Rheology dendrimers

ARCHITECTURAL FEATURES OF DENDRIMER MOLECULES THAT AFFECT THEIR RHEOLOGICAL BEHAVIOR... 

Thus, dendrimers exhibit a unique combination of (a) high molecular weights, typical for classical macromolecular substances, (b) molecular shapes, similar to idealized spherical particles and (c) nanoscopic sizes that are larger than those of low molecular weight compounds but smaller than those of typical macromolecules. As such, they provide unique rheological systems that are between typical chain-type polymers and suspensions of spherical particles. Notably, such systems have not been available for rheological study before, nor are there yet analytical theories of dense fluids of spherical particles that are successful in predicting useful numerical results. 

Compared to dilute solution viscometry and to some extent to bulk rheology, the flow properties of dendrimers in concentrated solutions have been the least investigated area of dendrimer rheology. In fact, with the notable exception of some recent data on generation 4 PPI in water [22] the only [32] reported... 

Hence, it seems that bulk dendrimers change their rheological behavior from Maxwell-like at lower generations to Rousean at higher ones. For PAMAMs for... 

It was also noted by Farrington and co-workers that the chemical nature of the end-groups may have a substantial effect on the viscosity of bulk dendrimers, even under iso-free volume conditions [49]. This seems consistent with the establishment of interdendrimer interactions and supramolecular organization at rest in the bulk state. However, as in most other areas of dendrimer rheology, more data are desirable before definite conclusions can be drawn. 

Although a body of data on dendrimer rheological behavior has been accumulated, and new reports are appearing at an increasing pace, the field is still in its infancy and will remain an intriguing and important subject of research for some... 

A paper on The rheological properties of poly(fluorophenylene germane) dendrimers was published by Myasnikova and co-workers in the Russian journal Polym. Sci., Ser. 

B., 37, 362 (1995). The authors claimed that acetone solutions (5, 10 and 20%, specifically) of a sample that had gel permeation chromatography retention time close to that of a linear polystyrene of 1.1 x 106 molecular mass, had four decades lower viscosity than the corresponding solutions of flexible-chain linear poly(butyl methacrylate). However, in our opinion, neither the examined sample was characterized satisfactorily enough to be referred to as a dendrimer, nor the rheology was described sufficiently enough to draw any conclusions about the solution s flow behavior. Therefore, we refer to this paper here only for reasons of curiosity. 

Like many polymers, the fluidity or flow (rheological) properties of denrimers are of interest (Box 14.1). Dendrimers behave like soft, spherical particles, surrounded by a hard surface shell and hence are often described as core-shell type bodies. Hence the interior of dendrimers can be deformed according to the type of linkage and building blocks and my contain voids suitable for encapsulating guest species.2... 

Uppuluri, S., Keinath, S. E., Tomalia, D. A., Dvornic, P. R., Rheology of dendrimers. I. Newtonian flow behavior of medium and highly concentrated solutions of polyamidoamine (PAMAM) dendrimers in ethylenediamine (EDA) solvent. Macromolecules 1998, 31, 4498-4510. 

Hyper-branched aliphatic polyesters are different from linear polyesters because of their unique mechanical and rheological properties, which can easily be tailored by changing the nature of the end group [156-159]. Both dendrimers and hyper-branched macromolecules are prepared from AB2 monomers, using dif-... 

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