This transition proceeds over a temperature interval from ca. 260 to ca. 200 K, when it reaches completion, and it involves two modifications: one with a disordered polymer backbone, which corresponds to a UV band at ca. 390 nm and a broad Raman feature for the ν(Sn−Sn) mode at ca. 120 cm -1, and a more ordered one (apparently, all-anti or transoid), to which a red-shifted UV band at ca. 420 nm and a very intense narrow Raman line for the ν(Sn−Sn) mode at ca. 145 cm -1 are assigned. No abrupt side chain ordering was observed at T c, but a gradual ordering, involving rotational isomerism about the C−C bonds, occurs on further lowering of the temperature. Comparison is made with data obtained for other polystannanes [ n R 2 Sn] n (R = n -hexyl, n -octyl).