【作者】 刘洪亮；

【导师】 柳明珠；

【作者基本信息】 兰州大学 ， 高分子化学与物理， 2010， 博士

【摘要】 本论文以N,N-二乙基丙烯酰胺(DEA)和丙烯酸(AA)分别作为温度敏感性单体和pH值敏感性单体,分别采用致孔技术、相分离技术等物理改性方法和在聚合物网络中引入梳型接枝链等化学改性方法,合成了温度／pH值双重敏感的快速响应聚(N,N-二乙基丙烯酰胺-co-丙烯酸)(P(DEA-co-AA))水凝胶,系统地研究了共聚水凝胶对外界环境变化的刺激响应行为,并在此基础上,通过掺杂多壁碳纳米管(MWCNTs),合成了响应速度快且机械强度较好的复合物水凝胶。此外,还系统地研究了DEA的RAFT聚合反应条件,为以后合成结构可控的PDEA共聚水凝胶奠定了理论基础。取得的主要研究结果有：1、以PEG-6000为致孔剂,采用自由基交联共聚法,通过调控单体的组成,合成了温度／pH值双重敏感的快速响应P(DEA-co-AA)水凝胶,FTIR结果表明,PEG-6000可以通过在碱溶液中浸泡的方法完全去除。对水凝胶溶胀研究的结果表明：(1)调节单体的组成,当AA占单体总量的1.1 wt%时,P(DEA-co-AA)水凝胶的体积相转变温度(VPTT)可达到人体生理温度(37.5℃)附近；(2)由于共聚单体AA含有可解离的羧基,赋予了共聚水凝胶明显的pH值敏感性；(3)P(DEA-co-AA)水凝胶在60℃(高于其VPTT)的二次蒸馏水中的退溶胀速度受PEG-6000加入与否和共聚单体AA的加入量的影响,而20℃(低于其VPTT)时在pH=3.0的酸性介质中的退溶胀行为分为两个阶段；(4)当温度在20℃和60℃之间交替改变时,P(DEA-co-AA)水凝胶具有可逆的脉冲响应行为,而当pH值在3.0和6.9之间交替改变时,P(DEA-co-AA)水凝胶的脉冲响应行为受PEG-6000加入与否和共聚单体AA的加入量的影响。2、以不同浓度的NaCl水溶液为反应介质,采用自由基交联共聚法,合成了一系列温度／pH值双重敏感的P(DEA-co-AA)水凝胶,与在二次蒸馏水中制备的P(DEA-co-AA)水凝胶相比,该凝胶对外界温度和pH值的变化具有相似的响应行为。不同的是,在NaCl水溶液中制备的P(DEA-co-AA)水凝胶对温度和pH值变化具有更快的响应速度,而且响应速度受NaCl水溶液浓度的影响。扫描电子显微镜(SEM)分析结果表明,以NaCl水溶液为反应介质所制备的P(DEA-co-AA)水凝胶具有更大的孔隙率。3、将相分离技术和致孔技术两种物理改性手段相结合,采用两步法制备了温度／pH值双重敏感的快速响应P(DEA-co-AA)水凝胶。溶胀实验结果表明：(1)水凝胶的VPTT只与共聚凝胶中两种单体的组成有关,而与具体的聚合过程无关,即采用一步法和采用两步法制备的共聚水凝胶具有相同的VPTT; (2)由于体系中引入了共聚单体AA,水凝胶在很宽的pH值范围内都具有敏感性,而且两步法制备的水凝胶在高温下和酸性介质中的退溶胀速度更快；(3)溶胀／退溶胀动力学实验表明,两步法中的任何一步对水凝胶的快速响应速度都有重要影响；(4)同一种水凝胶的退溶胀速率明显快于溶胀速率。4、合成了末端带有双键的PDEA大分子单体,并将其与单体DEA、AA自由基交联共聚,制备了具有梳型接枝链的P(DEA-co-AA)水凝胶,采用化学改性方法,从分子水平上对该水凝胶的化学结构进行了改性。对所制备的水凝胶的溶胀能力、退溶胀动力学以及对温度／pH值交替改变的脉冲响应行为进行了研究。结果表明,在低于水凝胶的VPTT时,梳型接枝的P(DEA-co-AA)水凝胶在pH>5.0时具有更大的平衡溶胀比(ESRs);同时在二次蒸馏水中的退溶胀动力学显示,退溶胀速率与退溶胀温度有重要关系。此外,梳型接枝水凝胶对温度的交替改变具有更优越的脉冲响应性能。但是,需要说明的是梳型接枝水凝胶对pH值交替改变的脉冲响应行为较差,几乎是不可逆的。此外,还合成了荧光标记的梳型接枝微凝胶,利用荧光手段对梳型接枝水凝胶的快速响应机理进行了探讨。5、首先合成了乙烯基功能化的MWCNTs,并采用拉曼、FTIR等分析手段对其结构进行了表征。在此基础上,将乙烯基功能化的MWCNTs与DEA、AA交联共聚,制备了MWCNT/P(DEA-co-AA)复合水凝胶,系统地研究了水凝胶的机械强度以及对外界刺激的响应行为和响应速度。研究发现,MWCNT/ P(DEA-co-AA)复合水凝胶与P(DEA-co-AA)水凝胶具有类似的温度／pH值响应行为,但MWCNT/P(DEA-co-AA)复合水凝胶具有更高的弹性模量,同时在高温时(60℃)具有较快的响应速度。此外,对水凝胶溶胀机理的研究表明,MWCNT/P(DEA-co-AA)复合水凝胶和P(DEA-co-AA)水凝胶中水的扩散均遵循Fickian扩散定律。6、通过可逆加成断裂链转移(RAFT)聚合方法,合成了一系列不同分子量的PDEA,系统地研究了反应温度、反应时间、[CTA]0／[I]0等对DEA的RAFT聚合反应的影响,结果表明,二硫代苯甲酸苄酯(BDTB)作为链转移剂可以很好的控制DEA的RAFT聚合,为以后合成结构可控以及响应速度快的PDEA共聚水凝胶奠定了理论基础。更多还原

