【作者】 杨伟胜；

【导师】 刘晓暄；

【作者基本信息】 汕头大学 ， 应用化学， 2008， 硕士

【摘要】 智能型(环境响应性)水凝胶,是对外界刺激如温度、pH值、溶剂组成、光、电场、化学物质等能产生敏感响应行为的一类水凝胶。N-异丙基丙烯酰胺(NIPAM)是一类及其重要的非离子型丙烯酰胺类单体。聚N-异丙基丙烯酰胺(PNIPAM)的低临界溶解温度接近人的体温(LCST = 33℃),它在药物控释方面具有良好的应用前景。可逆加成裂解链转移聚合(RAFT)是可控/“活性”自由基聚合的一种,适用于单体的范围广和反应条件温和,被广泛用于制备复杂结构的聚合物。本论文主要研究了NIPAM自由基光聚合动力学特征,并研究了PNIPAM水凝胶的光活化RAFT合成及其对温度响应性行为。所得结论对于不同性能的智能型水凝胶的RAFT制备方法提供了重要的理论意义和参考价值。主要工作和结论如下:一、在室温下,以S-正十二烷基-S’-(2-甲基-2-丙酸基)三硫代碳酸酯(DDMAT)为链转移剂、2,4,6-三甲基苯甲酰基二苯基氧化膦(TPO)为引发剂,研究了NIPAM的光聚合动力学。研究结果表明,光引发剂的加入可以缩短聚合反应的引发期、显著加快聚合反应速度。在链转移剂与引发剂的摩尔比为15 : 1和引发剂浓度为0.5 wt%时,三硫代碳酸酯DDMAT调控的NIPAM室温RAFT聚合是一典型的“活性”/可控聚合,聚合反应呈现准一级反应动力学特征,聚合物分子量随转化率线性增加,反应后期分子量分布较窄(PDI = 1.30~1.45)。聚合反应所得均聚物具有优异的扩链性能。二、PNIPAM水凝胶的退溶胀速率慢,但在某些领域如化学阀、人工肌肉,往往需要快速退溶胀的性能。为此,本论文采用RAFT光合成方法制备了一系列的水凝胶:1、分别在高温(50℃)和室温(25℃)下,以DDMAT为链转移剂,进行了NIPAM和N,N’-亚甲基双丙烯酰胺(BIS)的RAFT光共聚合研究,制备了不同结构的PNIPAM功能性水凝胶。研究结果表明,随着DDMAT浓度的增加,失水率明显增加,且高温下(50℃)法制得的PNIPAM凝胶具有更高的失水率。并通过对功能性水凝胶的扩链制备了PNIPAM-g-PNIPAM梳型水凝胶,扩链后的水凝胶退溶胀速率更快。2、用RAFT光合成方法制备了PNIPAM大分子链转移剂,用于制备梳型水凝胶(PNIPAM-g-PNIPAM)。水凝胶网络接枝链的链长和含量影响着水凝胶的溶胀性能和去溶胀性能。根据RAFT光聚合机理,利用水凝胶网络中三硫代碳酸酯基团的活性,对梳型PNIPAM-g-PNIPAM水凝胶进行了扩链,合成了更快速退溶胀的梳型水凝胶。3、聚N,N’-二甲基丙烯酰胺(PDMAA)具有很好的亲水性和生物相容性。本论文利用RAFT光合成方法制备了梳型/多孔PNIPAM-g-PDMAA水凝胶。PDMAA接枝链的存在提高了无孔水凝胶的溶胀比和退溶胀速率,LCST增高;孔结构能大幅度的提高无接枝链水凝胶的溶胀比和退溶胀速率,但没有改变水凝胶的LCST;接枝链的存在并没有提高多孔水凝胶的溶胀比,但提高了LCST,且失水率较低。更多还原

