【作者】 任艳蓉；

【导师】 印杰；

【作者基本信息】 上海交通大学 ， 高分子化学与物理， 2010， 博士

【摘要】 环境刺激响应性聚合物是一类能够对外界环境的细微物理或化学变化做出响应,产生相应的物理结构和化学性质变化甚至突变的高分子。近些年来,由于其在生物医药、基因工程、传感器、催化剂载体、分散剂等诸多领域潜在的应用价值受到了广泛的关注。在初期的研究中,多以单一刺激响应性的聚合物为研究对象。但是在实际应用中,外界环境的变化是多样化的,因此多重刺激响应性的聚合物受到越来越多的关注。含聚醚(PEO)成分的刺激响应性聚合物备受瞩目,因为PEO具有高度的亲水性,又能溶于大部分有机溶剂,并具有良好的生物相容性。商业产品Pluronic和Tetronic是目前应用最为广泛的PEO-PPO-PEO嵌段共聚物,但是由于在形成稳定凝胶时需要的聚合物浓度很高,限制了它们在生物医药等方面的应用。接枝型PEO共聚物的性能比线性的PEO嵌段共聚物优异,前者具有更快的响应速度且形成的胶束比较稳定。通过传统自由基聚合方法,以AIBN(偶氮二异丁氰)为引发剂,引发4-乙烯基吡啶(4-VP)和甲基丙烯酰胺封端的PEO大单体(PEO-MA)共聚,得到含有吡啶侧基和PEO侧链的多重响应性共聚物(P4VP-g-PEO)。用变温紫外监测共聚物溶液的浊度(CP)随温度的变化,测定了共聚物在不同pH下的CP,发现共聚物的CP随pH升高或共聚物中PEO的含量减小而降低,因此可以控制外部环境条件或共聚物组成以调节其CP。在不同pH条件下,P4VP-g-PEO均可以在4 oC以内完成相转变。同时,共聚物的CP随溶液中NaCl浓度的增加先减小后增大,而相转变速度则呈现出相反的转变趋势。采用变温核磁技术研究了P4VP-g-PEO在水溶液中的相转变行为,发现在低温低pH时P4VP-g-PEO能够完全溶解于水;增大体系的pH,聚合物中P4VP部分由亲水性变成疏水性,形成以P4VP为内核L100为外壳的胶束。高温下,胶束的L100亲水外壳发生塌陷,胶束间相互缠结形成大尺寸的颗粒,从溶液中析出。透射电镜(TEM)观察到共聚物在pH 5.0、低温下,形成直径约为35-45 nm的胶束,共聚物的支化度越高胶束的尺寸越大;高温时,聚合物形成300-500 nm的大尺寸颗粒,支化度高的共聚物形成的颗粒外形不是很规整,而支化度低的共聚物则形成类似“胶束”结构的颗粒。利用环氧基团与胺基的亲核加成/开环反应,制备出一类新型的多重刺激响应性聚醚胺类聚合物。利用这种新的合成方法,选择不同结构的共聚单体,合成出多嵌段聚醚胺(PEA)、接枝聚醚胺(gPEA)和两亲性聚醚胺(agPEA)。三种聚醚胺对温度、pH和离子强度的变化都很灵敏,在pH 6.0-8.0范围内都可以在3 oC以内完成相转变,含亲水侧链的接枝结构的gPEA具有最快的响应速度。三种聚醚胺的CP均随着共聚物中亲水组分的增加而升高,随体系中pH或离子强度的增加而降低。聚醚胺的相转变速度受体系pH、聚合物结构和组分影响较大,低pH、亲水组分含量较少时,聚醚胺的相转变速度较慢,反之聚醚胺的相转变速度较快;含亲水侧链的聚醚胺相转变速度较快。聚醚胺的浓度对其CP的影响不大,但是对其相转变速度有影响,随聚合物浓度的增加相转变速度加快,当聚合物浓度达到一定浓度后,相转变速度趋于恒定。选用芘做探针,测定了三种聚醚胺的临界胶束浓度(CMC),三种聚醚胺的CMC值均低于31.2×10-6 mol/L,两亲性聚醚胺agPEA的CMC值最小。采用动态光散射(DLS)研究了三种聚醚胺的自组装颗粒大小及其粒径分布。在室温、pH 7.4时,除PEA101形成了140 nm左右的球形胶束且粒径有两种分布,其他聚醚胺都能形成小于40 nm的单分散的胶束。聚醚胺胶束的粒径在6.6 < pH < 7.4范围内发生转变,在低pH条件下,胶束尺寸较大,在高pH时胶束粒径较小。在高于聚醚胺CP的温度下,共聚物则自组装成几个微米的颗粒。采用1H NMR技术研究了三种聚醚胺在不同温度、pH条件下的溶液行为和分子间作用情况发现:低pH时,叔氨基被质子化,聚醚胺各个部分的亲水性都很高;高pH时,叔氨基脱质子化,聚醚胺的亲水性由各个部分的亲水平衡控制;升高温度,PEA和gPEA中PPO的亲水性降低,形成胶束;温度升至相转变点附近时,PEO部分的亲水性也大幅降低。agPEA211对尼罗红和甲基橙都有很好的装载能力,使油溶性的尼罗红可以分散在水中,也可以使极性的甲基橙分散在非极性溶剂甲苯中。两种染料的分散溶液可长时间保存,始终保持良好的稳定性。选用2-甲氨基芘标记聚醚胺,合成出带有芘侧基的pePEA。研究pePEA532在不同pH条件下的荧光光谱发现pePEA532在378、397和419nm处的特征峰随着pH的增加而降低,而478nm处的特征峰随pH的升高略有增强。IE/IM随pH变化曲线表明pePEA532的pH转变在6.0-8.0之间。pePEA共聚物IE / IM随温度的升高有一最大值,根据这个最大值可以确定共聚物的相转变温度。pePEA在低温时,形成纳米胶束,高于其CP时,胶束之间发生缔合,形成可达微米级的大颗粒。pePEA在D2O中的1H NMR谱图揭示出,聚合物分子中PO单元随着温度的升高,疏水性增强,紧缩在自组装颗粒内部,。用pePEA211对MWNT进行非共价改性,使MWNT能在水中稳定的分散。TEM图片揭示出MWNT表面包裹着一层聚合物,聚合物层的厚度约1nm。TGA分析表明复合物中聚合物的含量为20.4 wt%,而且复合后,MWNT依然保持良好的热稳定性。更多还原

