【作者】 陈一；

【导师】 徐伟箭；

【作者基本信息】 湖南大学 ， 化学工程与技术， 2014， 博士

【摘要】 智能凝胶因其独特的性能在生物医药、组织工程、物质识别、化学催化、萃取分离、微通道元件、形状记忆材料及响应性显示元件等领域被广泛应用。但传统有机交联凝胶存在明显缺陷,如机械性能差,响应速率慢等极大的限制了其应用及功能的发挥。因此,关于智能凝胶的研究仍集中于凝胶力学性能、响应速率的改善及功能化的进一步拓宽上。本论文以制备具有快速响应速率、优异力学性能的多响应水凝胶为目标,分别以纳米粘土、笼状硅倍半氧烷等为无机添加物,通过单体选择,结构设计,制备得到了一系列性能优异的多响应性纳米复合凝胶,并对凝胶的合成、结构与性能进行系统研究,取得了如下主要结果。首先,以粘土/PNIPA凝胶为基础制备得到高强度、超快速响应温敏水凝胶。(1)采用冷冻聚合制备了粘土交联PNIPA纳米复合凝胶,通过对冷冻时间的控制,得到了一系列具有不同力学性能与响应速率的凝胶。研究表明,聚合早期即开始冷冻将使凝胶内形成完全的互穿微孔结构,使凝胶具有超快解溶胀速率,可10s内失水90wt%,溶胀速率也大幅提高。但因冷冻而引起的凝胶内有效交联大分子减少导致凝胶强度下降严重。随冷冻时间推后,凝胶结构的完善导致响应速率降低而力学性能提高。(2)以TMOS为前驱体加入NIPA/粘土预聚液中,冷冻聚合得到互穿网络(IPN)凝胶,TMOS在凝胶中原位缩聚形成硅-氧第二网络。SEM和偏光显微镜均直接观测到具有互穿微孔的双网络结构。此IPN结构既保证了PNIPA/粘土网络因冷冻聚合而拥有的超快响应速率,又因第二网络存在而具备优异的机械强度。此外,此凝胶较未加入TMOS凝胶具有更佳的形态稳定性。但因网络密度增加,凝胶溶胀率降低。(3)以棉纤维为原料通过酸降解制备得到纳米纤维素晶须,并将其加入NIPA/粘土预聚液中以后期冷冻聚合法制备得到了纳米纤维素复合凝胶。纳米纤维晶须在凝胶内不同程度结合,对凝胶具有明显的增强效果且有利于响应速率的提高。同时,晶须的增强效果与凝胶溶胀程度有明显依赖关系,即溶胀率越小有利于纤维在凝胶内的结合而提高凝胶强度。其次,制备得到了性能优良的多响应性纳米粘土交联纳米复合凝胶。(1)分别以粘土L-G和粘土L-S为交联剂,以DMAEMA为单体通过自由基聚合制备了pH/温度双响应凝胶。研究表明粘土L-S为交联剂时分散良好,合成凝胶(S-NC凝胶)具有良好成形性和收率。S-NC凝胶拥有显著的双响应性,其性能仍决定于粘土用量。较有机交联凝胶,S-NC凝胶拥有更佳的力学性能和溶胀率,LCST低于40℃接近人体温度,更快的响应速率,且重复溶胀性良好,但其强度及回弹性仍需改善。(2)将羧甲基壳聚糖(CMCS)加入粘土L-S交联PDMAEMA凝胶中制备得到半互穿网络凝胶以改变凝胶的pH响应性并增加凝胶的药物结合点。研究证实CMCS的取代度及加入量对凝胶的pH响应性具有明显影响,尤其是在其等电点附近凝胶溶胀率明显降低,CMCS的聚集也被SEM观察到。以茶碱为目标药物研究了复合凝胶的药物负载及在人体胃、肠环境下的释放,结果表明凝胶对茶碱具有良好的负载及在胃环境下具有更好的药物缓释性。(3)合成了水溶性光响应单体2-[4-(丙烯酰氧基)苯基偶氮]苯甲酸,经紫外光谱表征证实该单体具有快速的紫外光致顺-反异构特性,且在可见光照射下可回复。将此单体作为共聚单体引入PNIPA纳米复合凝胶中,研究表明该凝胶在紫外光照下呈现出小幅溶胀响应性并保持了良好的温度响应性,但溶胀回复较慢,且力学性能下降严重。最后,制备了性能优良的POSS杂化无机纳米复合水凝胶。(1)以八乙烯基POSS(OvPOSS)和BIS为共交联剂,溶液聚合制备了POSS杂化P(NIPA-co-DMAEMA)凝胶。凝胶显示出明显温度/pH双响应性,性能依赖于OvPOSS加入量。经SEM及X衍射表征发现OvPOSS加入量大时将在凝胶中发生一定程度聚集,其与聚合物的相互作用导致凝胶具有更低的LCST及更好的压缩强度。由于POSS在凝胶中形成的微疏水区域导致了凝胶解溶胀速率的提高。但凝胶溶胀率下降且拉伸性能仍有待提高。(2)通过两步法合成了以粘土交联NIPA为第一网络,以OvPOSS交联NIPA为第二网络的互穿网络凝胶,成功实现将POSS引入纳米复合凝胶。此体系中OvPOSS对凝胶性能的影响与(1)中描述基本相似,如随POSS增加,溶胀率减小,解溶胀速率增加,压缩强度提高等。凝胶LCST随OvPOSS增加先降低后略微增加。值得注意的是,杂化凝胶仍保持了纳米复合凝胶较好的韧性,其拉伸强度随OvPOSS增加提高而断裂伸长率降低。(3)基于PDMAEMA粘土交联凝胶仍待提高的强度与回弹性,研究将水溶性POSS八氨基盐酸盐(OA-POSS)引入粘土交联PDMAEMA复合凝胶中,经TEM分析,OA-POSS在凝胶中聚集程度直接依赖于其加入量。较未加入前,凝胶的强度及拉伸回复性提高明显,且LCST略微降低至人体体温范围。凝胶溶胀率在解溶胀及干燥后重复溶胀时候区别明显,显示了此凝胶结构在干燥后的重排。更多还原

【Abstract】 Smart hydrogels have became a hot topic of science research, which have been applied in many fields, like drug release, tissue engineering, special material recognition, chemical catalysis, substance separation, microchannel components, shape memory materials, and stimuli-responsive devices. However, due to the shortcomings of traditional chemical cross-linked hydrogels, such as slow responsive rate, weak mechanical properties etc, most of researches have focused on improving the mechanical properties, response rate and extending the function.In this thesis, the nanosized inorganic clay and POSS were used as additive, through choosing the monomers and designing the structure, a series of nanocomposite hydrogels with excellent properties, fast response rate and multi-responsiveness were prepared. Their synthesis, structure and properties have been systematically investigated. The results and conclusions are as follows:Firstly, the work focused on the further improvement of the response rate and mechanical properties based on PNIPA/clay nanocomposite hydrogels (NC gels).