0000000000704142
AUTHOR
Mario Müller
Influence of hydrogen bonding on the viscoelastic properties of thermoreversible networks: analysis of the local complex dynamics
Abstract The viscoelastic properties of thermoreversible polybutadiene networks in which junctions are formed by binary contacts between polar stickers (phenylurazole) are investigated by a dynamic mechanical spectroscopy within the frequency range 0.0079–79.5 Hz (0.05–500 rads−1). Time-temperature superposition is applicable in the terminal flow region and the glass transition regime, whereas thermorheologically complex behaviour is observed within the rubbery plateau region. For the terminal relaxation zone the polar stickers enhance the relaxation time and broaden the relaxation time spectrum. The thermorheologically complex behaviour within the rubbery plateau region results from the oc…
The molecular dynamics of thermoreversible networks as studied by broadband dielectric spectroscopy
Polybutadienes modified by a small number of 4-phenyl-1,2,4-triazoline-3,5-dione form thermoreversible networks via hydrogen bonding between the polar stickers. The molecular dynamics of systems with different contents of polar stickers are investigated by broadband dielectric spectroscopy in the frequency regime of 10−1–109 Hz. Unmodified polybutadiene shows two relaxation processes, the α-relaxation which is correlated to the dynamic glass transition of the polybutadiene, and a β-relaxation corresponding to a local relaxation of polybutadiene segments. In the polar functionalized systems, besides these two relaxations, an additional relaxation process (called α*) is observed, which occurs…
Sequence and analysis of chromosome 4 of the plant Arabidopsis thaliana
The higher plant Arabidopsis thaliana (Arabidopsis) is an important model for identifying plant genes and determining their function. To assist biological investigations and to define chromosome structure, a coordinated effort to sequence the Arabidopsis genome was initiated in late 1996. Here we report one of the first milestones of this project, the sequence of chromosome 4. Analysis of 17.38 megabases of unique sequence, representing about 17% of the genome, reveals 3,744 protein coding genes, 81 transfer RNAs and numerous repeat elements. Heterochromatic regions surrounding the putative centromere, which has not yet been completely sequenced, are characterized by an increased frequency …