【Abstract】 In this thesis, thermo-and pH-sensitive poly(N,N-diethylacrylamide-co-acrylic acid) hydrogels with rapid response rates were prepared by radical cross-linked copolymerization. Several strategies, including physical and chemical, were adopted to improve the response rates. Meanwhile, functionalized multi-walled carbon nanotubes (MWCNTs) with vinyl groups were introduced to the gel networks to enhance its mechanical strength. The stimuli responsive properties, the swelling/deswelling kinetics as well as the mechanical properties were investigated in detail. Furthermore, a series of poly(N,N-diethylacrylamide) samples with different molecular weights was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. The reaction conditions such as reaction temperature, reaction time, and [CTA]o/[/]o were studied systematically. The main results are shown as following:1. Thermo-and pH-sensitive P(DEA-co-AA) hydrogels with fast response rates were obtained by using PEG-6000 as a pore-forming agent during polymerization. PEG-6000 can be removed completely by sequential immersed in alkaline buffer solutions and distilled water. The swelling studies show that (1) the volume phase transition temperature (VPTT) of the hydrogels can be modulated to 37.5℃, which is close to human physiological temperature, by changing the amount of AA in the initial total monomers. (2) The hydrogels respond to the pH change by introducing AA into the copolymers. (3) The shrinking process at 60℃(above VPTT) is remarkably influenced by combination of the addition of PEG-6000 and the amount of hydrophilic comonomer (AA). The shrinking behavior in buffer solutions of pH= 3.0 has two stages. (4) The pulsatile swelling behavior in distilled water at temperatures alternating between 20℃and 60℃is remarkably reversible. However, the reversibility behavior of pH-responsive is dependent on the AA amount, and also the network structure of the hydrogel. 2. A series of porous P(DEA-co-AA) hydrogels with thermo-and pH-response was successfully prepared by using NaCl aqueous solution as the reaction medium. In comparison with the conventional P(DEA-co-AA) hydrogels, the P(DEA-co-AA) hydrogels prepared in NaCl solution have the similar temperature and pH sensitivity, but exhibit much faster deswelling response rates to both temperature and pH changes, and the deswelling rates depend on the concentration of NaCl solution. These improved properties are attributed to the porous network structure formed by using NaCl solution as the polymerization/crosslinking medium, a finding that is further confirmed by SEM micrographs.3. Thermo-and pH-sensitive P(DEA-co-AA) hydrogels with fast swelling/deswelling rates were obtained by a two-step copolymerization. The following significant facts are found:(1) the VPTTs of the hydrogels are not dependent on the synthesis procedure of the hydrogels, but the composition of the hydrogels; (2) the hydrogels respond to pH change in a wide range after introducing AA into the copolymers, and the response rates are improved by using the two-step copolymerization; (3) the hydrogels produced by the two-step copolymerization have faster swelling/deswelling rates compared with that by conventional method, and both the two steps are necessary for the fast response rates; (4) the deswelling rates are much faster than the swelling rates, because the diffusion resistance of water is considered to be smaller in the shrinking process than that in the swelling process.4. Thermo-and pH-sensitive comb-type grafted P(DEA-co-AA) hydrogels with different compositions were synthesized by free radical copolymerization. The swelling capacities and the deswelling kinetics as well as their reversibility to temperature and pH changes were examined. At room temperature, hydrogels with comb-type grafted chains exhibited higher equilibrium swelling ratios in both distilled water and higher pH buffer solutions (pH> 5). The deswelling behavior of the hydrogels was dependent on the test temperature. In addition, the pulsatile stimuli-responsive studies showed that the hydrogels with comb-type grafted chains had better thermo-reversibility, which was attributed to the freely mobile grafted chains. Furthermore, the mechanism of the response behavior was studied by using steady state fluorescence anisotropy.5. First, multi-walled carbon nanotubes (MWCNTs) with vinyl groups were prepared and characterized by Ramman and FTIR. Second, dual-stimuli sensitive MWCNT-polymer composite hydrogel was synthesized by copolymerizing DEA, AA and MWCNTs with vinyl groups. The results showed that the composite hydrogel (NCG) had both temperature and pH sensitivity. Particularly, comparing with the normal type hydrogel (NTG), NCG exhibited better mechanical strength, and relatively faster response rates to temperature changes. Moreover, the swelling results showed that both NCG and NTG adopt the same diffusion mechanism (Fickian diffusion mechanism).6. A series of poly(N,N-diethylacrylamide) samples with narrow molecular weight distribution was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. The reaction conditions such as reaction temperature, reaction time, and [CTA]o/[I]o were studied systematically. It was proved that well-defined PDEA could be successfully synthesized by RAFT polymerization, and this work provided a theory basis for the synthesis of well-defined PDEA-based hydrogels with rapid response rates.更多还原