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基于PNIPAM的功能化聚合物微球的设计、制备与性能研究
【作者】 赵辉；
【导师】 张其锦；
【作者基本信息】 中国科学技术大学 ， 高分子化学与物理， 2006， 博士
【摘要】 聚异丙基丙烯酰胺(PNIPAM)是一种温度响应性的聚合物，在大约32℃附近会产生可逆的相转变。在“较低的临界溶液温度”(LCST)以下，因为有水分子和NIPAM基团的强的氢键相互作用，聚合物是水溶性的。升温会破坏氢键而有助于疏水相互作用。当溶液温度到达LCST，聚合物链会从溶解的线团状态转变到不溶的小球状态 基于PNIPAM聚合物的分子设计和PNIPAM微凝胶结构设计的不同，会带来各种新的性质。因此微凝胶的结构设计和共聚物的分子设计一直是研究的热点。借助一些特殊的技术，本论文设计制备了具有新型结构的功能化微凝胶和嵌段聚合物，并检测了它们的性质。 在文献中我们可以看到，虽然基于PNIPAM的核壳粒子已经被报道了很多，但是其结构基本都是疏水性聚合物为核，PNIPAM为壳层。在我们看到的文献范围内，没有见到制备PNIPAM为核而外面包裹着疏水性聚合物的微凝胶粒子的报道。虽然这样的粒子必然在药物释放等方面与前面所述的粒子有很大区别，也可以用于研究PNIPAM链的受限运动。 我们分析其困难在于PNIPAM在常温下是亲水性的，而即使升温后变为疏水性也只是一种弱疏水的聚合物。苯乙烯与甲基丙烯酸甲酯(MMA)之类的强疏水性单体在被加入到PNIPAM种子乳液中去的时候，不会停留在PNIPAM的表面而是会进入到粒子的中心去，于是我们不能得到预期的粒子。 我们使用微波辅助聚合，利用微波反应的高聚合速率解决了这一难题。在微波的辅助下，MMA单体迅速的转变成了聚合物，从而难于再进入PNIPAM的种子内部，只能在其表面沉积下来而形成了粒子的壳。 所得到的粒子具有温度敏感性，可以随温度的变化可以进行可逆的膨胀收缩运动。在5个温度循环中，粒子在42℃时的平均半径为70.8nm而在25℃时的平均半径为83.4nm。在粒子中，PNIPAM的膨胀受到了PMMA外壳的限制。因此它的膨胀因子小于PNIPAM为壳的粒子，只有1.63。对粒子内部结构的细节分析可以看到，粒子核心有一个纯PNIPAM的区域，密度较小。粒子外部是PMMA的区域，密度较大。在它们之间，应该存在PNIPAM和PMMA相互缠绕
【Abstract】 Poly (N-isopropylacrylamide) (PNIPAM) is an responsive polymer which undergoes a temperature-induced, reversible phase transition at approximately 32℃. Below the lower critical solution temperature (LCST), the polymer is soluble in water because of the strong hydrogen bonding between the water molecules and the NIPAM groups. The increase of temperature will disrupt hydrogen bonds and favor hydrophobic interactions. When the temperature of the solution reaches LCST, polymer chains change from the well-dissolved coil state to the less soluble globular state.Different molecular design of PNIPAM-based polymers and structure design of PNIPAM-based colloids will bring new attributes. So the particle design and polymer design continue attracting attentions. Through some special technology, this thesis designed and prepared the functional microgel with new structure and the new block copolymer. The properties of them were measured.Numerous reports described different structures of PNIPAM-based core-shell particles with hydrophobic polymer as core and PNIPAM as shell or NIPAM copolymer as core and PNIPAM as shell. However, as much as we know, little work has been reported regarding particles with PNIPAM as the core and hydrophobic polymer as the shell. Although a study about such a particle is significant, which is helpful to research concerning restricted motions of PNIPAM chains and the drug delivery.It is difficult to prepare this kind of particles by a general seed emulsion polymerization. The problem should be that PNIPAM is the polymer with weak hydrophobicity even when it is in the collapse state. The hydrophobicity of most hydrophobic monomers, such as Styrene or MMA, is stronger than that of PNIPAM. Therefore, when the second monomer was added into system, it would enter the inner part of particles, instead of staying on the surface.We try to use microwave heating polymerization to solve this problem and obtain such particles. Compared with normal heating, microwave heating is