ensitive nanoparticles in order to increase the drug oral bioavailability where, the side chain of these polymers can be modified to possess pH-dependent solubility.
Poly (methyl methacrylate) nanoparticles were first investigated as adjuvants for injectable vaccines [126, 127] when the achievement of a very prolonged immune response is desired due to that they are very slowly biodegradable. They are also of a great value for basic body distribution studies where the determination of the fate of intact particles has to be followed over an extended time period.

Several copolymers of methyl methacrylate and ethyl acrylate were developed as ester components with methacrylic acid for use as enteric polymers. These polymers are manufactured by an emulsion-polymerization process and are obtainable in numerous forms. The polymer content of carboxyl groups is the major factor affecting the dissolution properties of the polymer. They are synthetic cationic and anionic polymers of dimethyl aminoethyl methacrylates, methacrylic acid and methacrylic acid esters in varying ratios.
Polymethacrylates are used as tablet binders, tablet diluents and film forming agents e.g. Cationic methacrylate, methacrylic acid copolymer Type A, Type B and Type C [128].
Eudragit®S 100 is an anionic copolymer based on methacrylic acid and methyl methacrylate which is soluble at pH of 7 or higher [128, 129] , the ratio of the free carboxyl groups to the ester groups is approximately 1:2 and mean relative molecular mass of about 135,000. Its pH-dependent polymer so, it’s usually used as an enteric polymer for controlling drug release in GIT. It is practically insoluble in water, petroleum ether, ethyl acetate and dichloromethane while, it is freely soluble in acetone, alcohols (including ethanol 95%, methanol and propane-2-ole) and 1N NaOH solution [128].
Eudragit S100 is insoluble in acidic medium and dissolves above neutral pH. Dissolution occurs as a result of structural change of the polymer associated with ionization of the carboxylic functional group.
At acidic pH, Eudragit S100 particles posses low permeability because of hydrogen bonding between the hydroxyl group of carboxylic moiety and the carbonyl oxygen of the ester group in the polymer molecules. This bonding increase degree of compactness of the polymer and decrease its porosity and permeability [130], minimizing release of an encapsulating agent.

When the pH of aqueous medium is increased, Eudragit S100 start to dissolve as carboxylic functional groups ionizes. The reported theoretical dissolution threshold is pH 7.0 and pKa of polymer molecules is believed to be approximately 6 [131]. Moreover, swelling of Eudragit S100 matrix may accompany the dissolution process contributing to release. It is believed that Eudragit S swells at pH above 6.5 [132].