(1) The PNIPA NC gels were prepared by freezing polymerization for improving the response rate. Through the control of the freezing time, the gels with various properties were gotten. Freezing the pre-polymerization solution before the formation of clay-polymer brush makes the gels own absolute interconnect porous structure, and thereby resulting in an ultrarapid deswelling rate, such as losing90wt%of water within10s, while the mechanical strength decreases significantly due to the decrease of the effective crosslinked polymer chains between the clay. With the delay of freezing time, the response rate decreases while the mechanical properties enhances.(2) Based on the results above, the tetramethoxysilane (TMOS) solution were added into the freezing polymerized PNIPA NC gels to form the second-Si-O-network by polycondensation, which was confirmed by SEM, polarizing microscope and TGA analysis. This kind of IPN hydrogels exhibits excellent mechanical properties with very fast response rate. Meantime, comparing the normal NC gels, this IPN gels own better dimensional stability in deswelling process.(3) The cellulose nano-whisker prepared by acid decomposing cotton cellulose was added into the freezing polymerized PNIPA NC gels for reinforcement, the effect of cellulose whisker on the properties of hydrogels with various swelling ratio was investigated detailedly. The results showed that the cellulose interacts in gels, which causes the obvious enhancement and faster response rate, the effect of reinforcement is determined by the swelling ratio of gels and the amount of cellulose directly, the smaller swelling ratio makes the cellulose whisker be closer so as to interact strongly, which results in the significant enhancement of the strength of gels.Secondly, preparing the multi-responsiveness clay cross-linked nanocomposite hydro gels for extending the application of NC gels.(1) The monomer dimethylaminoethyl methacrylate (DMAEMA) was cross-linked by clay L-G and L-S respectively in situ free radical polymerization to prepare nanocomposite gels (named as G-NC gels and S-NC gels). From the analysis of yield, FTIR, X-Ray and SEM, it was proved that the clay L-S is an appropriate crosslinker for preparing PDMAEMA NC gels with better homogeneous and higher yield due to the uniform dispersion of clay in gels. The resulting S-NC gels show obvious temperature and pH double-sensitiveness. Comparing to traditional chemically crosslinked gels, S-NC gels own better mechanical properties and swelling properties, lower LCST than40℃, faster response rate and better repetitive swelling properties.