Light-scattering and viscometric results are presented from micellar solutions of (PI)2PS (I2S) and (PS)2PI (S2I) three-miktoarm stars and a PSPI (SI) diblock copolymer in n-decane. The influence of architecture on the micellization properties of simple graft copolymers is investigated by keeping the overall molecular weights and compositions of the samples constant. All samples formed spherical micelles in n-decane, a selective solvent for polyisoprene. Aggregation numbers were found to increase in the order I2S < S2I < SI. Hydrodynamic radii of the micelles increased in the same order. The thickness of the corona is determined by the length of the soluble blocks, which they were found to be stretched to almost the same extent in all cases. The area of the core−corona interface per copolymer chain, A c, depends on the architecture of the molecule, and it is larger in the case of I2S micelles. In the case of S2I, larger A c values were found compared to the SI reference sample, indicating that the PS arms are arranged in different ways in the two kinds of micelles. The presence of only one grafted chain per molecule can change considerably the micellar characteristics of complex block copolymers. A simple scaling theory is developed taking into account the free energy contributions from the core, the corona, and the interfacial region of the micelle in the different cases. Theoretical predictions agree qualitatively with the experimental results.

The statics and dynamics of cw-functionalized diblock copolymers of styrene and isoprene have been studied with small-angle X-ray scattering (SAXS) and with rheology and dielectric spectroscopy. The asymmetric diblock copolymers (wps «= 30%) had a dimethylamino or zwitterion group at either end of the chain, and the molecular weights were in the range (0.62-2.44) x 104. Depending on the temperature, the SAXS results revealed two separate levels of microphase separation, one between the polystyrene (PS) and polyisoprene (PI) blocks forming the microdomain structure and another one between ionic and nonionic material. The latter process creates sufficient contrast notwithstanding the small fraction of the zwitterionic groups. When the zwitterion is linked to the PI chain end, aggregates are formed at low temperatures within the PI phase. These aggregates manifest themselves both in rheology and in dielectric spectroscopy, respectively, with an extended rubbery plateau and with a new dielectric process associated with restricted PI segmental relaxation. When the zwitterion is located on the PS chain end, association takes place, at high temperatures, within the PS phase and acts to stabilize the new microdomain up to very high temperatures. When compared with neutral diblocks, the co-functionalized diblock copolymers constitute a new class of materials which provide the possibility of altering the phase behavior by introducing a small amount of a polar group at one chain end.

A‐factor C13H22O4 was shown to be not only the inductor of the biosynthesis of streptomycin in inactive mutants of Streptomyces griseus (Actinomyces streptomycini), but also the potent regulator of differentiation of the cells: it induces the formation of spores in asporogenous strains during their superficial and submerged growth. This is accompanied by morphological modifications in the course of growth of the colonies.

No abstract

No abstract