| Drug release, which controlled by polymer membrane, can not only prolong the interaction time, improve the drug effect, but also decrease the dosage and avoid the side-effect on human beings and environment. Acetamiprid, which has good control of aphid for vegetables and fruit trees, is a pyridines broad-spectrum insecticide. At present, the common formulations of acetamiprid are emulsifiable concentrates (EC) and wettable powder (WP), however, acetamiprid of EC formulation was harmful because it use organic solvents, such as toluene, xylene and so on. So, people, especially from developed countries, have strong restriction when it was used on vegetables and fruit trees. It is very important to study the slow-release pesticide formulations because China is a large agricultural country. In this paper, two kinds of polymer materials were synthesized for drug controlled-release and slow-release. At the first, acetamiprid/urea-formaldehyde resin microcapsules were prepared by in-situ polymerization, and the acetamiprid release through urea-formaldehyde resin envelope. At the second, polystyrene-block-poly (D,L-lactide) (PS-b-PDLLA) diblock copolymer was synthesized by a combination of anionic polymerization of styrene and ring-opening polymerization of D,L-lactide (DLLA). Owing to the degradation of polylactide, the PDLLA chain of the copolymer was etched to form porous membranes, which is expected to be used in drug controlled-release and slow-release.Firstly, acetamiprid microcapsules were prepared by in-situ polymerization using urea-formaldehyde resins as carriers. The effect of preparation conditions, such as the mole ratio of urea and formaldehyde, emulsifying time, acidification time and curing time, on the surface morphology, size distribution, efficiency of drug loading and encapsulation were discussed in detail. The release and storage properties of microcapsules were also studied. The main work and results are as follows:1. The optimum preparation conditions of acetamiprid/urea-formaldehyde resin microcapsules are:the molar ratio of urea and formaldehyde is 1:1.8, emulsifying time 1 h, acidification time 1 h, and curing time 2 h.2. The obtained microcapsules, which prepared by the above conditions, have smooth surface, uniform size 2-3μm, and the efficiency of drug encapsulation is over 60%.3. About 45% of the drug of acetamiprid/urea-formaldehyde resin microcapsules under optimal conditions has been released in a month. Moreover, they still have a complete morphology and are not broken after stored for four months under 60℃or at room temperature. Acetamiprid/urea-formaldehyde resin microcapsules have excellent release properties and storage performance. Secondly, PS-b-PDLLA block copolymer was prepared by a combination of anionic polymerization of styrene and ring-opening polymerization of DLLA. Meanwhile, the preparation method of porous polymer membranes by etching PDLLA was also researched.1. Hydroxyl-terminated polystyrene (PSOH) was obtained by anionic polymerization. PS-b-PDLLA diblock copolymer was successfully synthesized by initiating ring-opening polymerization of DLLA with PSOH as a macroinitiator. The diblock copolymer was characterized by nuclear magnetic resonance imaging (NMR), infrared spectroscopy (IR), gel permeation chromatography (GPC) and differential scanning calorimetry (DSC).2. The obtained block copolymer films were made by solution casting method. Then the phase of copolymer was observed by the phase contrast microscope and compared with the mixture of PS and PDLLA. The results showed that the compatibility of block copolymer was better than the blend, and there was no obvious phase separation.3. The block polymer films were immersed in alkaline solution to etch. Then the morphology of polymer films was characterized by scanning electron microscope (SEM). The results showed that the porous polymer membranes could be obtained by the method of etching, which is expected to be used in drug controlled-release and slow-release. |
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