Dendrimers flow properties

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... 

As compatibilizers, dendritic poly(ester) resins are useful. This covers both dendrimers and hyperbranched polymers (51). Compatibilizers are needed, because conventional poly(arylene ether)/PA blends exhibit inadequate flow properties at the processing temperatures that are needed to minimize the thermal degradation of the resins. However, increasing the processing temperature beyond these temperatures in order to reduce viscosity of the blends results in brittle parts and surface imperfections in the final part. 

In past several strategies were used to improve flow properties of polymers. Key strategies explored were a) Long chain branching of polymers via reactor technology[l], b) Use of additives such as dendrimers or Hyperbranched polymers as flow promoters [2] and c)... 

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... 

Thermal properties of carbosilane dendrimers have also been described. A recent report examined Tg and other temperature-related behavior in a series of dendrimers up to the seventh generation (Figure 3)37. For the third generation, a Tg of — 95 °C was observed, while a Tg of approximately — 86 °C was observed for the fourth through seventh generations. These researchers also investigated flow temperatures and viscoelastic behavior of the dendrimers. 

Theoretical description of dendritic structures is an active but difficult topic because the length between branched points is close to or even smaller than the Kuhn length, above which the segments can be thought of as if they are freely jointed with each other. Most modeling or simulation work has focused on the quasi-static and rheological properties of hyperbranched polymers and dendrimers in shear flow [240, 244, 255-263]. Limited amounts of data were published for dendrimers and hyperbranched polymers within elongational flow field. 

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