Hyper-branched polymers

Foreman, E.A., Puskas, J.E., and Kaszas, G., Synthesis and characterization of Arborescent (hyper-branched) polyisobutylenes from the 4-(l,2-oxirane-isopropyl) styrene inimer. J. Polym. Set Polym. Chem., 45, 5847, 2007. 

Hyper-Branched Polymers Based on Aryl-Metal Complexes. 44... 

Hyper-Branched Polymers Based on Alkynyl-Metal Complexes. 48... 

Reinhoudt and coworkers studied the synthesis of hyper-branched polymers composed of organopalladium complexes with an SCS pincer ligand [11]. Removal of acetonitrile ligands on palladium led to the self-assembly of dinu-clear palladium complex (9) to give hyper-branched polymer (10), which was... 

Scheme 6. Syntheses of hyper-branched platinum-acetylide polymers 20 and 21...

On the other hand, self-polycondensation of AB2 type monomer 22 produced soluble polymer 23 M =16,QQQ,MJM =1.29,) [25] (Scheme 7). Concentration of the monomer showed little influence on the molecular weight of the resulting polymers. and NMR spectra suggested that the polymer has a hyper-branched sphere partially involving a cyclic structure. 

A prerequisite for the application of filtration methods is a significant difference in molecular size of the catalyst and the reactants / products. Molecular enlargement, i.e. binding the homogeneous catalyst to soluble supports, is often the method of choice. These supports can be dendrimers, hyper-branched polymers or even simple polymers, giving the opportunity to tailor the support according to the given process. 

Fig.1. Schematic description of dendritic polymers comprising dendrimers and hyper-branched polymers...

Very recently, highly regular, highly controlled, dense branching has been developed. The resulting dendrimers often have a spherical shape with special interior and surface properties. The synthesis and properties of dendrimers has been reviewed (see e.g. G.R. Newkome et al. Dendritic Molecules , VCH, 1996). In this series, a chapter deals with the molecular dimensions of dendrimers and with dendrimer-polymer hybrids. One possible development of such materials may be in the fields of biochemistry and biomaterials. The less perfect hyper-branched polymers synthesized from A2B-type monomers offer a real hope for large scale commercialization. A review of the present status of research on hyperbranched polymers is included. 

Fig. 9.35 Schematic illustration of the self-condensing vinyl polymerization ATRSIP on planar silica substrates resulting in hyper-branched surface-bonded polymer layers.

Hyper-branched starburst poly(siloxysilane) polymers are synthesized through hydrosi-lylation-polymerization of CH2=CHSi(OSiMe2H)3 (269) and HSi(OSiMe2CH=CH2)3 (270). The polymer from 269 has Si—H moieties on the surface of the dendrimer, while that arising from 270 possesses vinyl groups on the outer sphere264. 

Novel, hyper-branched polyphenylenes 20 have been prepared by the selfcoupling of 3,5-dibromophenylboronic acid in the presence of Pd(PPh3)4 as shown in Scheme 25 [90,91]. (The monomer was prepared by treatment of the monolithiate of 1,3,5-triboromobenzene with trimethyl borate.) The hyper-branched polymer was found to be organic soluble, and could be converted to a water-soluble, polyphenylene derivative by treatment with butyl lithium followed by quenching with C02. The water-soluble nature of such hyper-branched polyphenylenes has made them suitable candidates for use in various applications such as unimolecular micelles. 

In contrast to perfect dendrimers with a degree of branching of 100%, hyper-branched polymers (Sections 2.7 and 4.1.5.4) will have degrees of branching between 50 and 85%, depending upon the monomer - for example, whether AB2 or ABg monomers were used as starting materials [37]. 

In our opinion an adequate distinction between ideal, defect-free dendritic molecules, for which we propose the term cascadanef, and the more or less defect-free (monodisperse) dendrimers , and polydisperse, imperfect hyper-branched compounds has so far been lacking in the area between polymer chemistry and small-molecule chemistry. Other reasons for such a distinction are because highly pure compounds have al-... 

Even in fields in which materials science had become somewhat routine and boring, such as the development of new polymers, unexpected and promising breakthroughs have occurred. The invention of polymers that conduct an electrical current—once considered a contradiction in terms—has made possible new substances with many of the advantages of traditional polymers and the added benefit of electrical conductivity. Like most other fields of materials research today, polymer research is turning out products with almost unheard of molecular structures, such as dendrimers and hyper-branched polymers. These products are so different from any natural or previously manufactured substance that researchers scarcely know the applications in which they may he employed. 

Hyper-branched polymers are prepared in a single-step polymerization from ABX monomers. Thus, a perfectly branched structure is present in dendrimers, whereas irregular branching is present in hyper-branched polymers. Aluminum alkoxide-based initiators or tin-based catalysts have been successfully used for the preparation of, hyper-branched [160-162, 166-168], dendrimer-like star polymers [160], and star-shaped polymers. The first and second generations of the benzyl ester of 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) are effective initiators for the ROP of lactones (e-CL) in the presence of Sn(Oct)2. The... 

A commercially available hyper-branched polyester derived from bis-MPA was used as the multifunctional initiating core for the ROP of e-CL and this led to the synthesis of hybrid dendritic linear star polymers. The reactivities of the chain-end hydroxymethyl groups in the dendrimer were significantly greater than in the isomeric hyper-branched case. 

As cheaper and readily accessible alternatives to regular dendrimers, hyper-branched polymers are increasingly being used as catalyst platforms. Rainer Haag has been one of the leaders in this field. He and C. Hajji provide an overview of an area for which commercial applications are most likely. Finally, all of these catalysis-related topics are complemented by a review of metallo-dendritic exoreceptors for the redox recognition of oxo-anions and halides, written by D. Astruc. This field offers new perspectives both for catalytic transformation and the development of molecular sensors. 

The variety of branched architectures that can be constructed by the macromonomer technique is even larger. Copolymerization involving different kinds of macromonomers may afford a branched copolymer with multiple kinds of branches. Macromonomer main chain itself can be a block or a random copolymer. Furthermore, a macromonomer with an already branched or dendritic structure may polymerize or copolymerize to a hyper-branched structure. A block copolymer with a polymerizable function just on the block junction may homopolymerize to a double comb or double-haired star polymer. 

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