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  • 1990-1994  (3)
  • mesophases  (2)
  • Arousal  (1)
  • Bissilylamines
  • 1
    Electronic Resource
    Electronic Resource
    Some recent developments in polysilane chemistry (1992)
    Springer
    Journal of inorganic and organometallic polymers and materials 2 (1992), S. 29-45 
    Details
    ISSN: 1572-8870
    Keywords: Polysilenes ; polysilanes ; liquid crystals ; mesophases ; birefringence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00696534
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  • 2
    Electronic Resource
    Electronic Resource
    Ethynylene-disilanylene copolymers (1991)
    Springer
    Journal of inorganic and organometallic polymers and materials 1 (1991), S. 545-565 
    Details
    ISSN: 1572-8870
    Keywords: Polysilanes ; sigma-pi conjugation ; mesophases ; polymer crystals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Polymers of structure (SiR2SiR2-C ≡ C-SiR2′SiR2′-C ≡ C) n , in which ethynylene units alternate with disilylene units, have been prepared by two routes: (a) condensation of dichlorodisilanes with dilithium derivatives of 1,2-diethynyldisilanes and (b) ring-opening polymerization of strained cyclic disilanylene-acetylnes, (SiR2SiR2C ≡ C)2. The polymers display UV absorption near 240 nm indicative of σ − π conjugation between the Si2 and the C ≡ C moieties. Polymers with R=R′=n-Bu or R=n-Bu, R′=Ph, undergo solid-state transitions to form liquid crystalline mesophases resembling those observed for many poly(silylenes). Single crystals were obtained for the polymer with R=R′=CH3, by precipitation from dilute cyclohexane solution. The solid-state properties and structures of this family of polymers are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00683516
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Function of cigarette smoking in relation to examinations (1992)
    Springer
    Psychopharmacology 108 (1992), S. 456-459 
    Details
    ISSN: 1432-2072
    Keywords: Smoking ; Nicotine ; Examination anxiety ; Stress ; Arousal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Eighty-two college students took part in a study on motives underlying increases in cigarette smoking prior to examinations. One group was tested a month before, and a second group was tested the day before, the start of examinations. Measures were taken of current cigarette consumption, general anxiety, anxiety about forthcoming exams, the importance of sedative and stimulant smoking motives, hours spent revising and in other activities and amount smoked during these activities. The results indicated that the students increased the hours they spent revising and there was a corresponding increase in the number of cigarettes smoked during this activity. They also reported an increase in the importance of stimulant smoking motives. Anxiety levels increased in the run up to exams but there was no increase in sedative smoking motives. The results raise the issue of whether any anxiolytic action of nicotine may be limited to acute stressors and also whether smokers' use of cigarettes to help them stay alert during revision translates into improved examination performance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02247421
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    Paper (German National Licenses)
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