PH-dependent swelling

JH Kou, GL Amidon, PI Lee. pH dependent swelling and solute diffusion characteristics of poly(hydroxyethyl methacrylate-co-methacrylic acid) hydrogels. Pharm Res 5 592-597, 1988. 

The pH responsiveness of a 3-PAA/Au graft that was amidated with N,N-dimethylaminoethylenediamine was also studied by in situ ellipsometry [32]. This amine-containing graft had pH dependent swelling characteristics that were opposite to those of the - C02H-rich graft because the amine-rich film... 

Drug delivery induced by swelling may be achieved with swellable polymer layers based on cellulose ethers or acrylates, where with the latter pH-dependent swelling behaviour is feasible [92]. Examples are the oral Chronotopic delivery system [93], the Tune-controlled Explosion ystem (TES) [94,95] and the TIME-CLOCK -System [96-98] (Figure 6.4). 

The negative value of the second virial coefficient and the low value of the reduced viscosity at pH = 2.1 confirm a globular conformation of the polymer particles at the lEP [212]. The pH-dependent swelling behavior of the PCIEAC gel is consistent with its linear analogue and a minimum at pHiEp 2.1-2.2. 

Loxley, A. Vincent, B. Equilibrium and kinetic aspects of the pH-dependent swelling of poly (2-vinylpyridine-co-styrene) microgels. Colloid Polym. Sci. 1997, 275 (12), 1108-1114. 

A polyelectrolyte gel (pH-dependent swelling) is immersed in a large solvent reservoir (pure solvent, no added ions). The system consists of three components polymer ions, counter ions, solvent molecules. Each of them contributes to the chemical potential. 

Kuckling D, Richter A, Amdt K-F (2003a) Temperature and pH dependent swelling behavior of poly(A-isopropyl-acrylamide)-copolymer hydrogels and their use in flow control. Macromol Mater Eng 288 144-151... 

Poly(methacrylic acid) and its derivatives are other polymers with pH-dependent swelling. Poly(methacrylic acid) is barely hydrophilic, whereas its sodium salts are easily dissolved in water. This property is used to prepare gastro-resistant coatings for tablets. Cross-linked poly(methacrylic acid) does not swell at low pH, but its salts swell above pH 6. Such polymers and copolymers have been used as matrices for intestinal controlled delivery of drugs. Conversely, linear polymers bearing amino groups are water-soluble at low pH, whereas cross-linked polymers are swollen. Castro-soluble and... 

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