两性磺酸甜菜碱聚合物纳米复合水凝胶的合成、结构和性能的研究
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摘要
两性甜菜碱聚合物水凝胶是一种新型的聚电解质水凝胶,其独特性能使其在药物释放、伤口敷料以及抗蛋白吸附和抗血栓材料等方面表现出了潜在的应用,尤其是合成方法简易并具有独特的高临界溶解温度(UCST)的磺酸甜菜碱聚合物,备受关注。目前所报道的两性磺酸甜菜碱水凝胶大多都是通过化学交联法制备的,其压缩机械性能较差,并且无拉伸力学性能报道,其UCST也很难以调控。因此,改善两性磺酸甜菜碱水凝胶的力学性能,并方便有效地调控其UCST,对构建凝胶与外界环境的应答关系具有重要研究意义。
本研究以提高两性水凝胶的力学性能,并调控其UCST型温敏性为目的,以具有不同结构的两性磺酸甜菜碱单体和中性丙烯酰胺类单体为原料,选用无机粘土为交联剂,采用原位聚合的方法,首次设计并成功制备出了集高强度、UCST型温敏性和耐盐性于一体的新型两性有机/无机纳米复合水凝胶(NC gel),对其合成方法及过程,网络体系结构以及力学性能、温敏性和在不同溶媒中的溶胀消溶胀性能进行了系统的研究。其主要研究内容和结论如下：
1.在氧化还原水溶液体系中,以N,N-二甲基(丙烯酰胺基丙基)氨基丙磺酸(A3)为原料,采用自由基聚合的方法,合成了两性丙烯酰胺类磺酸甜菜碱聚合物(polyA3)及相应的物理交联和化学交联水凝胶。通过关联在O.1M NaCl溶液中测得的特性粘度和分子量首次求得了两性磺酸甜菜碱聚合物Mark-Houwink-Sakurada方程(参数α=0.78),阐述了物理交联水凝胶的形成机理并研究了UCST变化及其影响因素。研究发现,polyA3的物理状态和透明度强烈地依赖于单体浓度和温度。单体浓度为150g/L时,polyA3因正负离子基团间的配对和分子链间的相互缠绕开始形成物理交联水凝胶。PolyA3水溶液凝胶均表现出UCST型温敏性(UCST范围为20-60。C),UCST随单体浓度的增大先升高后降低,存在一最大值,这是分子量和聚合物浓度共同作用的结果。化学交联网络结构的引入和与N-异丙基丙烯酰胺的共聚都使UCST移向低温,甚至最终消失。
2.以两性单体A3、N,N-二甲基(丙烯酰胺丙基)氨基丁磺酸(A4)和3-二甲基-[3-(N-甲基丙烯酰胺)丙基]氨基丙磺酸(M3)为原料,以无机粘土为交联剂,首次成功制备了两性的NC ge1。粘度测试结果表明：两性单体与带净负电荷的粘土之间存在相互作用,高效地抑制了粘土分散液粘度的增大。力学性能和温敏性研究表明：粘土的引入,不仅极大地提高了polyA3和polyA4水凝胶的拉伸力学性能,尤其是A4-NC gel显示出71.3kPa的高拉伸强度和2000%的伸长率；还很好地调控了UCST, polyA3和polyA4水凝胶的UCST分别从23.9℃和100℃降到16.5℃和85℃；而M3-NC gel的力学性能仍很差,UCST也无变化。这归因于由烷基链长度和位阻效应等引起的不同聚合物和粘土片层相互作用程度的差异。
3.为了进一步提高两性NC gel的机械强度和调控其UCST行为,以N,N-二甲基丙烯酰胺(DMAA)作为共聚单体,制备了两性共聚NC gel (A3Dy-NC gel和A4Dy-NC gel)。X射线衍射、透射电子显微镜和傅里叶红外光谱分析证实了聚合物／粘土网络结构的有效形成。力学性能研究发现：因A3和A4聚合物大分子链和粘土相互作用程度的不同,DMAA的加入对它们的力学性能产生了完全不同的影响。A3Dy-NC3gels的拉伸强度和模量随DMAA含量增加而逐渐增大；而A4Dy-NC3gels则先降低后升高,在y=50时出现最小值。温敏性研究发现：改变DMAA含量可以很好地调控两种共聚水凝胶的UCST相变行为,UCST随DMAA含量的增加而移向低温。含10mol%DMAA的两性共聚A3D10-NC3gel同时表现出了高伸展性、强机械性能和UCST型温敏性,成为较理想的材料。在此组成下,通过增大粘土含量,提高交联密度,达到了进一步提高两性水凝胶力学拉伸性能和调控其UCST变化的效果,最大拉伸强度可达200kPa, UCST降至4℃。
