A thermodynamic study on molecular motion of the peroxide ends of isolated single polymer chains tethered to the surface of poly(tetrafluoroethylene) in vacuo
A thermodynamic study on molecular motion of the peroxide ends of isolated single polymer chains tethered to the surface of poly(tetrafluoroethylene) in vacuo
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DOI：
10.1021/ma9716387
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发表时间：
1998-11-03
期刊：
影响因子：
5.5
通讯作者：
Shimada, S
中科院分区：
文献类型：
--
作者：
Sakaguchi, M;Yamamoto, K;Shimada, S
本文讨论了在真空条件下与聚（PTFE）表面相连的孤立高分子链的过氧化端分子运动的热力学。在真空条件下，PTFE与5种单体在PTFE表面进行嵌段共聚，得到了5种孤立的聚合物单链。共聚聚乙烯（PE）、聚丙烯（PP）、聚异丁烯（PIB）、聚丁二烯（PBD）和聚（甲基丙烯酸甲酯）（PMMA）在其链的自由端具有自由基。末端自由基通过与氧气接触转化为过氧化物自由基。过氧化物自由基被用作标记，用于检测在真空中拴系到PTFE表面的孤立的单个聚合物链的过氧化物末端的分子运动。使用一种新的模型，其中的运动松弛是由于旋转松弛的“rotmer”的“火车尾”（不动的移动）过渡的过氧化物端的孤立的单聚合物链进行了分析。旋转异构体是重复单元中形成孤立的单个聚合物链的最小旋转单元，并且具有降低的分子量（M-ro）。如果尾态的自由旋转旋转分子与尾态的冻结旋转分子的比例可以用具有跃迁自由能的Boltzmann统计表示，则可以估计尾-尾跃迁引起的旋转分子的跃迁焓和跃迁熵。得到了这些热力学值及其与转变温度（T-ro）和M-ro之间的线性关系，而Δ S-ro与T-ro和M-ro都是常数。这些关系被解释为意味着形成孤立的单个聚合物链的旋转异构体不含形成相邻孤立的单个聚合物链的相邻旋转异构体。
A thermodynamic study on the molecular motion of peroxide ends of isolated single polymer chains tethered to the surface of poly(tetrafluoroethylene) (PTFE) in vacuo is discussed. The five kinds of isolated single polymer chains were produced by a block copolymerization of PTFE with five kinds of monomers at the PTFE surface in vacuo. Copolymerized polyethylene (PE), polypropylene (PP), polyisobutylene (PIB), polybutadiene (PBD), and poly(methyl methacrylate) (PMMA) have radicals at the free ends of their chains. The end radicals were converted to peroxide radicals by contact with oxygen. The peroxide radicals were used as labels for detecting the molecular motion of the peroxide ends of isolated single polymer chains tethered to the PTFE surface in vacuo. A "train-tail" (immobile-mobile) transition of the peroxide ends of the isolated single polymer chains was analyzed using a new model in which the motional relaxation is due to the rotational relaxation of a "rotmer". The rotmer is the smallest rotational unit in the repeat unit forming an isolated single polymer chain and has a reduced molecular weight (M-ro). If the ratio of a population of freely rotating rotmers in the tail state to that of frozen rotmers in the train state can be expressed by Boltzmann statistics with transition free energy (Delta G), the transition enthalpy (Delta H-ro) and the transition entropy (Delta S-ro) of rotmers due to the train-tail transition can be estimated. These thermodynamic values and their linear relationships among Delta H-ro, transition temperature (T-ro), and M-ro were found. In contrast, Delta S-ro was constant in relation to both T-ro and M-ro. These relationships were interpreted to mean that the rotmers, which form isolated single polymer chains, are free from the neighboring rotmers which form neighboring isolated single polymer chains.