Molecular weight distribution hyperbranched polymers

As early as 1952, Flory [5, 6] pointed out that the polycondensation of AB -type monomers will result in soluble highly branched polymers and he calculated the molecular weight distribution (MWD) and its averages using a statistical derivation. Ill-defined branched polycondensates were reported even earlier [7,8]. In 1972, Baker et al. reported the polycondensation of polyhydrox-ymonocarboxylic acids, (OH)nR-COOH, where n is an integer from two to six [ 9]. In 1982, Kricheldorf et al. [ 10] pubhshed the cocondensation of AB and AB2 monomers to form branched polyesters. However, only after Kim and Webster published the synthesis of pure hyperbranched polyarylenes from an AB2 monomer in 1988 [11-13], this class of polymers became a topic of intensive research by many groups. A multitude of hyperbranched polymers synthesized via polycondensation of AB2 monomers have been reported, and many reviews have been published [1,2,14-16]. 

Random hyperbranched polymers are generally produced by the one-pot polymerization of ABX monomers or macromonomers involving polycondensation, ring opening or polyaddition reactions hence the products usually consist of broad statistical molecular weight distributions. 

For a theoretical description of crosslinking and network structure, network formation theories can be applied. The results of simulation of the functionality and molecular weight distribution obtained by TBP, or by off-space or in-space simulations are taken as input information. Formulation of the basic pgf characteristic of TBP for crosslinking of a distribution of a hyperbranched polymer is shown as an illustration. The simplest case of a BAf monomer corresponding to equation (4) is considered ... 

In agreement with Flory s predictions, hyperbranched polymers based on A,jB monomers reported in the literature exhibit a broad molecular weight distribution (typically 2-5 or more). The polydispersity of a hyperbranched polymer is due to the statistical growth process. A strategy to overcome this disadvantage is to add a By-functional core molecule, or a chain terminator, which Hmits the polydispersity and also provides a tool to control the molecular weight of the final polymer. The concept of copolymerizing an A2B monomer with a B3 functional core molecule was first introduced by Hult et al. [62] and more recently also utilized by Feast and Stainton [63] and Moore and Bharathi [64]. 

The potential loading capacity of these hyperbranched polymers is similarly high as for dendrimers (5-14 mmol g ) and some hyperbranched polymers are even commercially available [13,121]. The use of these commercial materials as supports for organic synthesis, however, is hmited due to the chemical stability of the respective polymer backbone (e.g. polyamines, polyesters) and the relatively broad molecular weight distributions (typically PD>2) [13]. Therefore, new hyperbranched species have been developed. 

Yan, D. Zhou, Z. Muller, A. Molecular weight distribution of hyperbranched polymers generated by self-condensing vinyl polymerization in the presence of a multifunctional initiator. Macromolecules 1999, 32, 245. 

Hyperbranched polymers are more simple to produce on a large scale than dendrimers. Generally, a one-pot synthesis is used, yielding fewer regular structures and very broad molecular weight distributions (45). 

Radke, W, Litvinenko, G, and Mtlller A. H. E. Effect of core-forming molecules on molecular weight distribution and degree of branching in the synthesis of hyperbranched polymers. Macromolecules, 31,239-248 (1998). 

Muller, A.H.E., Yan, D., and Wulkow, M. (1997) Molecular parameters of hyperbranched polymers made by self-condensing vinyl polymerization. 1. Molecular weight distribution. Macromolecules, 30,7015-7023. 

Surprisingly narrow molecular weight distributions (M /Mn= 1.26-1.43) at molecular weights up to 5000 gmol" were found. Detailed characterization of the hyperbranched polymers by proton-decoupled NMR experiments showed a correlation between monomer conversion and the DB. While at low conversions (<30%), predominantly linear units were formed, increased conversion... 

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