4.通过改变总单体浓度(0.1-1M)合成了具有不同聚合物浓度的共聚A3D10-NC-MZ,考察了聚合物浓度对水凝胶形态结构和性能的影响。动弹粘弹性分析表明：A3D10-NC都呈现水凝胶状态,而相应的A3D10-OR则从溶胶逐渐转变为凝胶状态。力学性能研究表明：随着Cp的增加,NC gel的力学性能提高的幅度远远大于OR gel。温敏性研究发现：对于NC gel,在低Cp时,观察不到UCST,随着Cp的增大,UCST出现,并且逐渐移向低温；对于OR gel和共聚物理水凝胶(polyA3D10),则始终能观察到UCST,并且随Cp的增大先升高后降低。基于X射线衍射和透射电子显微镜分析结果,本文提出了共聚NC gel中不同聚合物浓度下聚合物-粘土网络结构模型：即低q时,以分子链附着在粘土片层表面为主,无离子配对；随Cp增大,因粘土片层间相互作用力增强而发生局部聚集；高Cp时,因大分子数目急剧增加,形成了有效的聚合物/粘土网络结构。
5.对两性A3-OR gel和A3-NC gel在不同溶媒中的溶胀收缩行为、透明度和UCST变化进行了探讨。研究发现：在250C水中,OR gel发生收缩现象,NC gel却表现为先溶胀后消溶胀,两者UCST均有所升高。与中性NC gel不同的是,此两性NC gel的最大溶胀度和平衡状态时的含水量均随着n的增大而增大。两性水凝胶在不同浓度的NaCl溶液中也表现出了独特的溶胀收缩行为。在0-0.001M NaCl溶液中,OR gel发生收缩现象,而NC gel表现为溶胀消溶胀现象。在0.001-1M NaCl溶液中,OR gel和NC gel都表现为溶胀现象,溶胀度随着NaCl浓度的增大而增大,完全不同于中性NC gel,表现出较强的耐盐性,有望应用在船舶和医学方面。
总之,具有高拉伸性、UCST型温敏性和耐盐性的新型两性纳米复合水凝胶的成功制备及其可通过改变粘土含量、共聚单体比例和聚合物浓度等实现对结构和性能的调控,为发展此类水凝胶的应用奠定了坚实的理论基础。所发现的因不同结构的聚合物与粘土片层作用力的不同而影响NC gel性能的结果,丰富了有机/无机杂化体系的相互作用理论,也为理解和构建其他体系提供了有益的借鉴和参考。
Hydrogels of zwitterionic betaine polymers are a potential new type of thermosensitive and/or polyelectrolyte hydrogel. They exhibit many potential applications because of their unique properties, such as drug release, wound dressing, and anti-protein adsorption and antithrombotic materials, and so on. They attract much interest, especially the sulfobetaine polymer with simple synthesis method and unique upper critical solution temperature (UCST). Currently, most zwitterionic sulfobetaine hydrogels reported are chemically crosslinked, showing weak compression mechanical property. There is almost no report on their tensile mechanical property. Meanwhile, it is difficult to control their UCST. Therefore, it is very important to improve the mechanical property of zwitterionic sulfobetaine hydrogel and control the UCST effectively for building the response relationship between the gel and external environment.
