Efficient Construction of Macromolecular Loop and Study on Its Dynamics

环大分子结构由于其闭环拓扑结构，即没有链端，在基础聚合物化学中获得了越来越多的兴趣。缺乏环聚合物链端所赋予的过量迁移率被认为会影响其溶液和体积性质。环状聚合物的典型合成过程是端官能团聚合物前体在稀释条件下的合环反应。然而，开发一种有效的聚合物环化反应仍然是一个持续的挑战。在本研究中，我们分别在Grubbs催化剂的作用下，通过端基为烯烃的线形聚苯乙烯和4臂星形聚苯乙烯的复分解缩合反应合成了环状聚苯乙烯和8形聚苯乙烯。采用活阴离子聚合技术制备聚合物前驱体，并将其作为复分解缩合反应的底物。通过1H NMR、临界条件液相色谱（LCCC）和MALDI-TOF质谱技术对所制得的环状聚苯乙烯和8形聚苯乙烯进行了明确的表征。虽然在稀释条件下也可以进行复分解反应，但反应浓度应低于0.2 g/L，以80%的选择性得到环状聚苯乙烯，这是相当好的，但与一些常规方法相当。因此，一个有效的环化系统的进一步研究应继续提供足够数量的环状聚合物样品的聚合物动力学研究和显微镜分析。

Cyclic macromolecular architectures have gained increasing interests in fundamental polymer chemistry due to its closed loop topology, i.e., absence of chain ends. The lack of the excess mobility conferred by the chain ends of a cyclic polymer is believed to affect its solution and bulk properties. A typical synthetic procedure for cyclic polymers is a ring-closing reaction of an end-functional polymer precursor under dilution. However, a development of an effective polymer cyclization reaction has still been an ongoing challenge. In this study, we have synthesized cyclic and 8-shaped polystyrenes through the metathesis condensation reaction of linear and 4-armed star-shaped polystyrenes having olefinic end groups, respectively, in the presence of Grubbs catalyst. The polymer precursors were prepared by living anionic polymerization technique and were employed as a substrate of the metathesis condensation reaction. The obtained cyclic and 8-shaped polystyrenes were unequivocally characterized by means of 1H NMR, size-exclusion chromatography (SEC) and liquid chromatography at critical condition (LCCC) as well as MALDI-TOF MS techniques. Although the metathesis reaction proceeded even under the diluted condition, the reaction concentration should be below 0.2 g/L to obtain the cyclic polystyrenes in 80% selectivity, which is rather good but comparable to some conventional methods. Thus, the further investigation of an efficient cyclization system should be continued to provide an enough amount of a cyclic polymer sample for a study of polymer dynamics as well as microscopy analysis.