【作者】 陈兆伟；

【导师】 陈明清；

【作者基本信息】 江南大学 ， 化学工程与工艺， 2005， 硕士

【摘要】 在智能高分子材料领域,以N-异丙基丙烯酰胺(NIPA)为单体制备的环境敏感性凝胶日益成为研究的热点。PNIPA凝胶化学结构中同时具有亲水性和疏水性基团,在33℃存在可逆的非连续体积相转变,该温度称为低临界溶解温度(Lower Critical SolutionTemperature, LCST)。凝胶相转变的响应速率是评价其性能的重要参数之一,而传统方法合成的PNIPA凝胶响应速率都较慢。考虑到某些特殊应用,如人工肌肉、生物传感器等,提高凝胶响应速率的研究具有重要的意义。本文首先以两种粒径(0.1mm,3μm)的二氧化硅(SiO2)颗粒为致孔剂,经自由基聚合制备了PNIPA凝胶/致孔剂的复合体,对复合体进行充分的酸处理,可使致孔剂完全溶解,无需其它复杂的手段即得到多孔的PNIPA凝胶。用差示扫描量热仪(DSC)对一系列多孔凝胶的相转变温度进行了表征,均在33℃左右。通过扫描电镜(SEM)观察到多孔凝胶表面具有不同程度的孔洞结构。探讨了各反应因素对凝胶溶胀性能的影响,发现致孔剂的种类及用量对凝胶的溶胀率影响较大;相对于无孔凝胶,多孔凝胶的退胀及再溶胀都具有更快的响应速率。通过引入具有可离子化基团的共聚单体丙烯酸,以粒径3μm的SiO2颗粒为致孔剂,制备了具有温度、pH值双重敏感的多孔P(NIPA-co-AA)共聚凝胶。研究了不同预溶胀历史条件下共聚凝胶的再溶胀动力学。不同溶胀历史对相同共聚组成的P(NIPA-co-AA)凝胶的平衡溶胀率没有影响,但酸性预溶胀的中性再溶胀过程既不符合一级动力学,也不符合二级动力学,而可能是几个连续或协同过程共同作用的结果,其一是一个具有较小速率常数的一级动力学过程,另一为具有两个速率常数的完全的自动加速过程。中性预溶胀的酸性再溶胀出现了明显的Over-shooting (拐点效应),整个过程由两个溶胀-退胀过程组成。研究表明,两种相反溶胀历史下凝胶的溶胀动力学都缘于氢键的作用,其一是氢键动态的解离,另一为氢键动态的形成。以不同分子量的水溶性高分子聚乙二醇(PEG)为广义的致孔剂,制备了多孔的P(NIPA-co-AA)共聚凝胶。通过LLS研究了PEG在反应介质中的聚集状态,探讨了其致孔机理,选定以分子量6000的PEG为较为理想的致孔剂。研究发现,凝胶/致孔剂的复合体仅通过在去离子水中的充分浸渍并不能完全洗去PEG-6000,结合LLS的表征结果,采用将复合体浸渍于pH=9的碱性缓冲液中可使凝胶网络进一步伸展,水分子进入凝胶将残留的致孔剂完全洗去。SEM的观察结果显示凝胶中有非常规则的多孔结构。对该多孔凝胶的温敏性及pH敏感性退胀动力学的研究表明,其pH退胀过程类似于一种脉冲式的释放过程,在药物缓释的初步研究中也证实了该过程的存在,该类凝胶在某些特殊药物的控制释放领域有着潜在的应用前景。更多还原

【Abstract】 In the field of smart polymer materials, environment sensitive hydrogels based on themonomer N-isopropylacrylamide(NIPA) is becoming a research focus. There existsimultaneously hydrophobic and hydrophilic groups in the chemical structure of PNIPAhydrogels which exhibit a sharp volume phase transition in water at about 33℃ and this turningtemperature is called Lower Critical Solution Temperature(LCST). The response rate ofvolume phase transition is one of the most important parameters for appreciating hydrogels’properties. However, hydrogels prepared through conventional methods respond to externalstimuli with a slow rate. Since the rapid response rate is the most essential function for theirapplications including artificial muscle and bio-sensor, the response rate has to be improved. In the first part of this dissertation, PNIPA/porogent hybrids were prepared using SiO2with two different diameters(0.1mm,3μm) as porogents. Porous PNIPA hydrogels wereobtained through just immersing hybrids in the hydrofluoric acid solution for a period of timewithout other treatments. LCST as phase transition temperature of the series of poroushydrogels were determined all at about 33℃. Porous structures with different degree wereobserved via SEM. The effect of each reaction factor on the properties about swelling wasinvestigated and found that the type and amount of porogent displayed a strong influence on theswelling ratio (SR) of porous hydrogels and porous hydrogels had much faster deswelling andreswelling rate compared to conventional ones.Thermal-and pH-sensitive porous P(NIPA-co-AA) hydrogels were synthesized throughintroducing ionizable group at the presence of SiO2 (3μm) as porogents. The re-swellingkinetics of copolymer hydrogels previously soaked under different acidic and neutralconditions were studied. Although different pre-swelling history exhibited no effect on theequilbrium swelling ratio with same composition, the neutral re-swelling kinetics with acidicpre-swelling corresponded to neither first nor second-order kinetics. Mechanically speaking,the sigmoidal kinetics derived from this series of hydrogels might be the result of severalconsecutive and/or simultaneous processes: namely, one that follows a first-order kinetics witha very small rate constant;the second one, an overall auto-catalytic process with its two rateconstants. However, acidic re-swelling kinetics with neutral pre-swelling exhibited an obviousover-shooting effect featured a whole process which included two swelling-deswellingprocesses. It was demonstrated that the re-swelling kinetics with opposite pre-swelling historyboth attributed to the function of hydrogen bonds and one is dynamic disruption of hydrogenbond, and the other is dynamic formation of hydrogen bond.In the last section of this thesis, water-soluble macromolecules poly(ethylene glycol)(PEG)with different molecular weight as a kind of general porogent were used to successfully prepareporous P(NIPA-co-AA) hydrogels. The aggregated state of PEGs was investigated throughLLS so as to explorer their pore-forming mechanism and PEG-6000 was selected as the mostsuitable porogent based on the research above. It was found that PEG-6000 couldn’t be totallywashed out only through long time immersion of hydrogel/porogent hybrid in deionized water.Based on the characterization results derived from LLS, the hydrogel network could be furtherenlarged through immersion in pH=9 alkaline buffer solution so that water molecules couldenter into hydrogel to wash out residual porogent. Regular porous structure could be foundfrom the SEM observation. It was displayed from the investigation of hydrogel’s thermal-andpH-sensitive deswelling that its pH-sensitive deswelling was similar to a pulsed release process.This process was confirmed in the preliminary study of drug controlled release and this type ofhydrogel have a potential application in some special drug release.更多还原