Betaines, polyampholytes

In the case of polyampholytes with a betaine structure (6), the acidic and basic groups are situated along the chain backbone. Dependent on the solubility of polyampholytes near the isoelectric point (lEP), they can be water soluble and water insoluble. For instance, the equimolar copolymers of aminoalkyl(meth) acrylates and unsaturated carboxylic acids are water soluble over the complete range of pH-values. On the contrary, copolymers based on vinylpyridines and acrylic (methacrylic, vinyl- or styrenesulfonic) acid are insoluble at the lEP. As a rule most blockpolyampholytes have a wide region of insolubility. Hydrophobic polyampholytes, the behaviour of which is close to polysoaps , represent the combination of zwitterionic and hydrophobic structures. 

Polymeric betaines or zwitterions are polyampholytes whose oppositely charged groups remote one from another are displaced on one pendant substituent. There are several types of monomers with a betaine structure carboxy-betaines, sulfobetaines and phosphobetaines. Poly-hT-ethyleneglycine (1), po-ly(N-3-sulfopropyl)-W-methacryloyloxyethyl-Nd -dimethylammonium betaine) (2) and poly[(2-methacryloyloxyethyl-2-(trimethylammonioethyl-phosphate)] (3) are typical examples of this kind of polyampholyte ... 

It is well understood that the choice of the underlying monomers used to synthesize polyelectrolytes, polyampholytes, and betaine polymers have a significant impact on the final properties of the resulting material. This is especially important when identifying polymers for use in biomedical applications, as the underlying chenfistry may not be tolerated well in the in vivo environment even if it has the most desirable physical characteristics. Because of this, only a subset of charged monomers has been adapted for biomedical applications. 

To create surfaces that are responsive to environmental cues, polyampholytes, polyelectrolytes, or betaine polymer coatings and/or materials must first be formed through controlled polymerization techniques. There are a number of excellent reviews on polymerization techniques (Barbey et al., 2009 Lowe McCormick, 2002 Matyjaszewski Xia, 2001), so only a brief overview of the most relevant approaches is provided here. 

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