ISSN:
1572-8870
Schlagwort(e):
Polysilenes
;
polysilanes
;
liquid crystals
;
mesophases
;
birefringence
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Chemie und Pharmazie
Notizen:
Abstract (I) Ordered and disordered polysilane copolymers: Condensation of ClSiMe2Si(n-Hex)2SiMe2Cl with Na/K in toluene at 90°C produced a polymer with a strongly bimodal molecular weight distribution. The high-M w and low-M w portions were separated by fractional precipitation with 2-propanol, and the properties of the two fractions were investigated.29Si-NMR spectra show that the low-M w fraction is fully ordered but the high-M w fraction is randomized. (II) Liquid crystalline polysilanes: Condensation ofn-Bu(n-Hex)SiCl2 with Na in toluene led to a homopolymer which is a rubbery solid at 25°C. The polymer undergoes a second-order transition at −45°C and a first-order (melt) transition at −20°C. X-ray diffraction shows that the polymer has the same structure, a columnar hexagonal lattice, in all three phases; from −20 to 〉200°C, it exists in a columnar liquid crystalline mesophase. Similar hexagonal mesophases were observed at 25°C for the family of copolymers, (n-Hex2Si) n (Alk2Si) m , Alk =n-Pentyl,n-Bu,n-Pr, Et, Me.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/BF00696534
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