In this thesis, for the purpose of improving the mechanical property and well-controlling the UCST type thermosensitivity, zwitterionic organic/inorganic nanocomposite hydrogels(NC gels) with high mechanical property, UCST type thermosensitivity and salt tolerance property were successfully synthesized by in situ polymerization, using zwitterionic sulfobetaine monomer with similar structure and nonionic acrylamide monomer in the presence of clay platelets which were used as a crosslinker. The synthesis, network structure, mechanical property, thermosensitivity and the swelling/deswelling behavior in different solvents were studied systematically. The main contents and conclusions on the synthesis and properties of zwitterionic thermosemsitive NC gels with high mechanical property and salt tolerance are as follows:
1. Zwitterionic sulfobetaine acrylamide polymer (poly(N,N-dimethyl (acrylamidopropyl) ammonium propane sulfonate), polyA3) and their physically crosslinked and chemically crosslinked hydrogels were synthesized by free-radical polymerization in an aqueous redox system. The Mark-Houwink-Sakurada equation of zwitterionic sulfobetaine polymer (α=0.78) was firstly obtained by relating the intrinsic viscosity and molecule weight which were measured in O.1M NaCl solution. The formation mechanism of physically crosslinked hydrogel was described. The UCST variations and the factors affecting the UCST were also studied. It was found that the physical state and transparency were strongly dependent on the monomer concentration and temperature. When monomer concentration is150g/L, polyA3began to form the physically crosslinked hydrogels because of the interaction between the negative and positive charged groups and the entanglement of the polymer chain. PolyA3showed the UCST type thermosensitivity (The range of UCST is20-60℃). The variation tendency that UCST increased and then decreased with increasing monomer concentration result from the combine effect of molecular weight and polymer concentration. Both the introduction of chemically crosslinked network and the copolymerization with N-isopropylacrylamide (NIPA) decreased the UCST.
2. Zwitterionic sulfobetaine nanocomposite gel with UCST type thermosensitive property was firstly successfully synthesized by in situ free-radical polymerization of zwitterionic lfobetaine monomers(A3, A4, M3) in the presence of exfoliated clay platelets in an aqueous redox system. Viscosity test showed that the viscosity increase of the clay dispersion was depressed owing to the interaction between zwitterionic monomers and clay. Mechanical property test indicated that the introduction of clay improved the tensile strength of polyA3gel and polyA4gel greatly. Especially, A4-NC gel showed the maximum tensile strength (71.3kPa) and2000%elongation. The UCST was also well controlled. The UCST of polyA3gel and polyA4gel decreased from23.9℃and100℃to16.5and85℃, respectively. However, for M3-NC gel, the tensile strength was still very weak and the UCST did not change at all. These can be attributed to the interaction difference between the different polymers and clay platetlets casused by the length of alkyl chain and steric hindrance effect.
3. In order to further improve the mechanical property and control the UCST of the zwitterionic NC gels, copolymeric zwitterionic NC gel (A3D7-NC gel and A4Dy-NC gel) was prepared successfully using N,N-dimethylacrylamide (DMAA) as comonomer. The formation of polymer/clay network structure was confirmed by XRD, TEM and FTIR. The tensile strength measurement indicated that the introduction of DMAA had a different effect on their properties, as a result of the difference of interaction between the A3and A4polymer chains and clay. The tensile strength and modulus of A3Dy-NC3gels increased with increasing DMAA content. As for A4Dy-NC3gels, the tensile strength decreased first and then increased, showing a minimum at y=50. The thermosensitivity test showed that UCST shifted to low temperature with increasing DMAA content. So the UCST phase transition can be well controlled by altering DMAA content. It is found that the A3D10-NC3gel with10mo1%DMAA exhibited highly stretchable and mechanically tough properties, and UCST phase transition, becoming an ideal hydrogel material. At this molar ratio, increasing the clay content further improved the tensile strength and controlled the UCST. The tensile strength was up to200kPa and UCST decreased to4℃.
