Reversible cross-linking, microdomain structure, and heterogeneous dynamics in thermally reversible cross-linked polyurethane as revealed by solid-state NMR.
Reversible cross-linking, microdomain structure, and heterogeneous dynamics in thermally reversible cross-linked polyurethane as revealed by solid-state NMR.
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DOI：
10.1021/jp409893f
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发表时间：
2014-01
期刊：
影响因子：
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通讯作者：
Rongchun Zhang;Shen Yu;Shengli Chen;Qiang Wu;Tiehong Chen;Pingchuan Sun;Baohui Li;D. Ding
中科院分区：
文献类型：
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作者：
Rongchun Zhang;Shen Yu;Shengli Chen;Qiang Wu;Tiehong Chen;Pingchuan Sun;Baohui Li;D. Ding
聚氨酯材料因其化学性质多样、操作相对容易等优点，在工业和日常生活中得到了广泛的应用。在这里，我们专注于一种新型的热可逆的交联型聚氨酯，它具有综合的显著的力学性能，如我们最近的工作(Adv.Mater)所报道的。2013、25、4912)。T2弛豫实验很好地揭示了聚合物的微相分离结构和非均相链段动力学，并首次用于原位监测与Diels-Alder(DA)和RDA(Retro-Diels-Alder)反应相关的可逆交联过程。在T2驰豫测量结果的基础上，我们确定了(R)DA反应的实际温度以及相应的软段运动激活能。此外，还详细讨论了温度和交联剂含量对微区结构和动力学的影响。结果表明，随着温度的升高和交联剂的加入，微相分离得到加强。此外，即使在超过交联键解离的高温下，聚氨酯样品仍然是热稳定的。此外，利用Baum-Pines实验和三脉冲多量子核磁共振实验分别研究了活动链段和刚性链段的非均相结构和动力学。T2弛豫法和多量子核磁共振实验的结果都与PU的宏观力学性能吻合较好。最后，证明了质子T2弛豫法与多量子核磁共振相结合是研究多相聚合物体系非均相结构和动力学的有效方法。
Polyurethane material is widely utilized in industry and daily life due to its versatile chemistry and relatively easy handling. Here, we focused on a novel thermally reversible cross-linked polyurethane with comprehensive remarkable mechanical properties as reported in our recent work (Adv. Mater. 2013, 25, 4912). The microphase-separated structure and heterogeneous segmental dynamics were well revealed by T2 relaxometry experiments, which was also first utilized to in situ monitor the reversible cross-linking associated with Diels-Alder (DA) and retro-Diels-Alder (RDA) reactions. On the basis of T2 relaxometry results, we determined the actual temperature of the (R)DA reaction as well as the corresponding activation energies of the motion of soft segments. Besides, the roles of the temperature and cross-linker contents on the microdomain structure and dynamics are discussed in detail. It is found that the microphase separation is enhanced by the increase of temperature as well as the incorporation of cross-linkers. Also, the polyurethane samples are still thermal-stable even at a high temperature beyond the disassociation of the cross-linkages. Furthermore, Baum-Pines and three-pulse multiple-quantum NMR experiments are utilized to investigate the heterogeneous structures and dynamics of the mobile and rigid segments, respectively. Both the results obtained from the T2 relaxometry and multiple-quantum NMR experiments are in good agreement with the macroscopic mechanical properties of the polyurethane. Finally, it is also well demonstrated that proton T2 relaxometry combined with multiple-quantum NMR is a powerful method to study the heterogeneous structures and dynamics of a multiphase polymer system.