R Kleppinger

The Localization of Guests in Water-Soluble Oligoethyleneoxy-Modified Poly(propylene imine) Dendrimers

Small-angle X-ray scattering measurements and UV/Vis titrations have been used to characterize a new water-soluble host?–?guest system based on oligoethyleneoxy-modified poly(propyleneimine) dendrimers. These experiments indicate that unique interactions between the host and guests lead to a specific location of the guests in the core of the dendrimers (see schematic representation).

Ordering phenomena in ABA triblock copolymer gels

Temperature and concentration dependencies of the degree of order in ABA triblock copolymer gels are discussed. Two factors can influence the ordering phenomena: the conformation of the midblocks (links of the network) and the polydispersity of the endblock domains (nodes of the network). The latter is defined by the scattering density profile (polymer chain packing) at the domain boundary: a sharp boundary corresponds to less polydisperse domains and to increased order in the arrangement of the network nodes. The structure of the network can be described in terms of a highly distorted crystalline lattice with close-packed spheres or with cubic (presumably BCC) equilibrium morphology. The appearance of the latter is never detected in the gels with a stretched conformation of the midblock.

Networks of gel-forming triblock copolymer solutions: In situ SANS and rheological measurements

Abstract Triblock copolymers in a solvent, selective for their middle blocks provide the basis for the formation of novel physical networks where cross-links are formed by self-assembled domains of the end-blocks. Triblock copolymers of poly(styrene)-poly(ethylene,butylene)-poly(styrene) (SEBS) dissolved in a mixture of aliphatic and alicyclic compounds constitute such a network system. Using a Rheometrics RSA-2 instrument modified for in situ measurements of small-angle neutron scattering and rheology provides a unique possibility for detailed understanding thermodynamics of such a gel. The self-association of the PS-blocks do not only promote formation of highly inter-connected end-block domains, but within a narrow temperature range these domains furthermore constitute a network with body-centered cubic (BCC) microstructure. Upon large amplitude oscillating shear the polycrystalline soft gel can be aligned into a twinned BCC monodomain.