4. Zwitterionic copolymeric A3D10-NC-MZ gels with different polymer concentrations were synthesized by altering the total monomer concentration (0.1-1M). The effects of polymer concentration on the structure and property of hydrogel were discussed. Dynamic viscoelasticity analysis indicated that A3D10-NC were gel state, while A3D10-OR were gradually changed from sol to gel. Mechanical property of NC gel and OR gel showed that as Cp increased, the improvement of the tensile strength for NC gel is much larger than OR gel. For NC gel, UCST was not observed at low Cp; UCST appeared and shifted to low temperature with increasing Cp. For OR gel and copolymeric physical gel (polyA3D10), UCST always can be observed and increased first and then decreased with increasing Cp. Based on the results of TEM and XRD, the model of polymer-clay network structure at different polymer concentration in the copolymeric hydrogel was proposed: polymer chain attached to the surface of clay platelets at low Cp; aggregation of clay platelets occurred with increasing Cp; polymer/clay network structure formed at high Cp.
5. The swelling/deswelling behaviour, transparency change and UCST variation of A3-OR gel and A3-NC gel in different solvents were investigated. It indicated that in water at25℃, A3-OR gel deswelled, while A3-NC gel first swelled and then deswelled. The UCST of them increased. The difference from the nonionic NC gel is that both the maximum degree of swelling and water content at equilibrium state of A3-NC gel increased with increasing n. Zwitterionic hydrogel showed unique swelling/deswelling in NaCl solution with different concentrations. At0-0.001M NaCl solution, OR gel deswelled while NC gel swelled first and then deswelled. At0.001-1M NaCl solution, both OR gel and NC gel swelled and the degree of swelling increased with increasing NaCl concentration, which is very different from the nonionic NC gel. They shows the strong salt tolerance propery.
In conclusion, the new zwitterionic nanocomposite hydrogel with high tensile strength, UCST themosensitivity and salt tolerance has been synthesized successfully, and the structure and property of zwitterionic NC gels were well controlled by altering polymer concentration and clay content. All these laid a solid theoretical foundation for the development of such applications hydrogel. The results that the difference interaction between polymers with different structures and clay platelets affected the property of NC gels enriched the interaction theory of organic/inorganic hybrid systems, and also provided a useful reference for understanding and building other systems.
