Aggregation of Ureido-Pyrimidinone Supramolecular Thermoplastic Elastomers into Nanofibers: A Kinetic Analysis
Aggregation of Ureido-Pyrimidinone Supramolecular Thermoplastic Elastomers into Nanofibers: A Kinetic Analysis
复制标题
DOI：
10.1021/ma201303s
复制
发表时间：
2011-09-13
期刊：
影响因子：
5.5
通讯作者：
Meijer, E. W.
中科院分区：
文献类型：
--
作者：
Appel, Wilco P. J.;Portale, Giuseppe;Meijer, E. W.
自互补氢键脲基嘧啶酮（UPy）结构由于具有较高的二聚常数而被广泛应用于超分子聚合物的设计。侧向聚集成纤维结构是通过在低Tg低聚物的UPy端基附近添加脲官能团来实现的，从而产生超分子热塑性弹性体。纤维形成的速率主要取决于UPy单元的五位和六位上的取代基。本文公开了一系列分子在固态下的聚集行为，这些分子具有常用的甲基、光学纯的（S）2，7-二甲基庚基和（S）-1-甲基丙基以及在六位上的外消旋1-乙基戊基。用多种技术，包括SAXS、WAXS、AFM、DSC、IR和CD光谱，研究了从熔体中结晶的速率。结果，阐明了在形成过程中所涉及的不同阶段。聚合物的形成是一个分层的过程，从相分离的熔体与UPy-单元的二聚化开始。对于横向聚集成高长径比纳米纤维，需要未取代的五位和脲官能团。所述双晶形成是伴随着多个叠层的二次成核的ID叠层形成的结果。在纳米纤维内的堆叠到堆叠距离取决于UPy取代基的尺寸，这表明取代基在纳米纤维中的堆叠之间。结果还表明，堆叠和叠层形成被减慢和抑制的六个取代基的分支接近的UPy基序，而立体化学异构体的存在下，进一步抑制这种聚集从熔体。这些对超分子形成动力学行为的详细了解为创造适应性超分子材料铺平了道路。
The self-complementary hydrogen bonding ureido-pyrimidinone (UPy) motif is widely used in the design of supramolecular polymers because of its high dimerization constant. Lateral aggregation into fibrous structures is achieved by the addition of urea functions close to the UPy end group of low-T-g oligomers, yielding supramolecular thermoplastic elastomers. The rate of fiber formation is critically dependent on the substituent at the five- and six-positions of the UPy unit. Here the aggregation behavior in the solid state is disclosed for a series of molecules with the commonly used methyl, the optically pure (S)2,7-dimethylheptyl and (S)-1-methylpropyl, and the racemic 1-ethylpentyl group at the six-position. The rate of nanofiber crystallization from the melt was investigated with a variety of techniques, including SAXS, WAXS, AFM, DSC, IR, and CD spectroscopy. As a result, the different stages involved in the nanofiber formation were elucidated. The nanofiber formation is a hierarchical process starting from the phase-separated melt with the dimerization of the UPy-units. For the lateral aggregation into high aspect nanofibers, both a nonsubstituted five position and urea functionalities are required. The nanofiber formation is the result of ID stack formation accompanied by secondary nucleation of multiple stacks. The stack-to-stack distance within a nanofiber is dependent on the size of the UPy-substituent, which demonstrates that the substituents are in-between the stacks in the nanofibers. The results also demonstrate that stack and nanofiber formation is slowed down and suppressed by a branching of the six-substituent close to the UPy motif, whereas the presence of stereochemical isomers further suppresses this aggregation from the melt. These detailed insights into the kinetic behavior of nanofiber formation pave the way to create adaptable supramolecular materials.