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標題: Characterization of Thermo- / pH-Responsive Microgels Prepared by Treatment of Graft Copolymer ( Poly (AAc-co-MEA) / PNIPAAm / PEG ) at High Temperature
接枝共聚合高分子Poly(AAc-co-MEA) / PNIPAAm / PEG高溫製備溫度/酸鹼應答型微米膠粒及性質探討
作者: 李明政
lee, Min cheng
關鍵字: microgel
drug delivery
polymeric particles
出版社: 化學工程學系
摘要: Graft copolymers comprising monomeric units of acrylic acid (AAc) and methacryloyl ethyl acrylate (MEA) as the copolymer backbone and poly (N-isopropylacrylamide) (PNIPAAm) and monomethoxy–poly (ethylene glycol) (mPEG) as grafts were obtained from partial transesterification of poly(N-acryloxysuccinimide) (polyNAS) with 2-hydroxyethyl ethacrylate (HEMA) and aminolysis with semitelechilic PNIPAAm-NH2 and PEG-NH2, respectively, followed by full hydrolysis of the remaining NAS residues into AAc in aqueous phase. The structure of the graft copolymers was established by 1H NMR spectroscopy. The graft copolymers underwent self-aggregation into micelle structure with increasing temperature above their critical micelle temperatures (CMTs) in aqueous phase. Microgels were prepared by treatment of polymer aqueous solutions of 1.0 mg/mL at 90 ℃ for two weeks, followed by radical polymerization of the MEA moieties at 60 ℃ for 48h using ammonium pexodisulfate (APS) as the initiator. The approach to preparing microgels by heating the polymer aqueous solution at 90 ℃ prior to the radical polymerization aims to prevent polymeric micelles from serious aggregation. Extensive extent of intermolecular physical entanglement and hydrogen bond formation, however, led to formation of compact structure of polymeric particles. The microgels exhibited temperature-responsive swelling behavior at low pH. However, reduced response to the temperature changes was observed with increasing pH probably due to the increased degree of ionization of the AAc units and hydrophilicity of polymeric particles.
在本文的接枝型高分子是以poly(acrylic acid) (PAAc)及methacryloyl ethyl acrylate (MEA)的共聚合物為主鏈,側鏈為poly (N-isopropylacrylamide) (PNIPAAm)和 monomethoxy–poly (ethylene glycol) (mPEG),合成具有酸鹼/溫度應答功能膠粒。首先合成poly(N-acryloxysuccinimide) (polyNAS)為主鏈,2-hydroxyethyl methacrylate (HEMA)利用轉酯化反應連接polyNAS主鏈,將PNIPAAm-NH2 and mPEG-NH2以aminolysis反應連接到主鏈上,之後進行NAS的水解反應,得到接枝高分子。初步高分子溶液(1 mg/mL)於60 ℃合成的膠粒,經過升溫測試後於60 ℃下由TEM證實為多核聚集形態,且結構上與同溫下高分子微胞相似,故稱60 ℃合成膠粒為次微胞 (sub micelles)。另以相同濃度,提高分子溶液製備溫度達90 ℃,於60 ℃進行交聯反應。該高溫製備膠粒於低pH時,粒徑隨溫度上升而下降,未產生聚集現象。膠粒成因可能來自於高溫的影響,改變多核的結構,產生fusion的效果,增加高分子鏈纏繞及形成分子內作用力(氫鍵)。另外選擇以有機溶劑以透析方式,解開膠粒高分子鏈段的纏繞或者氫鍵的作用力。發現膠粒經過透析處理後,膠粒在pH 5.0時具有溫度收縮應答行為,及具有可逆的酸鹼的應答。
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