Fractal aggregates of conjugated polymer in solution state
Fractal aggregates of conjugated polymer in solution state
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DOI：
10.1021/la0612769
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发表时间：
2006-12-19
期刊：
影响因子：
3.9
通讯作者：
Chen, Show-An
中科院分区：
文献类型：
--
作者：
Li, Yen-Cheng;Chen, Kuei-Bai;Chen, Show-An
半刚性共轭聚合物由于其独特的电学和光子半导体性质而受到科学和技术的广泛关注。光谱研究表明，即使在大量稀释的情况下，这些聚合物在溶液状态下也会发生链间聚集;然而，这一事件的起源和所得聚集体的结构仍然是有待解决的关键问题。在本研究中，我们揭示了共轭聚合物，聚（2，3-二苯基-5-己基-1，4-苯撑乙烯）（DP 6-PPV），在氯仿和甲苯的溶液中的链间聚集体产生的流体动力学半径为几微米的网络聚集体。小角中子散射（SANS）表明，这些聚集体的内部结构可以用2.2-2.7的质量分形维数来表征。网络在氯仿中是松散的，但变得高度紧凑，在较差的甲苯溶剂，由于严重的节段缔合。提高温度减轻了在甲苯中的链段缔合，同时在很大程度上保留了聚集体的质量分形维数。然而，链间聚集从来没有完全消散的加热，这表明存在两种类型的链段关联具有不同的稳定性。高度稳定的链段缔合既不能被氯仿溶剂化，也不能在甲苯中被热破坏，这归因于用于溶液制备的DP 6-PPV粉末中已经存在的d-d络合物。通过这种复合物牢固地连接的链在溶液中形成网络聚集体，从而降低了聚合物的混合熵。在较差的甲苯溶剂中，预先存在的聚集体内部发生了进一步的链段缔合，使网络更加紧密。这种类型的链段缔合可以通过适度加热来破坏，并且其发生归因于DP 6-PPV的脂肪族侧链对甲苯的亲和力差。
Semirigid conjugated polymers have received much scientific and technological interest due to their unique electrical and photonic semiconducting properties. Spectroscopic studies have indicated that these polymers underwent interchain aggregation in the solution state even at large dilution; however, the origin of this event and the structure of the resultant aggregates remained the crucial issues to be resolved. In the present study, we revealed that the interchain aggregation of a conjugated polymer, poly(2,3-diphenyl-5-hexyl-1,4-phenylenevinylene) (DP6-PPV), in solutions with chloroform and toluene generated network aggregates with the hydrodynamic radii of several micrometers. Small angle neutron scattering (SANS) demonstrated that the internal structure of these aggregates could be characterized by the mass fractal dimensions of 2.2-2.7. The networks were looser in chloroform but became highly compact in the poorer toluene solvent due to severe segmental association. Increasing the temperature alleviated the segmental association in toluene while largely retaining the mass fractal dimension of the aggregates. However, the interchain aggregation was never completely dissipated by the heating, suggesting the existence of two types of segmental association with distinct stability. The highly stable segmental association that could neither be solvated by chloroform nor be disrupted thermally in toluene was attributed to the d-d complex already present in the DP6-PPV powder used for the solution preparation. The chains tied firmly by this complex formed network aggregates in the solution and hence reduced the entropy of mixing of the polymer. In the poorer toluene solvent, further segmental association took place within the preexisting aggregates, making the networks more compact. This type of segmental association could be disrupted by moderate heating, and its occurrence was ascribed to the poor affinity of the aliphatic side chains of DP6-PPV for toluene.