| Slow-release and long-acting drug is very important in treatment, which canmaintain the concentration of drug in body fluid for a long time. It would improve thetherapeutic effect and there is no side effect on human body. However, the key of thesystem is preparing carrier material which can make the drug release slowly. Drugcarrier materials include natural polymer materials and synthetic polymer materials.Natural polymer carrier materials usually can not meet application requirementscompletely, so people pay more attention to the synthetic biodegradable polymers.Amphipathy block copolymer can self-assemble into micelles in appropriate solvent,which can be used as transporter, target carrier and "nano micro reactor". It has a verybroad application prospects.In the field of medicine, polylactic acid （PLA） is recognized as the mostpromising biodegradable medical polymer material. In this work, PLA wassynthesized first and then polylactic acid-poly methylmethacrylate-2-dimethylamino ethyl (PLA-b-PDMAEMA) block copolymer wasalso prepared. The macromolecular parameters were characterized by1H-NMRspectroscopy and infrared spectrometer (IR) and its environmental response andself-assembly properties were studied.1. The polylactic acid with appropriate molecular weight for the synthesis ofmacromolecular initiator was prepared by the degradation of high molecular weightpolylactic acid. The mechanism of degradation of polylactic acid, weight loss rate, therelationship between molecular weight and molecular weight distribution and thedegradation time were studied. Meanwhile, the molecular structure and molecularweight of poly lactic acid were characterized, which provided a theoretical basis forthe next step of the reaction. In the degradation process, the PDI remained at around1.25. Through analyzing infrared spectra, it showed that the main way of thedegradation of poly lactic acid is the breakage of ester bonds. The structure and molecular weight of poly lactic acid were investigated and provided a theoreticalbasis for the next step work.2. The poly lactic acid initiator PLA-Br was prepared. The PLA-Br was obtainedby reaction of low molecular weight PLA with BIBB. The structure was investigatedby1H-NMR, and the bromide rate was also measured. Then the factors which mayinfluence the bromide rate was investigated. We fixed reaction time and the ratio of2-bromo isobutyryl bromine/poly lactic acid Molar ratio respectively. When thereaction time is24hours and BIBB: PLA=2:1, the conversion bromine rate of polylactic acid can reach up to79%.3. The PLA-b-PDMAEMA copolymer is prepared and characterized.PLA-b-PDMAEMA was obtained by atom transfer radical polymerization (ATRP) ofDMAEMA. The macromolecular parameters were determined by1H-NMRspectroscopy and infrared spectrometer, and its molecular weight was determined bygel chromatography. The results proved the structure of polymer was the same as thepreconceived structure. We studied the thermal performance, effect of self assemblingproperties, the change of responsiveness and hydrophilic property with the change ofthe environment. The increase of degree of polymerization of PDMAEMA not onlydecreased the crystallization degree of polymer but also made the critical micellconcentration change. In addition, micelle shape of the polymer shows highlypH-dependent. It is ball-like in acidic conditions, and becames long strip shape inneutral environment, and appears like spider’s web in alkaline conditions. |
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