Block polyampholyte

It increase with the charge fraction f and decreases with ionic strength. This is consistent with experiments on block polyampholytes where the pH is varied [198]. 

It was not until the 1970s that the first block polyampholytes were reported (251,252). Anionic polymerization was used to prepare precursor AB diblock copolymers of 2-vinylpyridine lOZ with trimethylsilyl methacrylate (TMSMA). The TMSMA residues were subsequently hydrolyzed to poly(methacrylic acid) residues to yield the corresponding AB diblock polyampholytes. Anionic poljnner-ization has also been employed to prepare other block polyampholytes (253-258). GTP has also been successfully employed for the preparation of block polyampholytes. As with anionic polymerization, protected acid monomers must be employed since methacrylic acid (MAA) cannot be polymerized directly by this technique. A variety of protected monomers have been reported to be suitable as a means of introducing MAA residues, with 2-tetrahydropyranyl methacrylate being the most effective (Fig. 46). 

While these living polymerization techniques do offer the ability to prepare block polyampholytes they are both synthetically demanding and somewhat limiting with respect to monomer choice for example. There are a handful of reports detailing the synthesis of block polyampholytes using controlled/living polymerization techniques discussed earlier (Fig. 47). For example, Gabaston and co-workers have described the TEMPO-mediated SFRP of block copolymers of sodium 4-styrenesulfonate IIZ with 4-(dimethylamino)methyl styrene 12Z (133),... 

Solution Properties. The aqueous solution behavior of polyampholytes is dictated by coulombic interactions between the basic and acidic residues. Polyampholytes have the ability to exhibit both polyelectrolyte and antipolylelectrolyte behavior in aqueous media. Which type of behavior is exhibited depends on factors such as solution pH, copolymer composition, the relative strengths of the acidic and basic residues, and the presence/absence of low molecular weight electrolyte (239). A feature of polyampholytes—in particular those comprised of weak acidic and basic residues—is the so-called isoelectric point, or lEP. This is simply defined as the solution pH at which the polyampholyte is electrically neutral. Statistical polyampholytes often remain soluble at and around the lEP whereas block polyampholytes tend to be soluble above and below but insoluble at this critical pH. The lEP may be determined either by titration or by measuring the reduced viscosity as a function of pH—the lEP also represents the point at which the polyampholyte chain is in its most compact conformation and thus corresponds to the minimum in reduced viscosity (239,266). With a knowledge of the respective piiLa s and copolymer composition it is also possible to predict the lEP (267). 

One interesting option is the interaction of polyampholytes with proteins this system has been studied by several authors [64, 65]. Polyampholytes are exclusively firom the industrial synthesis, they are derivatives of the polymethaacrylates such as (a) block polyampholytes with block sequences (dimethyl amino) ethyl methacrylate (cationic residue), methyl methacrylate (neutral, hydrophobic residue), and methacrylic acid (anionic residue) and (b) random polyampholytes of (dimethylamino) ethyl methacrylate, methyl methacrylate, and acrylic acid have... 

While the bulk behavior of polyampholytes has been investigated for some time now, studies of interfacial performance of polyampholytes are still in their infancy. There are several reasons for the limited amount of experimental work the major one being the rather complex behavior of polyampholytes at interfaces. This complexity stems from a large array of system parameters governing the interaction between the polymer and the substrate. Nearly all interfacial studies on polyampholytes reported to-date involved their adsorption on solid interfaces. For example, Jerome and Stamm and coworkers studied the adsorption of poly(methacryhc acid)-block-poly(dimethyl aminoethyl methacrylate) (PMAA-fc-PDMAEMA) from aqueous solution on sihcon substrates [102,103]. The researchers found that the amount of PMAA-fo-PDMAEMA adsorbed at the solution/substrate interface depended on the solution pH. Specifically, the adsorption increased... 

Protein-Pak Q-8HR (strong anion exchange, 8 fi particles) Block methacrylic polyampholytes /3-lactoglobulins A and B 27... 

The adsorption behavior of weak polyampholytes from aqueous solutions on to a solid wall is strongly determined by the pH of the polymer solution. So it is absolutely necessary to investigate the adsorption as function of pH. As an example the adsorbed amount of two polyampholytes with medium molecular weight of around 60,000 g mol-1 and different block sizes is shown in Fig. 14 [13]. In every case the isoelectric point IEP of the polymer, which is determined by the block ratio, is the prominent feature of adsorp-... 

Other investigations have been performed where silicon substrates were modified from alkaline to acidic and hydrophobic nature [58], where salt concentration was varied during adsorption [55] and where the nature of one of the blocks was changed [59]. Monolayers of polyampholyte micelles were used to modify protein adsorption [60]. An example is shown in Fig. 18 where the adsorption of fibrinogen is controlled by preadsorption of polyampholyte micelles and the phosphate buffer concentration. 

Fig. 17 Comparison between the maximum adsorbed amount of polyampholyte with two high molecular weights and one low molecular weight as function of the block ratio Mn 65,000 g mol-1, squares Mn=101,000 g mol-1, triangles Mn 14,500 g mol-1, circles...

Polymers containing three types of monomers are called terpolymers (Fig. 1.8). Examples of random terpolymers are polyampholytes containing positive, negative and neutral monomers. An example of block terpolymers are ABC triblocks shown in Fig. 1.8. 

Triblock and random polyampholytes based on DMAEM-MMA-MAA were examined for their phase separation behaviour [52]. Triblock polyampholytes have a much broader phase separation region than the random ones. The specific structure of PMAA-fc-PlM4VPCl with the excess of cationic or anionic blocks at the lEP is close to the structure of non-stoichiometric IPC. It is suggested that its nucleus consists of intraionic IPC surrounded by cationic blocks protecting it from precipitation [53]. ABC triblock copolymers of polystyrene-b/ock-poly(2-(or 4)vinylpyridine)-fc/ock-poly(methacrylic acid) were synthesized by living anionic polymerization [53 a]. Interpolymer complexation of the polyvinylpyri-dine and poly(methacrylic acid) blocks in the micellar solution was studied in relation to pH in solution by potentiometric, conductimetric and turbidimetric titration and in bulk by FTIR spectroscopy. 

Fig. 27. Variation of the electrokinetic potential of PSL particles on the concentration ol polyampholytes AA/DMVEP (curve i), MAA/TMVEP (curve 2), VMAA-block-VMVP (curve 3), AA/VI (curve 4). The dotted lines correspond to lack of stability of PSL...

Block Synthesis. Water-soluble block copolymers are formed from the copolymerization of macromonomers of methacrylates with acrylic and methacrylic acid monomers and their solution properties compared with random copolymers of similar composition (224). Diblock and triblock copolymers may be prepared by a number of techniques and are also used on ink-jet inks (225) and scale inhibition in water boilers (226), respectively. Associative properties of block polymers to form micellar structures are well established (227,228). Triblock polyampholyte polymers are also known (229). 

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