Intramolecular Ordering Stopped by Classification. A UV and Raman Study of Poly[n-butyl-n-hexylsilylene] Phase Transitions

UV and Raman data show that a prolonged first-order phase transition of PBHS which begins at ca. –25 °C consists of a gradual transformation on cooling of a disordered macromolecule main chain into more ordered, probably helical conformation and then into an all-trans conformation with accompanying crystallization. The polarizability-driven transition from the helical to the all-trans conformation does not proceed to completion, but ceases at ca. –60 °C due to a quasi-second-order phase transition of a glassification type which “freezes out” some thermal molecular motions necessary for this transformation to occur. Even at –240 °C the polymer exists as a mixture of two forms.