【Abstract】 Responsive hydrogels are sensitive to the external stimulus such as temperature, pH, composition of solution, light, ionic strength, magnetic field, electric field and some biochemical molecules. N-Isopropylacrylamide (NIPAM) is an extremely important nonionic acrylamide monomer. Poly(NIPAM) (PNIPAM) possesses a readily accessible lower critical solution temperature (LCST) of 32℃in water, which is close to human body temperature (37℃) and as such has, for example, been evaluated in drug delivery applications. Reversible addition fragmentation chain transfer (RAFT) polymerization has proven itself to be an extremely versatile controlled/“living”free radical polymerization technique (CLRP). It has been shown to be applicable to the controlled polymerization of a wide-range of monomers, under a wide range of conditions to yield well-defined polymers or copolymers with both low polydispersity and functionalized end group as well as polymers with complex architectures. In this paper, kinetics of RAFT photopolymerization of NIPAM was studied. Using this technique of photo-induced RAFT polymerization, several hydrogels which include PNIPAM hydrogels, PNIPAM-g-PNIPAM and PNIPAM-g-PDMAA comb hydrogels and PNIPAM-g-PDMAA comb/porous hydrogels have been prepared. Their temperature behaviors, swelling ratio and dewelling rate were studied. Obtained conclusions were worth in academic and industrial to synthesize and characterize intelligent hydrogels. The followings are main conclusions of our work:1. In this paper, photo-induced RAFT polymerization of NIPAM were studied in the presence of S-dodecyl-S’-(α,α’-dimethyl-α’’-acetic acid) trithiocarbonate (DDMAT) as a RAFT agent and (2,4,6-trimethylbenzoyl) diphenylphosphine oxide (TPO) as a photoinitiator, at room temperature. The variations factors such as the ratio of chain transfer agent and initiator ([CTA]/[I]) were discussed in the paper, which effects on the monomer conversions and molecular weights of the polymers. Additions of TPO photoinitiator remarkably suppress retardation effect in RAFT process, thus shorten initialization period and accelerate overall RAFT process. The experimental results showed that when [CTA]/[I] was 15:1, [I]/[monomer] was 0.5 wt%, The kinetic characteristic of the living polymerization was evidenced by narrow molecular weight distribution (PDI = 1.30~1.45) , linear increase of molecular weight with increasing conversion, well-controlled molecular weight, and first-order polymerization kinetics. The NIPAM homopolymers prepared by RAFT photopolymerization (PNIPAM-DDMAT) had ability of chains extension.2. The conventional Poly(N-isopylacrylamide) hydrogels take more than several hours to days for completion of volume shrinking, which is the main drawback for their practical usage, such as on–off valves and artificial muscles, and was an important topic to be solved. For resolving this problem, herein, several gels were prepared by reversible addition-fragmentation chain transfer (RAFT) photopolymerization.a. Functional poly(N-isopylacrylamide) hydrogels have been prepared by the technique of photo-induced RAFT polymerization of NIPAM in the presence of DDMAT as a chain transfer agent and N,N’-methylenebisacylamide (BIS) as a cross-linker at different temperatures (50℃and 25℃) respectively. The hydrogels (RAFT gels) synthesized at the same temperatures showed accelerating to shrinking kinetics compared with the hydrogels synthesized by conventional photopolymerization. It could be attributed to the presence of dangling chains mainly caused by DDMAT. The RAFT gels synthesized at 50℃showed more excellent water releasing performance than one synthesized at 25℃. According to the mechanism of RAFT photopolymerization, re-grafting of the hydrogels were studied. It indicated more excellent water releasing performance than before.b. The NIPAM homopolymers (PNIPAM-DDMAT) were prepared by RAFT photopolymerization first. Then PNIPAM-g-PNIPAM comb hydrogels were prepared by photopolymerization in the presence of PNIPAM-DDMAT as a macro-CTA and BIS as a cross-linker. The results showed that the grafting chain amount and length had a significant influence on the deswelling kinetics and swelling ratio of gels. After chain extention of PNIPAM-g-PNIPAM comb hydrogels, gels indicated more excellent water releasing performance than before.c.Poly(N,N`-dimethylacrylamide) (PDMAA) is a kind of polymer with excellent biocompatibility. Firstly, the macro-CTA of PDMAA (PDMAA-DDMAT) were prepared by photo-induced RAFT polymerization. Then PNIPAM-g-PDMAA comb/porous hydrogels were prepared by RAFT photopolymerization in the presence of PDMAA-DDMAT, BIS as a cross-linker and poly(ethylene glycol)(PEG) as a pore-forming agent at 20℃. The grafting chain amount had a significant influence on the gel rapid LCST (lower critical solution temperature), deswelling kinetics and swelling ratio. The formation of a porous structure has been shown to effectively enhance the deswelling rate of PNIPAM hydrogels. But it has no effect on the swelling ratio and deswelling rate of the comb hydrogels.更多还原