本研究以提高两性水凝胶的力学性能,并调控其UCST型温敏性为目的,以具有不同结构的两性磺酸甜菜碱单体和中性丙烯酰胺类单体为原料,选用无机粘土为交联剂,采用原位聚合的方法,首次设计并成功制备出了集高强度、UCST型温敏性和耐盐性于一体的新型两性有机/无机纳米复合水凝胶(NC gel),对其合成方法及过程,网络体系结构以及力学性能、温敏性和在不同溶媒中的溶胀消溶胀性能进行了系统的研究。其主要研究内容和结论如下：
1.在氧化还原水溶液体系中,以N,N-二甲基(丙烯酰胺基丙基)氨基丙磺酸(A3)为原料,采用自由基聚合的方法,合成了两性丙烯酰胺类磺酸甜菜碱聚合物(polyA3)及相应的物理交联和化学交联水凝胶。通过关联在O.1M NaCl溶液中测得的特性粘度和分子量首次求得了两性磺酸甜菜碱聚合物Mark-Houwink-Sakurada方程(参数α=0.78),阐述了物理交联水凝胶的形成机理并研究了UCST变化及其影响因素。研究发现,polyA3的物理状态和透明度强烈地依赖于单体浓度和温度。单体浓度为150g/L时,polyA3因正负离子基团间的配对和分子链间的相互缠绕开始形成物理交联水凝胶。PolyA3水溶液凝胶均表现出UCST型温敏性(UCST范围为20-60。C),UCST随单体浓度的增大先升高后降低,存在一最大值,这是分子量和聚合物浓度共同作用的结果。化学交联网络结构的引入和与N-异丙基丙烯酰胺的共聚都使UCST移向低温,甚至最终消失。
2.以两性单体A3、N,N-二甲基(丙烯酰胺丙基)氨基丁磺酸(A4)和3-二甲基-[3-(N-甲基丙烯酰胺)丙基]氨基丙磺酸(M3)为原料,以无机粘土为交联剂,首次成功制备了两性的NC ge1。粘度测试结果表明：两性单体与带净负电荷的粘土之间存在相互作用,高效地抑制了粘土分散液粘度的增大。力学性能和温敏性研究表明：粘土的引入,不仅极大地提高了polyA3和polyA4水凝胶的拉伸力学性能,尤其是A4-NC gel显示出71.3kPa的高拉伸强度和2000%的伸长率；还很好地调控了UCST, polyA3和polyA4水凝胶的UCST分别从23.9℃和100℃降到16.5℃和85℃；而M3-NC gel的力学性能仍很差,UCST也无变化。这归因于由烷基链长度和位阻效应等引起的不同聚合物和粘土片层相互作用程度的差异。
3.为了进一步提高两性NC gel的机械强度和调控其UCST行为,以N,N-二甲基丙烯酰胺(DMAA)作为共聚单体,制备了两性共聚NC gel (A3Dy-NC gel和A4Dy-NC gel)。X射线衍射、透射电子显微镜和傅里叶红外光谱分析证实了聚合物／粘土网络结构的有效形成。力学性能研究发现：因A3和A4聚合物大分子链和粘土相互作用程度的不同,DMAA的加入对它们的力学性能产生了完全不同的影响。A3Dy-NC3gels的拉伸强度和模量随DMAA含量增加而逐渐增大；而A4Dy-NC3gels则先降低后升高,在y=50时出现最小值。温敏性研究发现：改变DMAA含量可以很好地调控两种共聚水凝胶的UCST相变行为,UCST随DMAA含量的增加而移向低温。含10mol%DMAA的两性共聚A3D10-NC3gel同时表现出了高伸展性、强机械性能和UCST型温敏性,成为较理想的材料。在此组成下,通过增大粘土含量,提高交联密度,达到了进一步提高两性水凝胶力学拉伸性能和调控其UCST变化的效果,最大拉伸强度可达200kPa, UCST降至4℃。
4.通过改变总单体浓度(0.1-1M)合成了具有不同聚合物浓度的共聚A3D10-NC-MZ,考察了聚合物浓度对水凝胶形态结构和性能的影响。动弹粘弹性分析表明：A3D10-NC都呈现水凝胶状态,而相应的A3D10-OR则从溶胶逐渐转变为凝胶状态。力学性能研究表明：随着Cp的增加,NC gel的力学性能提高的幅度远远大于OR gel。温敏性研究发现：对于NC gel,在低Cp时,观察不到UCST,随着Cp的增大,UCST出现,并且逐渐移向低温；对于OR gel和共聚物理水凝胶(polyA3D10),则始终能观察到UCST,并且随Cp的增大先升高后降低。基于X射线衍射和透射电子显微镜分析结果,本文提出了共聚NC gel中不同聚合物浓度下聚合物-粘土网络结构模型：即低q时,以分子链附着在粘土片层表面为主,无离子配对；随Cp增大,因粘土片层间相互作用力增强而发生局部聚集；高Cp时,因大分子数目急剧增加,形成了有效的聚合物/粘土网络结构。
5.对两性A3-OR gel和A3-NC gel在不同溶媒中的溶胀收缩行为、透明度和UCST变化进行了探讨。研究发现：在250C水中,OR gel发生收缩现象,NC gel却表现为先溶胀后消溶胀,两者UCST均有所升高。与中性NC gel不同的是,此两性NC gel的最大溶胀度和平衡状态时的含水量均随着n的增大而增大。两性水凝胶在不同浓度的NaCl溶液中也表现出了独特的溶胀收缩行为。在0-0.001M NaCl溶液中,OR gel发生收缩现象,而NC gel表现为溶胀消溶胀现象。在0.001-1M NaCl溶液中,OR gel和NC gel都表现为溶胀现象,溶胀度随着NaCl浓度的增大而增大,完全不同于中性NC gel,表现出较强的耐盐性,有望应用在船舶和医学方面。
总之,具有高拉伸性、UCST型温敏性和耐盐性的新型两性纳米复合水凝胶的成功制备及其可通过改变粘土含量、共聚单体比例和聚合物浓度等实现对结构和性能的调控,为发展此类水凝胶的应用奠定了坚实的理论基础。所发现的因不同结构的聚合物与粘土片层作用力的不同而影响NC gel性能的结果,丰富了有机/无机杂化体系的相互作用理论,也为理解和构建其他体系提供了有益的借鉴和参考。