(2) Linear carboxymethyl chistosan (CMCS) was introduced into the PDMAEMA NC gels as semi-IPN gels (C-NC gels) for adding the bonding point of drug. The amount and substitution degree of CMCS makes a significant impact on the pH responsiveness of gels, especially, the swelling ratio decreases considerabley around the isoelectric point of system. In the drug load and release test in simulated human intestinal and stomachic condition by using theophylline as target, the C-NC gels exhibits an excellent load ability and controlled-release in stomachic condition.(3) Water soluble azo monomers [4-(4’-carboxyphenylazo) phenoxy] acrylate (CPA), exhibiting fast UV responsiveness and the recoverability under visible light, was synthesized and used to prepare temperature/UV responsive P(NIPA-co-CPA) NC gels. The gels with high content of CPA exhibit obvious volume shrink under the UV-light, while the temperature responsiveness still is kept well. Meantime, the mechanical properties of gels decrease significantly with the increase of CPA.Thirdly, the POSS hybrid hydrogels were prepared for developing new organic-inorganic hydrogels systems with excellent properties.(1) POSS hybrid P(NIPA-co-DMAEMA) hydrogels with organic-inorganic co-crosslinked networks were synthesized by using both organic cross-linker BIS (N,N’-methylenebis(acrylamide)) and inorganic cross-linker OvPOSS (octavinyl polyhedral oligomeric silsesquioxane). The resulting gels display obvious temperature and pH double responsiveness, OvPOSS particles dispersed in polymer make a dominant effect on the properties of gels. With the increase of OvPOSS, the aggregation of particles on nano or micro-scale happens, which is proved by SEM and X-ray analysis. The increase of OvPOSS leads to the change of gels’properties, such as the lower LCST and better compression strength. Specially, the interconnected microporous structure of gels ascribed to the micro-phase separation results in faster deswelling rate, which makes the gel become attractive. Meanwhile, the swelling ratio and tensile behavior of gels is still need to be improved.(2) OvPOSS particles were incorporated into PNIPA NC gels via a two-step technique. The second PNIPA network crosslinked by OvPOSS was polymerized in the presence of the first clay-PNIPA network. The OvPOSS makes a similar effect on the properties of gels, which is described in (1). In brief, with the increased OvPOSS, the gels show lower swelling ratio, faster deswelling rate and better compression strength, the LCST of gels rise first and then decline slightly. Most importantly, the gels keep the good toughness of NC gels with a higher tensile strength, despite that the elongation at break decreases.(3) For improving the properties of PDMAEMA NC gels, the water-soluble octaammonium-POSS was added into the gels by in situ polymerization. The aggregation of POSS is directly dependent on its content in gels. Comparing to the POSS-free gels, the tensile strength and resilience of gels is improved obviously. Meantime, the gels show lower LCST being closer to the temperature of human body, and higher deswelling rate. Most interestingly, the gels exhibit discriminative reswelling behavior after deswelling and thoroughly drying, which may be attributed to the rearrangement of structure of gels.更多还原