【Abstract】 Stimuli-responsive polymers are able to undergo relatively large and abrupt, physical or chemical changes in response to small external changes in the environmental conditions. They are of fundamental importance in many scientific areas and have been proposed for use in a variety of applications such as in drug delivery, biotechnology, sensors, catalyst supports, and dispersants. In the early studies, single stimuli-responsive polymers had attracted considerable attention due to the theory of theirs aqueous solution behavior. However, there are many different stimulis in the practical applications, and the interest in the multi stimuli-responsive polymers has grown greatly. The stimuli-responsive polymers containing poly(ethylene oxide) (PEO) segments have been focused on due to its hydrophilicity, solubility in organic solvents and biocompatibility. Up to now, most polymers containing PEO were synthesized by using PEO macroinitiators or vinyl end-capped PEO macromolecules. These reactive processes are usually multistep, and catalysts or initiators are necessary to these reactions. So it is very important to develop new synthesis ways of stimuli-responsive polymer. In this thesis a novel way was been developed. A new multi-responsive polymer, poly(ether ter-amine) (PEA) were synthesized by nucleophilic addition/ring-opening reaction. These polymers exhibit sharp response to temperature、pH and ionic strength. Some potential applications were also investigated.Multi-stimuli responsive copolymers were prepared by free-radical copolymerization of methacrylamide end-capped PEO macromonomer (PEO-MA) and 4-vinylpyridine (4-VP). The copolymer displayed sharp response to temperature and pH. The more PEO was induced into the macromolecule, the higher lower critical solution temperature (CP) of copolymer was observed. And the CP decreased with increasing pH dure to the deprotonation of the pyridine ring. In addition, the CP of P4VP-g-PEO9 presented a unique phase transition behavior with varying salt concentration, showing a minimum with 1 M NaCl solution at pH 6.0,but itsΔT showed a maximum. 1H NMR spectra data showed that the hydrophobic segment of P4VP formed the core and the hydrophilic PEO side chain composed the corona. The TEM images showed that P4VP-g-PEO formed micelles with a diameter of 35-45 nm at pH 5.0 and room temperature. At high temperature, the copolymer formed mesoglobules with a diameter of 300-500 nm.Three series of PEA, multi-block poly(ether ter-amine) (PEA), grafted poly(ether ter-amine) (gPEA) and amphiphilic poly(ether ter-amine) (agPEA) were successfully synthesized by nucleophilic addition / ring-opening reaction. These poly(ether ter-amine)s exhibit very sharp response to temperature, pH and ionic strength with tunable cloud point (CP). They displayed rapid phase transition withΔT < 3 oC,and gPEA and agPEA have smallerΔTs than PEA. Their CPs increased with increasing the PEO content or decreasing pH, and they presented largeΔTs under low pH and PEO content. The critical micelles concentration (CMC) of these poly(ether ter-amine) was determined by using prene as a fluorescent probe. The CMCs were less than 31.2×10-6 mol/L, and increased with increasing PEO content. The results obtained from TEM and DLS revealed that poly(ether ter-amine)s were dispersed as uniform sized nano-micelles in aqueous at room temperature, which can further aggregate into mesoglobules of complex structure at high temperature (> CP). 