Hydrogels of zwitterionic betaine polymers are a potential new type of thermosensitive and/or polyelectrolyte hydrogel. They exhibit many potential applications because of their unique properties, such as drug release, wound dressing, and anti-protein adsorption and antithrombotic materials, and so on. They attract much interest, especially the sulfobetaine polymer with simple synthesis method and unique upper critical solution temperature (UCST). Currently, most zwitterionic sulfobetaine hydrogels reported are chemically crosslinked, showing weak compression mechanical property. There is almost no report on their tensile mechanical property. Meanwhile, it is difficult to control their UCST. Therefore, it is very important to improve the mechanical property of zwitterionic sulfobetaine hydrogel and control the UCST effectively for building the response relationship between the gel and external environment.
In this thesis, for the purpose of improving the mechanical property and well-controlling the UCST type thermosensitivity, zwitterionic organic/inorganic nanocomposite hydrogels(NC gels) with high mechanical property, UCST type thermosensitivity and salt tolerance property were successfully synthesized by in situ polymerization, using zwitterionic sulfobetaine monomer with similar structure and nonionic acrylamide monomer in the presence of clay platelets which were used as a crosslinker. The synthesis, network structure, mechanical property, thermosensitivity and the swelling/deswelling behavior in different solvents were studied systematically. The main contents and conclusions on the synthesis and properties of zwitterionic thermosemsitive NC gels with high mechanical property and salt tolerance are as follows:
1. Zwitterionic sulfobetaine acrylamide polymer (poly(N,N-dimethyl (acrylamidopropyl) ammonium propane sulfonate), polyA3) and their physically crosslinked and chemically crosslinked hydrogels were synthesized by free-radical polymerization in an aqueous redox system. The Mark-Houwink-Sakurada equation of zwitterionic sulfobetaine polymer (α=0.78) was firstly obtained by relating the intrinsic viscosity and molecule weight which were measured in O.1M NaCl solution. The formation mechanism of physically crosslinked hydrogel was described. The UCST variations and the factors affecting the UCST were also studied. It was found that the physical state and transparency were strongly dependent on the monomer concentration and temperature. When monomer concentration is150g/L, polyA3began to form the physically crosslinked hydrogels because of the interaction between the negative and positive charged groups and the entanglement of the polymer chain. PolyA3showed the UCST type thermosensitivity (The range of UCST is20-60℃). The variation tendency that UCST increased and then decreased with increasing monomer concentration result from the combine effect of molecular weight and polymer concentration. Both the introduction of chemically crosslinked network and the copolymerization with N-isopropylacrylamide (NIPA) decreased the UCST.
