Polymer structure and dynamics, and polymer-polymer interactions

Abstract

Special architectures can be constructed from macromolecular building blocks by placing functional groups at well defined positions on the polymeric object. These functional groups can be linked together either by chemical reaction or by non-covalent bonds. Often, however, the position of the functional groups is not sufficiently well known, and no precise prediction can be made on the supramolecular structure that is formed. The problem is of particular complexity with associative structures which are formed at moderately high concentrations above the overlap concentration c ∗. Here the interparticle interactions have a big influence on the scattered light intensity, and only an apparent molar mass is measured at finite concentration. To eliminate this influence of interparticle interactions a number of well defined structures were synthesized, and the interaction was studied. These investigations revealed that the reduced osmotic modulus ( =M w M app(c) ) of self-similar objects can efficiently be described by a parameter X = A 2M wc ∼ c c ∗ , but the curves differ characteristically for the various architectures. Hence, an estimate of structures can be made from the forward scattering. With this knowledge on covalent structures a relationship could be derived that to a good approximation allowed the required elimination of the repulsive interaction on the scattered light. The technique is successfully applied to random associates from a globular protein and the fairly stiff cellulose 2.5-acetate chains, respectively. The special example of lateral chain aggregation is discussed in detail. Various experiments give strong evidence for the formation of a fringed micelle. This is a structure that consists of a stem of several laterally aggregated chain segments and freely dangling outer chains sections. These fringed micelles can associate reversibly when the concentration is increased, and display uncommon dynamic behaviour in the semidilute concentration regime. This is recognized by the asymptotes of Γ ∗ = ( Γ q 3 )( η 0 kT ) at values of qR g > 4. Γ ∗ is strongly reduced as the concentration is increased. The results demonstrate that little chain interpenetration has taken place and instead of this the outer chain sections of the fringed micelles were compressed losing thereby gradually the mobility of the dangling outer chain sections.