Preparation Of Pharmaceutical Enteric-soluble Coating Material

The copolymer latex of Methacrylic acid(MAA), which can be used as enteric-soluble coating materials, was prepared in both batch and semi-batch seeded emulsion copolymerizations. The effects of emulsifier type and amount, initiator amount, copolymerization temperature, content of MAA, monomers feeding rate on the latex stability and monomers conversion were investigated. It was shown that a percentage of 2 wt.% MAA in monomers led to the acceleration of polymerization rate, while emulsion stability was not affected obviously. When the percentage of MAA was increased, more than 30 wt.%,the coagulation between latex particles and coagulum became serious with increasing MAA contents especially in the batch polymerization processes. However, the solubility of copolymers in alkali medium increased with increasing MAA contents in copolymer.It was shown that a reduction of the monomers feeding rate is favorable to the process. The growth of particles was studied primarily in the semi-batch seeded emulsion copolymerization, it was shown that the decrease of the monomers feeding rate and MAA content can promote copolymerization, obtaining smaller particles. Factors that influenced the enteric-solubility of the film were also studied. An increase of MAA content and decrease of the molecular weight of copolymer will favor the solution process.TEM result showed that the latex diameter was about 80nm, with a core-shell structure. The copolymer was also determined by 1H-NMR, IR, DSC spectra. The distribution of MAA in latex inside, latex surface, aqueous phase were characterized by conductometric and acidimetric titration.It was shown that the MAA concentration in aqueous phase increased with the increase of monomers feeding rate and MAA content,thus MAA in copolymer reduced due to the increasing tendency of MAA homopolymerization in water.