2. Zwitterionic sulfobetaine nanocomposite gel with UCST type thermosensitive property was firstly successfully synthesized by in situ free-radical polymerization of zwitterionic lfobetaine monomers(A3, A4, M3) in the presence of exfoliated clay platelets in an aqueous redox system. Viscosity test showed that the viscosity increase of the clay dispersion was depressed owing to the interaction between zwitterionic monomers and clay. Mechanical property test indicated that the introduction of clay improved the tensile strength of polyA3gel and polyA4gel greatly. Especially, A4-NC gel showed the maximum tensile strength (71.3kPa) and2000%elongation. The UCST was also well controlled. The UCST of polyA3gel and polyA4gel decreased from23.9℃and100℃to16.5and85℃, respectively. However, for M3-NC gel, the tensile strength was still very weak and the UCST did not change at all. These can be attributed to the interaction difference between the different polymers and clay platetlets casused by the length of alkyl chain and steric hindrance effect.
3. In order to further improve the mechanical property and control the UCST of the zwitterionic NC gels, copolymeric zwitterionic NC gel (A3D7-NC gel and A4Dy-NC gel) was prepared successfully using N,N-dimethylacrylamide (DMAA) as comonomer. The formation of polymer/clay network structure was confirmed by XRD, TEM and FTIR. The tensile strength measurement indicated that the introduction of DMAA had a different effect on their properties, as a result of the difference of interaction between the A3and A4polymer chains and clay. The tensile strength and modulus of A3Dy-NC3gels increased with increasing DMAA content. As for A4Dy-NC3gels, the tensile strength decreased first and then increased, showing a minimum at y=50. The thermosensitivity test showed that UCST shifted to low temperature with increasing DMAA content. So the UCST phase transition can be well controlled by altering DMAA content. It is found that the A3D10-NC3gel with10mo1%DMAA exhibited highly stretchable and mechanically tough properties, and UCST phase transition, becoming an ideal hydrogel material. At this molar ratio, increasing the clay content further improved the tensile strength and controlled the UCST. The tensile strength was up to200kPa and UCST decreased to4℃.
4. Zwitterionic copolymeric A3D10-NC-MZ gels with different polymer concentrations were synthesized by altering the total monomer concentration (0.1-1M). The effects of polymer concentration on the structure and property of hydrogel were discussed. Dynamic viscoelasticity analysis indicated that A3D10-NC were gel state, while A3D10-OR were gradually changed from sol to gel. Mechanical property of NC gel and OR gel showed that as Cp increased, the improvement of the tensile strength for NC gel is much larger than OR gel. For NC gel, UCST was not observed at low Cp; UCST appeared and shifted to low temperature with increasing Cp. For OR gel and copolymeric physical gel (polyA3D10), UCST always can be observed and increased first and then decreased with increasing Cp. Based on the results of TEM and XRD, the model of polymer-clay network structure at different polymer concentration in the copolymeric hydrogel was proposed: polymer chain attached to the surface of clay platelets at low Cp; aggregation of clay platelets occurred with increasing Cp; polymer/clay network structure formed at high Cp.
5. The swelling/deswelling behaviour, transparency change and UCST variation of A3-OR gel and A3-NC gel in different solvents were investigated. It indicated that in water at25℃, A3-OR gel deswelled, while A3-NC gel first swelled and then deswelled. The UCST of them increased. The difference from the nonionic NC gel is that both the maximum degree of swelling and water content at equilibrium state of A3-NC gel increased with increasing n. Zwitterionic hydrogel showed unique swelling/deswelling in NaCl solution with different concentrations. At0-0.001M NaCl solution, OR gel deswelled while NC gel swelled first and then deswelled. At0.001-1M NaCl solution, both OR gel and NC gel swelled and the degree of swelling increased with increasing NaCl concentration, which is very different from the nonionic NC gel. They shows the strong salt tolerance propery.
In conclusion, the new zwitterionic nanocomposite hydrogel with high tensile strength, UCST themosensitivity and salt tolerance has been synthesized successfully, and the structure and property of zwitterionic NC gels were well controlled by altering polymer concentration and clay content. All these laid a solid theoretical foundation for the development of such applications hydrogel. The results that the difference interaction between polymers with different structures and clay platelets affected the property of NC gels enriched the interaction theory of organic/inorganic hybrid systems, and also provided a useful reference for understanding and building other systems.
引文
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