1H NMR spectra data showed that the tertiary amino groups undergo different changes at different conditions. At lower pH, the tertiary amino groups were protonized and caused the split of the peaks of its neighboring protons. At higher pH, the tertiary amino groups were deprotonized and do similar inductive effect to its neighboring protons, so these protons peaks associated together and showed a single peak. Increasing temperature, two peaks replaced the single peak, which indicated that the tertiary amino groups exited in two different environments of hydrophilic and hydrophobic phase. In the presence of these obtained agPEAs, hydrophobic dye Nile red can be dispersed into aqueous solution and polar dye methyl orange can be dispersed into non-polar toluene. The agPEAs are expected to be potential in application such as encapsulation and controlled release of drugs, due to their simple synthesis, amphiphility and multi-stimuli response.We further investigated a pyrene-labeled poly(ether ter-amine) (pePEA), which was synthesized by nucleophilic addition / ring-opening reaction of 2-methylamine pyrene and Jeffamine L100 with poly(ethylene glycol) diglycidyl ether. It CP decreased with increasing pH. pePEA formed uniform sized nano-micelles in aqueous at room temperature, which can further aggregated into mesoglobules at high temperature (>CP). The fluoscence intensity of pePEA532 decreased with increasing pH. The ratio of excimer emission intensity to monomer emission intensity (IE/IM) increased at pH 6.0~8.0. IE/IM of pePEA showed a maximum with increasing temperature which can be used to confirm the phase transition temperature. TEM images at pH 7.0 showed that pePEA formed nano-micelles at low temperature and mesoglobules at high temperature. At pH 6.0, pePEA532 formed 200-750 nm micelles, and these micelles were linked by copolymer fiber. 1H NMR spectra data showed that the hydrophobicity of PO units of the macromolecule increased with increasing temperature. These PO units gathered together and formed core of self-assemblies which were wraped by the hydrophilic corona of L100. MWNT was noncovalent functionalized by pePEA211 and the functionalized MWNT can be dispersed well in water. TEM image revealed that pePEA had wrapped the MWNT. TGA data indicated that the complex contained 20.4 wt% pePEA.更多还原