INTRAMOLECULAR ORDERING STOPPED BY GLASSIFICATION - 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 o f PBHS which begins at ca.-25-degrees-C consists of a gradual transfor mation on cooling of a disordered macromolecule main chain into more o rdered, probably helical conformation and then into an all-trans confo rmation with accompanying crystallization. The polarizability-driven t ransition from the helical to the all-trans conformation does not proc eed to completion, but ceases at ca.-60-degrees-C due to a quasi-secon d-order phase transition of a glassification type which ''freezes out' ' some thermal molecular motions necessary for this transformation to occur. Even at -240-degrees-C the polymer exists as a mixture of two f orms.