Studies on Molecular Motion of Oriented Polymer Chains by the Fluorescence Analysis

采用时间分辨荧光衰减法（FD）、时间分辨荧光极化法（FP）等荧光分析方法，研究了聚合物链在不同条件下的动态行为。用FP法研究聚合物链在稀溶液中的局部运动我们制备了不同的聚合物，如聚苯乙烯（PS）、聚甲基丙烯酸甲酯（PMMA），在聚合物链的正中间附着有蒽探针，并测量了聚合物链在亚ns区和ns区键向量的自相关次数。由此可以估计出聚合物链的动态链刚度和运动相关的耦合范围。对于PS链的溶剂效应，我们发现在theta溶剂中，局部运动的弛豫时间比在具有较大局部运动活化能的良好溶剂中要长。我们发现链末端的弛豫时间大约是链中部弛豫时间的2倍。用FP法研究半浓聚合物溶液中PMMA链的弛豫时间随聚合物浓度的增加而增加，但其运动模式几乎不随聚合物浓度的增加而改变。这种行为可以用自由体积理论很好地解释。用PF法评价PMMA立体配合物的扭转刚度我们发现，与单链相比，立体配合物具有很高的扭转常数。利用时间分辨FD分析研究酶的构象变化，阐明了免疫球蛋白和色氨酸酶的酶活性与构象变化之间的关系。聚合物链在剪切应力作用下的分子运动我们可以观察到系统的变化，但目前还不能修正聚合物流动所造成的双折射效应。所以这个问题留给了未来的项目去解决。

Dynamic behavior of polymer chains under various conditions was investigated by the fluorescence analysis such as time-resolved fluorescence decay (FD), time-resolved fluorescence polarization (FP) method, where fluorescent probes were attached to polymer chains.1. Studies of local motion of polymer chains in dilute solution by FP method We prepared various polymers, e. g., polystyrene (PS), poly (methyl methacrylate) (PMMA) having anthracene probe attached just in the middle of polymer chains and measured the auto-correlation times of bond vectors of polymer chains in sub-ns and ns regions. From the results we could evaluated the dynamic chain stiffness and the coupling range of motional correlation of polymer chains. As for the solvent effect for PS chain, we found that the relaxation time of local motion in the theta solvent is longer than that in good solvents accompanying larger activation energies of local motion. We found that the relaxation time of chain ends is ca. two times faster than that of the middle part of the chain.2. Studies of PMMA chain in semi-concentrated polymer solution by FP method We found that the relaxation times increase with the increase of polymer concentrations, but the motional modes scarcely change with the polymer concentrations. The behavior was well explained by the free volume theory.3. 'Evaluation of torsional rigidity of PMMA stereocomplpx by PF method We found that the stereocomplex has very high torsional constant compared with the single chain.4. Studies of conformational change of enzymes by the time-resolved FD analysis For immunoglobulin and tryptophanase, the relations between enzymatic activities and conformational changes were elucidated.5. Molecular motion of polymer chains under shear stress by FP method We could observe the systematic change, but so far we could not correct the effect of birefringence due to polymer flow. So this problem was left unsolved for a future project.