Star polymers having hyperbranched structure

B. Self-Ordering of Star Polymer and Macromonomer Having Hyperbranched Structure... 

Anionic polymerization has proven to be a very powerful tool for the synthesis of well-defined macromolecules with complex architectures. Although, until now, only a relatively limited number of such structures with two or thee different components (star block, miktoarm star, graft, a,to-branched, cyclic, hyperbranched, etc. (co)polymers) have been synthesized, the potential of anionic polymerization is unlimited. Fantasy, nature, and other disciplines (i.e., polymer physics, materials science, molecular biology) will direct polymer chemists to novel structures, which will help polymer science to achieve its ultimate goal to design and synthesize polymeric materials with predetermined properties. 

Dendrimers branch perfectly with star-like topologies whereas hyperbranched polymers have imperfectly branched structures. Dendritic polymers have numerous sites per molecule to couple to active species, making them ideal carriers for drug molecules or biomacromolecules [96]. 

Ihe literature " describes a number of dendrimers and the closely related star-like 120-123 polysiloxanes. Ihe hyperbranched polysiloxanes are the primary example of more random structures. Although the emphasis has been on synthesis and characterization,i i modeling on hyperbranched polymers has also been carried out. Some of the most interesting species involve polysiloxane chains. Star polymers, some with nanosized silica cores, have also been synthesized.i °-i i Hyperbranched polysiloxanes have been prepared with controllable molecular weights and polydispersities,i -1 - with epoxy terminal groups some are UV-curable ° and some serve as a source of molecular silica. Hyperbranched polysiloxanes have also been used in the sol-gel preparation of polypropylene/silica nanocomposites. ... 

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 development of PPE synthetic chemistry makes the synthesis of PPEs with various structures possible. Recently, PPE-based polymers with different topological structures including linear random copolymers, block copolymers, star polymers, miktoarm polymers, and brush and hyperbranched polymers have been synthesized. Among them, linear homopolymers or random copolymers of PPEs are perhaps the most studied. Different block copolymers with AB, ABA, and ABC architectures have been synthesized by controlled ROP. By the combination of ROP of PPE with other controlled polymerization methods, such as living radical polymerization, or click chemistry, more complex architectures including miktoarm, comb, or graft copolymers can be synthesized. The richness of structures has allowed the convenient adjustment of material properties of PPE for biomedical applications. 

Comprehensive reviews of nomenclature for structure-based and source-based representations for dendritic, hyperbranched, and hypercrosslinked polymers, " " and for star and star-block polymers, have been completed recently. 

While A-B-A with composed alkylene dioxythiophene monomeric A units can be polymerized oxidatively to the corresponding polymer, linear (AB) and star branched polymers have to be made by organometallic reactions due to a low reactivity of the B unit. (AB) polymers with EDOT as the A unit and phenylene (Vlf) as well as fluorene (Vlg) structures as the B unit were synthesized by Suzuki polycondensation and show electrochromic behavior without any conspicuous properties. On the other hand, hyperbranched polymers with an additional triarylaminic core unit and similar composed branches made from 3,4-ethylenedioxythiophene and didodecyloxybenzene structures exhibited multicolor electrochromism to produce the three basic colors in the RGB system red, green, and blue. 

Star and hyperbranched (dendritic) polymers have attracted increasing attention in organic, supermolecular, and polymer chemistry as well as coordination chemistry because of their specific structures and characteristics [1-5]. For the preparation of these highly branched polymers, two kinds of synthetic methods have been developed a one-step pol)nnerization and a stepwise method. By the one-step method, various star and hyperbranched polymers with many structural and functional group variations have been prepared [6-10]. On the other hand, the stepwise method is quite useful, especially for the synthesis of dendritic polymers. Both divergent and convergent s)mthetic approaches have been employed [2,11]. 

Many micellar catalytic applications using low molecular weight amphiphiles have already been discussed in reviews and books and will not be the subject of this chapter [1]. We will rather focus on the use of different polymeric amphiphiles, that form micelles or micellar analogous structures and will summarize recent advances and new trends of using such systems for the catalytic synthesis of low molecular weight compounds and polymers, particularly in aqueous solution. The polymeric amphiphiles discussed herein are block copolymers, star-like polymers with a hyperbranched core, and polysoaps (Fig. 6.3). 

One of the ultimate branched polymers, as illustrated in Figure 5.11, has emerged since 1995 as a novel class of weU-defined hyperbranched polymers. Despite a variety of names having been proposed for these polymers, they have been termed recently as dendrimer-like star-branched polymers (DSPs), on the basis of their branched architectures, which are similar to those of well-established dendrimers. From a structural point of view, the DSPs represent promising specialty functional materials with many potential applications. 

It has been known that the molecular parameters, such as monomer nature, overaU molar mass, polydispersity, branching degree and distribution of subchain lengths, strongly affect the final macroscopic properties of polymers. Therefore, great research interest has been paid to the synthesis of various weU-defined polymers with different topologies, such as cycUc [7-13], star branched [14-16], mikto-star [17-19], and H-shaped [20, 21] polymers, and the study on their structure-property relationship. In contrast, to establish the structure-property relationship of hyperbranched polymers, a series of narrowly distributed samples (standards) with a well-defined structure have to be prepared before any possible study. 

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