UV and Raman study of thermochromic phase transition in poly(di-n-hexylgermane)

The thermochromic phase transition of poly(di-n-hexylgermane) (1) was reinv estgated using low-molecular-weight (lmw) and high-molecular-weight (hmw) p olymer samples. The equilibrium phase transition temperature T-c of 1, dete rmined by variable temperature Raman and UV spectroscopy as well as by DSC, was found to lie not in the interval from + 15 to - 10 degreesC, as was re ported previously, but in the region 45-55 degreesC, that is, very close to T-c of the Si and Sn analogues. Thus, the phase behaviour of the polymetal lanes [(n)Hex(2)M](w) M = Si, Ge, Sri is governed not by the nature of the main chain but by intermolecular interactions of the substituent groups. Th e nature of the order-disorder phase transition of 1 depends on the polymer molecular weight and the sample thermal history. Above T-c hmw polymer 1 e xists as hexagonal columnar mesophase while hmw 1 is in amorphous state, bo th with disordered backbone. On cooling to room temperature, hmw polymer tr ansforms to a crystalline modification with an all-anti conformation of the backbone and ordered hexyl groups, whereas the process of ordering of the main chain for lmw, sample is more complicated. (C) 2001 Elsevier Science B .V. All rights reserved.