Hyperbranched macromolecule synthesis

A wide range of other monomer units have been employed in the synthesis of hyperbranched macromolecules and the range of structures obtained is nearly as diverse as those for dendritic macromolecules. For example, hyperbranched polyphenylenes [93], polyesters [104, 107-109], polyethers [110-112], polyamides [113], polysilanes [114], polyetherketones [100], polycarbazoles [115], etc. [116-118] have been prepared. Interestingly, a number of groups have also used growth processes other than condensation chemistry to prepare hyper-... 

Synthesis of the phenolic bromide building block 40 was similar to the that of previously reported monomer 48 but the alkyl chain spacer unit was shortened in an attempt to increase the nematic mesophase isotropization temperature. 50 Construction of the related building blocks 41 and 42 followed similar pathways the latter were prepared to create hyperbranched macromolecules with a broader mesophase. 50 ... 

Scheme 1. Synthesis of hyperbranched macromolecules one terminal SiH group, n+l vinyl groups (n = II).

Starburst dendrimers have received considerable attention in the area of heterogeneous catalyst synthesis in the last decade. Although Tomalia et al. and Bosman et al. originally discovered these hyperbranched macromolecules and their host-guest properties in the mid-1980s. Crooks and coworkers were the first to demonstrate the ability of poly(amidoamine) (PAMAM) starburst dendrimers to act as metal nanoparticle stabilizers that could potentially aid in the synthesis of supported metal catalysts. The benchmark work of Crooks et al. and subsequent literature reports have underscored the advantages of successfully utilizing PAMAM dendrimer-nanocomposite precursors over conventional catalyst preparation methods. 

Hyperbranched Macromolecules. Because of their close structural and synthetic similarities to dendrimers, the comparison of hyperbranched macromolecules with their dendritic analogs has been studied by a number of groups. Ihre and Hult(7i) have recently reported the synthesis and characterization of the dendritic analogs of the commercially available hyperbranched polyesters, Boltron(D(7, based on 2,2-bis(hydroxymethyl)propionic acid, while Moor iJ) has reported a novel solid-supported synthesis of hyperbranched poly(phenylacetylenes) which are the hyperbranched analogs of Moore s well studied phaiylacetylene dendrimers(id). An intriguing study was also reported by Feast into the synthesis and physical properties of hyperbranched analogues of Tomalia s poly(amidoamine) dendrimers (77). 

This shows that AFM analysis of isolated hyperbranched macromolecules of relatively high molar mass is a powerful tool to investigate their size and architecture. It also allows investigation of the elementary chemical reactions occurring during the polymer synthesis and their selectivity, highlighting the main side reactions responsible for the formation of ill structures. 

Shi J, Jim CJW, Mahtab F, Liu J, Lam JWY, Sung HHY, Williams ID, Dong Y, Tang BZ (2010) Ferrocene-functionalized hyperbranched polyphenylenes synthesis, redox activity, light refraction, transition-metal complexation, and precursors to magnetic ceramics. Macromolecules 43 680-690... 

The fundamental requirements for the synthesis of dendrimers and hyperbranched macromolecules is examined. Examples of the divergent and convergent approaches are presented and a comparison of both methods with respect to each other and also the one-step procedure for hyperbranched macromolecules is made. The structural similarities and differences between dendrimers and hyperbranched macromolecules are described and the effect of this on the physical properties of these novel three-dimensional materials is discussed. Finally, a comparison of these materials with linear polymers is examined. 

Concerted efforts to examine the synthesis and polymerization of such ABx monomers was however not attempted until 1989 when Kim and Webster (17) reported their preparation of hyperbranched polyphenylenes fi-om the AB2 monomers, 3,5-dibromophenyl boronic acid, 7, or 3,5-dibromophenyl magnesium bromide, 8 (Figure 1). In a similar way to dendrimers, the field of hyperbranched macromolecules has been extended considerably since this initial report. Hyperbranched polyesters based on fully aromatic, fiilly aliphatic, or partially aliphatic/aromatic systems have been extensively studied by a number of groups (18-20). Similarly, hyperbranched poly(etherketones) (21), poly(ethers) (22), poly(urethanes) (23), poly(siloxanes) (24), etc. have been prepared using classical step growth chemistry. 

Tabuani, D., Monticelli, O., Chincarini, A., Bianchini, C., Vizza, F., Moneti, S. and Russo, S. (2003) Palladium nanopartides supported on hyperbranched aramids synthesis, characterization, and some applications in the hydrogenation of unsaturated substrates. Macromolecules, 36,4294. 

Dendrimers produced by divergent or convergent methods are nearly perfectly branched with great structural precision. However, the multistep synthesis of dendrimers can be expensive and time consuming. The treelike structure of dendrimers can be approached through a one-step synthetic methodology.31 The step-growth polymerization of ABx-type monomers, particularly AB2, results in a randomly branched macromolecule referred to as hyperbranch polymers. 

Paulo, C. and Puskas, J.E. Synthesis of hyperbranched polyisobutylenes by inimer-type living polymerization. I. Investigation of the effect of reaction conditions. Macromolecules, 34, 734, 2001. 

Keywords Macromolecules m Dendrimers m Fractal Structure m Hyperbranched Polymers m Nanostructure m Divergent Synthesis m Convergent Synthesis m Dendrylation... 

Parzuchowski PG, Grabowska M, Tryznowski M, Rokicki G (2006) Synthesis of glycerol based hyperbranched polyesters with primary hydroxyl groups. Macromolecules 39 7181-7186... 

Fang, J., Kita, H., and Okamoto, K. 2000. Hyperbranched polyimide for gas separation applications. 1. Synthesis and characterization. Macromolecules, 33,4639—4646. 

Hao, J. J., Jikei, M., and Kakimoto, M.A. 2003. Synthesis of hyperbranched aromatic polyimides having the same repeating unit by AB2 self-polymerization and A2 + B3 polymerization. Macromolecules, 36, 3519-3528. 

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