Photochemistry in polymer solids: 12. Effects of main-chain structures and formation of hydrogen bonds on photoisomerization of azobenzene in various polymer films
Photochemistry in polymer solids: 12. Effects of main-chain structures and formation of hydrogen bonds on photoisomerization of azobenzene in various polymer films
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聚合物固体中的光化学：12.主链结构和氢键形成对各种聚合物薄膜中偶氮苯光异构化的影响
DOI：
10.1016/0032-3861(93)90680-9
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发表时间：
1993
期刊：
影响因子：
4.6
通讯作者：
I. Mita
中科院分区：
文献类型：
--
作者：
T. Naito;K. Horie;I. Mita
利用偶氮苯的光致异构化反应作为光敏探针，研究了聚合物的自由体积分布以及氢键对自由体积分布的影响。在77-340 K的温度范围内对聚甲基丙烯酸甲酯（PMMA）、聚乙烯醇（PVA）和含偶氮苯分子分散的苯氧基树脂薄膜进行了辐照。随着温度的降低，PMMA中偶氮苯反式异构化的最终顺式异构化分数减小，在相同温度下，其顺式异构化分数比聚碳酸酯中的小。这些差异是由于PMMA的亚甲基主链的局部自由体积波动小于聚碳酸酯的芳族链的自由体积波动。由于PMMA的侧链与主链相比大于聚碳酸酯的侧链，因此主链周围的局部自由体积被侧链填充。因此，偶氮苯在PMMA中的最终顺式分数很小。聚乙烯醇中的最终顺式分数小于聚甲基丙烯酸甲酯中的最终顺式分数。由于聚乙烯醇中聚合物链间的氢键在低温下限制了分子的局部运动，偶氮苯分子被基体聚合物链紧紧抓住，自由体积波动在聚乙烯醇中受到限制。动力学模型考虑的自由体积的局部波动也适用于PMMA，聚乙烯醇和苯氧基树脂的结果，并在这些聚合物中的模型的参数进行了讨论。
The free-volume distribution in various polymers and the effect of hydrogen bonds on the free-volume distribution were examined by using a photoisomerization of azobenzene as a photosensitive probe. Poly(methyl methacrylate) (PMMA), poly(vinyl alcohol) and phenoxy resin films containing molecularly dispersed azobenzene were irradiated over a wide temperature range (77–340 K). The finalcisfraction for thetranstocisphotoisomerization of azobenzene decreases with decreasing temperature in PMMA, and smaller fractions are produced than in polycarbonate at the same temperature. These differences are due to the fact that the local free-volume fluctuation of the methylene main chains of PMMA is smaller than that of the aromatic chains of polycarbonate. Since the side chains of PMMA compared to the main chains are larger than those of polycarbonate, the local free volume around the main chains is filled up by the side chains. Hence, the finalcisfraction of azobenzene in PMMA is small. Furthermore, the finalcisfraction in poly(vinyl alcohol) is smaller than that in PMMA. Since the hydrogen bonds among the polymer chains in poly(vinyl alcohol) restrict the local molecular motion at low temperatures, the azobenzene molecule is tightly seized by the matrix polymer chains and the free-volume fluctuation is restricted in poly(vinyl alcohol). The kinetic model considering the local fluctuation of the free volume was also applied to the results for PMMA, poly(vinyl alcohol) and phenoxy resin, and the parameters for the model in these polymers are discussed.