Hyperbranched Condensation Polymers

Anion-exchange stationary phases described in Section 3.4.1.4 are based on colloidal anion-exchange particles (the so-called nanobeads or latex particles) that are electrostatically bound to the surface of nonporous surface-sulfonated or sur-face-carboxylated PS/DVB and EVB/DVB copolymer beads. This approach to stationary-phase design provides a number of advantages including the following  

However, there are also a number of shortcomings of the polymeric media to produce such colloidal particles. These are as follows  

The underlying factors behind the selectivity differences between anion-exchange materials based on styrenic and methacrylate monomers are not fully understood. It is likely that these differences can be attributed to the n electrons in the styrenic polymer. Thus, Pohl and Saini [38] were searching for a methodology to synthesize an anion-exchange material free of any k electron character in the polymer backbone. A particularly interesting system for synthesizing a cationic condensation polymer involves the reaction of diepoxides with primary amines. When diepoxides and primary amines are allowed to react in a 1 1 molar ratio, the product is a water-soluble polymer with a predominantly linear architecture. 

Initial experiments by Pohl and Saini [38] were carried out with 1,4-butane-diol diglycidyl ether (BDDGE), because it is available in reasonably high purity ( 95%) unlike most other diepoxide monomers. 

Carbonate-Selective Hyperbranched Condensation Polymers The synthesis method described above was used for the development of four carbonate-selective hyperbranched condensation polymers, lonPac AS22, lonPac AS22-Fast, lonPac AS22-Fast-4pm, and lonPac AS23. The technical characteristics of these columns are summarized in Table 3.8. 

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The step-growth polymerization of ABx-monomers is by far the most intensively studied synthetic pathway to hyperbranched polymers. A number of AB2-monomers, suitable for step-growth polymerizations, are commercially available. This has, of course, initiated substantial activity in hyperbranched condensation polymers and a wide variety of examples have been reported in the literature [4],... 

Similar methods can be used to construct universal plots for molar mass distributions of linear and hyperbranched condensation polymers. The number distribution function n p, N) for linear condensation polymers is obtained from the number fraction distribution [Eq. (1.66)] ... 

Figure 3.58 Separation of inorganic and organic anions as a function of the reaction cycle number with a BDDGE-methyl amine-based hyperbranched condensation polymer. Column dimensions 250 mm x 4 mm i.d. column temperature 30 °C eluent 5 mmol/L KOH (EG) flow rate 1 mlVmin detection ...

Table 3.8 Structural and technical properties of carbonate/bicarbonate-selective, hyperbranched condensation polymers.

The unique selectivity of modern hyperbranched condensation polymers such as lonPac AS22 allows the simultaneous analysis of mineral acids and a wide variety of polarizable anions with a carbonate-based eluent under isocratic conditions in less than 30 min (Figure 3.131). Even strongly retained analytes such as perchlorate, thiosulfate, and chromate elute as symmetric peaks from this column. In contrast to the respective separation on an acrylate-based anion exchanger in Figure 3.130, fluoride is well separated from the system void. 

Figure 3.131 Separation of mineral acids and polarizable anions on a hyperbranched condensation polymer. Separator column lonPac AS22 column temperature 30 °C eluent ...

A shortcoming with condensation polymers, is their sensitivity towards hydrolysis, which might restrict the use of such polymers in certain applications. For that reason, some hyperbranched polymers are synthesized via substitution or ring opening reactions that provide more hydrolytically stable polymers. 

Figure 8.5 Schematic representation of the self-condensing vinyl polymerization of an AB -monomerto give a hyperbranched vinyl polymer [19]...

A wide variety of hyperbranched polymers have been described in the literature. Initially, these were mainly condensation polymers such as polyesters and polyethers since the required monomers were the most readily available. A number of hyperbranched polymers based on vinyl monomers have been described lately after the introduction of self-condensing vinyl polymerization. One structural variation which has been widely employed for hyperbranched... 

Condensation polymerizations (polycondensations) are stepwise reactions between bifunctional or polyfunctional components, with elimination of small molecules such as water, alcohol, or hydrogen and the formation of macromo-lecular substances. For the preparation of linear condensation polymers from bifunctional compounds (the same considerations apply to polyfunctional compounds which then lead to branched, hyperbranched, or crosslinked condensation polymers) there are basically two possibilities. One either starts from a monomer which has two unlike groups suitable for polycondensation (AB type), or one starts from two different monomers, each possessing a pair of identical reactive groups that can react with each other (AABB type). An example of the AB type is the polycondensation of hydroxycarboxylic acids ... 

Gelation processes, such as crosslinking linear chains or condensation of /-functional monomers A/ (where A reacts with A) with /> 2 are quite different from either linear condensation polymers or hyperbranched polymers. Linear condensation polymers (made from AB monomers, -where A only reacts with B) and hyperbranched polymers (made from... 

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