Study On Preparation Of Polylactic Acid And Polylactic Acid Microspheres

In recent years imidacloprid and acetamiprid are insecticides which develop rapidly at home and abroad. Their dosage forms are used primarily as EC and WP. However, traditional dosage forms need a lot of harmful solvents such as toluene and xylene which contaminate environment severely. Pesticide controlled release system could not only extend the time for drug concentration to enhance effects, but also reduce dosage and side effects. Recently polyurea, polyamide, polyurethane and other non-degradable materials which take up most of carrier materials cause new environmental problems.So the carrier materials of biodegradation are used more and more in drug controlled release system now. Polylactic acid(PDLLA), which gradually biodegrades into water and carbon dioxide, has good biocompatibility and biodegradability. Therefore, the research of drug carrier materials is now focused on families of polylactic acid. However, one of the biggest problems of PDLLA lays in its extremely high price and its application is limited, because the polymer is conventionally obtained by ring-opening polymerization process from lactide. In this paper, polylactic acid was synthesized through direct condensation polymerization method so as to reduce the cost and to expand its application. Then polylactic acid microspheres were prepared by solvent evaporation method applied PDLLA as foundation material. In the same way, PDLLA microspheres with imidacloprid or acetamiprid were prepared and the drug-releasing performance of them was analyzed. The results of the research were expanded at the following points:Firstly, polylactic acid was prepared through direct condensation polymerization method. The influence of catalyst types, catalyst quantity, solvent type, solvent dosage, reaction temperature and time on molecular weight were studied. In this study, results showed that the best reaction condition was found:the solution was toluene, the catalyst was p-toluenesulfonic acid using 3%, the polymerization temperature was 140℃, the polymerization time was 29h, the monomer solvent volume ratio of lactic acid and toluene was 1:4, finally sticking in the average molecular weight of polylactic acid reached around 18700.Secondly, polylactic acid microspheres were prepared by conventional solvent evaporation method. In order to gain the optimal process, the influences of different factors on average diameter of microspheres were evaluated. Five factors were considered in the experiment, which were different organic solution, mixture ratio of PDLLA and PVA, PDLLA concentration, surfactant and agitating rates. Experiment results showed that these factors significantly affected the average particle size of the microspheres and the best process to obtain smooth and spherical PDLLA microspheres was found:concentration of PVA was 1.00%, concentration of PDLLA 8.0% and volume ratio of water phase to oil phase 2:1.Finally, PDLLA microspheres with imidacloprid or acetamiprid were prepared by conventional solvent evaporation method. Standard curves of drug, were drawn and the drug-releasing performance of microspheres was analyzed using ultraviolet spectrometry. Experiment results showed that the linearity of imidacloprid or acetamiprid was better in certain rang and that the controlled release effect of polylactic acid microspheres was notable.