Alginate was hydrophobically modified through a direct polycondensation of lactic acid grafting from sodium alginate. The results showed that nano particles with the diameters of 80~110nm were formed and uniformly distributed in the system. The nano particles were formed by hydrophobic interactions of polylactic acid segment. The modified alginate solution was dropped into calcium chloride solution to form microspheric beads. The release results showed that the newly prepared drug vehicle had enhanced drug loading rate and encapsulation efficiency

and it displayed slow release behavior. Drug release was fast in the weak alkaline solutions

but the release was nearly invisible in the acidic medium. The copolymer could be prepared as a pharmaceutical carrier for controlled release in the intestine.