Hyperbranched polymers chemical properties

Owing to multi-functionahty, physical properties such as solubihty and the glass transition temperature and chemical functionahty the hyperbranched (meth) acrylates can be controlled by the chemical modification of the functional groups. The modifications of the chain architecture and chemical structure by SCV(C)P of inimers and functional monomers, which may lead to a facile, one-pot synthesis of novel functionahzed hyperbranched polymers, is another attractive feature of the process. The procedure can be regarded as a convenient approach toward the preparation of the chemically sensitive interfaces. 

Changes in properties related to the architecture of hyperbranched polymers rather than the chemical structure have to some extent been evaluated but a full understanding is still lacking. Lately, research in this area has been focused on two questions why and to what extent the architecture affect the properties. 

Our work with perfect dendrimers continues. The goal is to synthesize at least four generations and then make extensive comparisons between hyperbranched polymers and dendrimers, both from a physical and chemical properties points of view. 

Dendrimers are a unique class of hyperbranched polymers with well-defined size, shape, and chemical functionality and with properties not found in classical linear and cross-linked polymers. There have been significant developments in the last decade in many areas of dendrimer research, partly due to the commercial availability of dendrimers such as PAMAM, but also the result of the synthesis of several novel dendritic structures. Numerous pharmaceutical applications have been proposed for these hyperbranched polymers, and given the rate of current developments, it is envisaged that dendrimer-based formulations will appear in the next decade. 

Alditols polyols are readily renewable, inexpensive and harmless to the environment. By incorporation of polyols into aliphatic polyesters, functional linear or hyperbranched polymers can be prepared with specific biological activities and/or that respond to environmental stimuli. Polyesters with carbohydrate or polyol repeat units in chains have been prepared by chemical methods. " In some cases, the reaction conditions led to hyperbranched polymers (HBPs). The highly branched architecture of HBPs leads to unusual mechanical, rheological and compatibility properties. " These distinguishing characteristics have garnered interest for their use in numerous industrial and biomedical fields. Chemical routes to linear polyol-polyesters require elaborate protection-deprotection steps ". Furthermore, condensation routes to hyperbranched polymers generally require harsh reaction conditions such as temperatures above 150 C and highly acidic catalysts ". ... 

J. Borah, S. S. Mahapatra, D. Saikia and N. Karak, Physical, thermal, dielectric and chemical properties of a hyperbranched polyether and its linear analog , Polym Degrad Stabil, 2006,91,2911-16. 

Precisely branched polymers include hyperbranched polymers, dendrimers and den-drons. Dendrimers and dendrons are characterized by perfectly controlled structures in three dimensions such as tree branch architecture, and they have attractive features such as a well-ordered chemical structure, molecular mass, size and configuration of polymers [5], Although the precise order of shape of hyperbranched polymers is less than that of dendrimers and dendrons, hyperbranched polymers have unique properties such as low viscosity attributed to the lack of entanglanent of polymer segments, and the possibility of chemical modification in terminal functional groups such as in dendrimers [1-3]. 

Type IV. Dendrimers and dendrons have perfectly and orderly branched tree-like structures. Their molecular mass increases with the growth of the number of generation. Dendrimers and dendrons, like common organic molecules, are perfectly controlled in terms of chemical structure, molecular mass, configuration and distribution of polymers [5]. Dendrons are well-ordered hyperbranched polymers and dendrimers are assembled from dendrons. It is expected that molecular-sized spaces between branched as well as hyperbranched polymers of dendrimers can be controlled and, therefore, could have high potential as gas separation membranes. An obvious disadvantage of dendrimers as membrane materials is their poor film-forming properties. 

Dendrimers are a class of macromolecules with a precisely controllable branched structure, consisting of three structural units a core, a hyperbranched scaffold and an external surface [16]. Dendrimers have been shown to possess unusual physical and chemical properties that differ significantly from those of linear oligomers and polymers. By using a fluorescent chromophore as the core of a dendrimer, one can apply fluorescence spectroscopy to study stmctural aspects and the conformational mobility of dendrimers in solution [17, 18]. At the same time, the dendritic shell provides a unique nanometer-sized environment for the spatial isolation of the chromophore, making them interesting materials for investigations by SMS. The synthesis of dendrimers with fluorescent chromophores attached to the rim serves as an efficient way to obtain a weU-defined number of chromophores in a confined volume [19-25]. Not only can the number of chromophores be easily controlled. 

Le, Tu. C., Todd, B. D., Daivis, P. J., and Uhlherr, A. Structural properties of hyperbranched polymers in the melt nnder shear via nonequihhrium molecular dynamics simulation. The Journal of Chemical Physics, 130,074901 (2009). 

The synthesis and properties of star polymers and dendrimers functionalized with ferrocene units has attracted a great deal of attention. The synthesis of high-generation dendrimers functionalized with chiral ferrocenyl units in their structures has been reported. The chiroptical properties of this class of dendrimer was dependent on the number of ferrocenyl groups and their chemical environment, but not on their position within the dendrimer. Deschenaux has reported the synthesis of hquid crystalline ferrocene-based polymers prossessing an enantiotropic smectic A phase. Ferrocene-functionahzed cyclic siloxane (29) and silsesquioxane branched polymers have also been reported. A hyperbranched polymer with a cubic silsesquioxane core was used to mediate the electrocatalytic oxidation of ascorbic acid. 

The ultimate success of dendritic macromolecules as a new class of specialty polymer will depend on these novel materials possessing either new and/or improved physical, mechanical, or chemical properties when compared to standard linear polymers. In this article, the difference between dendrimers and their linear or hyperbranched analogs will be examined and the effect of these different architectures on physical properties discussed. 

Dendrimers are a category of macromolecules that have a central core surrounded by hyperbranched repetitive units. Dendrimers have versatile structures and chemical properties because the core, the branches, and the external surface can have different functions. The hyperbranched structure of dendrimers distinguishes them from other macromolecules or polymers. For example, dendrimers have large number of end groups as well as higher concentrations of nanoporous channels and cavities because the number of dendrimer end groups increases faster than the surface area. 

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