摘要
由于在智能传感和生物医药等领域的应用,近年来光响应聚合物备受关注。最近,我们课题组设计合成了一种环缩醛键接生色基团的新型光敏聚合物,该聚合物具有独特的光化学调控机制,即能够通过调节肉桂基的Z-异构化程度来调控环缩醛的价键稳定性。为进一步将其应用于药物控释材料,我们仍需优化该光敏聚合物的分子结构。本论文着重探讨了环缩醛衍生光敏聚合物的光致异构行为和水解行为的分子结构依赖性。本论文采用可见光活化室温RAFT聚合,设计合成了结构精确的光敏聚合物聚5-乙基-5-甲基丙烯酰氧甲基-2-苯乙烯基-[1,3]二氧环己烷(PEMSD)禾(?)聚5-乙基-5-甲基丙烯酰氧甲基-2-p-甲氧基苯乙烯基-[1,3]二氧环己烷(PEMpMSD),同时采用热引发RAFT聚合合成了聚5-乙基-5-甲基丙烯酰氧甲基-2-o-甲氧基苯乙烯基-[1,3]二氧环己烷(PEMoMSD)。研究结果表明,光敏单体的可见光活化室温RAFT聚合具有“活性”/可控特征；生色基团苯环甲氧基取代,提高了光敏单体的聚合反应活性。该类光敏聚合物的光致异构化过程具有明显的分子结构依赖性。苯环邻位甲氧基取代,显著提高聚合物中肉桂基的光致异构化程度；而苯环对位甲氧基取代,导致其光致异构化程度的提高不明显。进一步研究表明,该类光敏聚合物的水解过程同样具有明显的分子结构依赖性。肉桂基苯环对位甲氧基取代,显著加速聚合物中E-肉桂基邻近环缩醛的水解过程,其Z-生色团邻近环缩醛的水解也明显快于相应未取代的。而苯环邻位甲氧基取代,仅能加速E-肉桂基邻近环缩醛的水解过程,而其Z-肉桂基邻近环缩醛的水解速率与相应未取代的基本一致。肉桂基苯环的邻位甲氧基取代,显著拓宽了光控水解过程的调控幅度。
Photoresponsive polymers are of great importance bcause of their wide potential applications for smart materials and biomedical fields. Recently, our research group designed and synthesized a new type of photosensitive polymer whose chromophores were bound with cyclic acetal linkages. The property of this polymer is that the stability of cyclic acetal linkages could be controlled by adjusting the degree of Z-cinnamyl chromophores via photo-isomerization. Considering the utilization of such photosensitive polymer for the drug delivery application, we should optimize the molecular structure of this photosensitive polymer. This thesis describes the light-switchable hydrolysis of their acid-labile cyclic acetal linkages of photosensitive polymers as the methoxy-substitution of their cinnamyl pendent groups. To this end, the well-defined poly[5-ethyl-5-methacryloyloxymethyl-2-styryl-[1,3]dioxane] (PEMSD) and poly[5-ethyl-5-methacry-loyloxymethyl-2-p-meth-oxystyryl-[1,3]dioxane] (PEMpMSD) were synthesized via visible light activating RAFT polymerization at 25℃, and poly[5-ethyl-5-methacryloyloxymethy1-2-o-methoxystyry1-[1,3]dioxane] (PEMoMSD) was synthesized via conventional RAFT polymerization at 70℃. Kinetic studies indicated the "living'/controlled character of the visible light activating RAFT polymerization, and the pendant methoxy para-substituted chromophore improves the polymerization reactivity of monomer. Photoisomerization behaviors of these photosensitive polymers exhibited strong molecular structure dependence. The pendant methoxy ortho-substituted chromophore remarkably increased the degree of isomerization of E-type chromophores, while methoxy para-substituted chromophore slightly increased the degree of this isomerization. Hydrolysis behaviors of these photosensitive polymers were also found to have strong molecular structure dependence. The introduction of methoxy groups in the para-positions remarkably accelerates the hydrolysis process of cyclic acetal linkages both neighboring E-cinnamyl and Z-cinnamyl chromophores, while in the ortho positions can only accelerate those of neighboring E-cinnamyl chromophores. Moreover, the introduction of methoxy groups in the ortho positions increases the modulating range of this photo-controlling hydrolysis.
引文
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