Water-soluble polymers, dendrimers

Water soluble polymers such as poly(enolato-co-vinyl alcohol-co-vinyl acetate) (PEW) act as polymeric ligands to Rh in the biphasic hydroformylation of olefins.170 Another type of polymeric ligands are phosphinated dendrimers, i.e., regularly branched polymers with an almost spherical morphology, which carry PPh2 substituents on the surface, suitable, e.g., for attaching ruthenium complexes.171... 

Poly(ethylene oxide) (PEO) has been employed frequently as a water-soluble catalyst support [9]. Further water-soluble polymers investigated include other linear polymers such as poly(acrylic acid) [10], poly(N-alkylacrylamide)s [11], and copolymers of maleic anhydride and methylvinylether [12], as well as dendritic materials such as poly(ethyleneimin) [10a, c] or PEO derivatives of polyaryl ethers [13]. The term dendritic refers to a highly branched, tree-like structure and includes perfectly branched dendrimers as well as statistically branched, hyperbranched macromolecules. 

The thermal instability of rhodium-based hydroformylation catalysts has already been overcome commercially in the Ruhrchemie/Rhone-Poulenc process for propene hydroformylation in which the sodium salt of a sulfonated triphe-nylphosphine ligand (TPPTS, la) is used to solubilize the catalyst in the aqueous phase. In this process, the second phase is toluene and the reaction is carried out as a batch process with rapid stirring to intimately mix the two immiscible phases. After reaction, the system is allowed to separate and the organic phase is simply decanted from the aqueous catalyst phase. Both water-soluble polymers and PAMAM dendrimers have been reported as supports for rhodium-catalyzed hydroformylation under aqueous biphase conditions, but reactivities and regioselec-tivities were only comparable to or worse than those obtained with the reference TPPTS ligand. The aqueous biphase approach has found limited application for the hydroformylation of longer-chain alkenes, because of their very low solubility in water leading to prohibitively slow reaction rates, but there have been a variety of approaches directed at the solution of this problem. 

As regard to enzyme mimics formed with totally synthetic polymers, relatively simple water-soluble polymers with catalytic functionalities were employed in the early work before 1980.Although simulation of enzymatic behavior was successful to a certain extent by employing such prototype models, recent interests focused on more intelligent synthetic polymers, such as imprinted polymers and dendrimers. " ... 

Surface activity of these PAMAMOS dendrimers was determined by the Wilhelmy plate method for the water soluble dendrimers and by the Langmuir trough technique for the insoluble ones. Some preliminary data on water soluble PAMAMOS have already been published (5,42), It was shown that the best of these materials lower the surface tension of water to just below 30 mN/m at 5 wt. %, with no break to a constant surface tension that would indicate micelle formation. Thus, these PAMAMOS behave more like considerably surface active water soluble polymers than surfactants. However, it is probable that their homologues with longer siloxane dendrons than the trimethylsilyl- groups studied so far will have considerably more surfactant-like behavior. 

Gel electrophoresis is widely used in the routine analysis and separation of many well-known biopolymers such as proteins or nucleic acids. Little has been reported concerning the use of this methodology for the analysis of synthetic polymers, undoubtedly since in many cases these polymers are not soluble in aqueous solution - a medium normally used for electrophoresis. Even for those water-soluble synthetic polymers, the broad molecular weight dispersities usually associated with traditional polymers generally preclude the use of electrophoretic methods. Dendrimers, however, especially those constructed using semi-controlled or controlled structure synthesis (Chapters 8 and 9), possess narrow molecular weight distribution and those that are sufficiently water solubile, usually are ideal analytes for electrophoretic methods. More specifically, poly(amidoamine) (PAMAM) and related dendrimers have been proven amendable to gel electrophoresis, as will be discussed in this chapter. 

With the above-mentioned variety of addition reactions based on the addition-elimination mechanism almost any functional group or molecule can be attached to CgQ. Some examples are acetylenes [43, 52], peptides [53], DNA-fragments [53], polymers [54], macrocycles [55, 56], porphyrins [56, 57], dendrimers [58-60] or ligands for complex formation [56], Cjq can be turned into hybrids that are biologically active, water soluble, amphiphilic or mixable with polymers [53-55, 58, 61-69],... 

One of the possible alternative to micelles are spherical dendrimers of diameter generally ranging between 5 and 10 nm. These are highly structured three-dimensional globular macromolecules composed of branched polymers covalently bonded to a central core [214]. Therefore, dendrimers are topologically similar to micelles, with the difference that the strnctnre of micelles is dynamic whereas that of dendrimers is static. Thus, unlike micelles, dendrimers are stable nnder a variety of experimental conditions. In addition, dendrimers have a defined nnmber of fnnctional end gronps that can be functionalized to prodnce psendostationary phases with different properties. Other psendostationary phases employed to address the limitations associated with the micellar phases mentioned above and to modnlate selectivity include water-soluble linear polymers, polymeric surfactants, and gemini snrfactant polymers. 

Choi, J.S., Lee, E.J., Choi, Y.H., Jeong, Y.J. and Park, J.S. (1999) Poly(ethylene glycol)-block-poly(L-lysine) dendrimer novel linear polymer/dendrimer block copolymer forming a spherical water-soluble polyionic complex with DNA. Bioconjug. Chem., 10, 62-65. 

Typical polymeric pseudostationary phases include micelle polymers, polymeric surfactants, water-soluble anionic siloxanes and dendrimers [223-231]. Micelle polymers [e.g. poly(sodium 10-undecylenate), poly (sodium 10-undecenylsulfate), poly(sodium undeconylvalinate), etc.] are synthesized from polymerizable surfactant monomers at a concentration above their critical micelle concentration. These polymers have similar structures to micelles without the dynamic nature of the micelle structure. Polymeric surfactants are polymers with surfactant properties [e.g. acrylate copolymers, such as 2-acrylamide-2-methyl-l-propanesulfonic acid and alkyl methacrylamide, alkyl methacrylate or alkyl acrylate, poly (ally lamine)-supported phases, poly(ethyleneimine), etc]. Water-soluble anionic siloxane polymers are copolymers of alkylmethylsiloxane... 

The majority of active substances used currently are not very water-soluble. A very important technological task is to enhance water solubility. Three possibilities concerning polymers are going to be presented i) formulation of polymer dispersions and polymer solutions, ii) incorporation of apolar active substances into the micelles formed from copolymers, and iii) encapsulation of the active substance in dendrimers or its binding to the functional groups of the dendrimer [7, 9]. 

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