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B Units (b + unit)

Distribution by Scientific Domains

Polymers and Materials Science	80%

Selected Abstracts

Thiophene,Benzothiadiazole Co-Oligomers: Synthesis, Optoelectronic Properties, Electrical Characterization, and Thin-Film Patterning

ADVANCED FUNCTIONAL MATERIALS, Issue 3 2010
Manuela Melucci
Abstract Newly synthesized thiophene (T) and benzothiadiazole (B) co-oligomers of different size, alternation motifs, and alkyl substitution types are reported. Combined spectroscopic data, electrochemical analysis, and theoretical calculations show that the insertion of a single electron-deficient B unit into the aromatic backbone strongly affects the LUMO energy level. The insertion of additional B units has only a minor effect on the electronic properties. Cast films of oligomers with two alternated B rings (B,T,B inner core) display crystalline order. Bottom-contact FETs based on films cast on bare SiO2 show hole-charge mobilities of 1,×,10,3,5,×,10,3,cm2 V,1s,1 and Ion/Ioff ratios of 105,106. Solution-cast films of cyclohexyl-substituted compounds are amorphous and do not show FET behavior. However, the lack of order observed in these films can be overcome by nanorubbing and unconventional wet lithography, which allow for fine control of structural order in thin deposits. [source]

AB-Block Copolymer with Moving B Blocks as a Model for Interpolymer Complexes

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 5 2010
Olga S. Pevnaya
Abstract The conformational behavior of a single AB block copolymer is studied by Monte Carlo simulation. The A-A and A-B interactions have the character of excluded volume interactions while the B units attract each other; the attractive B blocks can move along the chain. The collapse transition of the chain with increasing attraction between the B units is analyzed. Intrachain separation of the A and B units takes place in the course of the chain collapse with the formation of "globule with a tail" conformations. The globule is formed by the attractive moving B blocks while the tail consists of the swollen A segments. The model of AB block copolymer with moving B blocks can describe the behavior of interpolymer complexes between a long macromolecule and shorter polymer chains. [source]

Rust of flax and linseed caused by Melampsora lini

MOLECULAR PLANT PATHOLOGY, Issue 4 2007
GREGORY J. LAWRENCE
SUMMARY Melampsora lini, while of economic importance as the causal agent of rust disease of flax and linseed, has for several decades been the ,model' rust species with respect to genetic studies of avirulence/virulence. Studies by Harold Flor demonstrated that single pairs of allelic genes determine the avirulence/virulence phenotype on host lines with particular resistance genes and led him to propose his famous ,gene-for-gene' hypothesis. Flor's inheritance studies, together with those subsequently carried out by others, also revealed that, in some cases, an inhibitor gene pair and an avirulence/virulence gene pair interact to determine the infection outcome on host lines with particular resistance genes. Recently, avirulence/virulence genes at four loci, AvrL567, AvrM, AvrP4 and AvrP/AvrP123, have been cloned. All encode novel, small, secreted proteins that are recognized inside plant cells. Yeast two-hybrid studies have shown that the AvrL567 proteins interact directly with the resistance gene protein. The molecular basis of Flor's gene-for-gene relationship has now been elucidated for six interacting gene pairs: those involving resistance genes L5, L6, L7, M, P and P2, where both the resistance gene and the corresponding avirulence gene have been cloned. In other inheritance studies it has been shown that M. lini does not possess a (+) and (,) mating system, but may possess a two factor system. Double-stranded (ds) RNA molecules occur in many strains of M. lini: examination of the progeny of one strain that possesses 11 dsRNA molecules revealed that they fall into three transmission units, designated L, A and B. The L unit consists of a single large dsRNA of 5.2 kbp while the A and B units each consist of five dsRNAs in the size range 1.1,2.8 kbp. The three units have different sexual and asexual transmission characteristics. The L unit is encapsidated in a virus-like particle, whereas the other units are not encapsidated. The population and coevolutionary aspects of M. lini on a wild, native Australian host species, Linum marginale, have been extensively investigated. A recent molecular analysis revealed that the M. lini isolates from L. marginale fall into two distinct lineages, one of which is apparently hybrid between two diverse genomes. Isolates in this lineage are largely fixed for heterozygosity, which suggests that sexual recombination does not occur in this lineage. [source]

Synthesis and polymerization reactions of cyclic imino ethers.

POLYMER ENGINEERING & SCIENCE, Issue 8 2007

To study the effect of nonequal reactivity of B units in ABx monomers, two novel monomers for synthesis of hyperbranched polymers of the polyaddition type, namely 2-(2,5-dihydroxyphenyl)-2-oxazoline (2a) and 2-(2,4-dihydroxyphenyl)-2-oxazoline (2b) were prepared and characterized. Both monomers have one free phenolic group and one hydrogen-bonded phenolic group with the difference in chemical shift more than 2 ppm. Both monomers undergo thermally initiated polymerization in bulk and in solution at the temperature 220°C during 1 h in bulk and 24 h in solution of 1-chloronaphthalene. Products are white powders with degree of polymerization 17 and 13 for the respective polymer 3a and 3b. The degree of branching is 0.37 and 0.3 for the respective polymer. The structure of polymers is in agreement with the structure, which was expected from the structure of monomers and consists of linear, dendritic, and terminal units. POLYM. ENG. SCI., 47:1272,1280, 2007. © 2007 Society of Plastics Engineers [source]