Becher M, Salamanca F M, Valentin J L, Saalwächter K, Rössler E A
Nordbayerisches NMR-Zentrum, Universität Bayreuth, 95447 Bayreuth, Germany.
Institute of Polymer Science and Technology (ICTP)─Spanish National Research Council (CSIC), 28006 Madrid, Spain.
J Phys Chem B. 2025 Jan 23;129(3):1082-1094. doi: 10.1021/acs.jpcb.4c05547. Epub 2025 Jan 10.
Rubbers prepared from technical poly(butadiene) and natural poly(isoprene) are studied by field-cycling (FC) H NMR relaxometry to elucidate the changes of the relaxation spectrum. Starting with the non-cross-linked polymer successively cross-links are introduced via sulfur or peroxide vulcanization. Applying an advanced home-built relaxometer allows one to probe entanglement dynamics in addition to Rouse dynamics. We show that entanglement dynamics evidenced in terms of a characteristic power-law in the NMR susceptibility is still observed with an exponent identical to that in non-cross-linked linear polymers. Yet, the entanglement regime disappears more and more from the accessible frequency window upon increasing the cross-link density and a spectrally enlarged Rouse regime is revealed. Adding a swelling agent, the manifestation of the Rouse and entanglement regimes virtually does not change, yet, the apparent power-law exponents increase. Concomitant multiple-quantum (MQ) H NMR experiments provide information on the structure of the rubber network in terms of the residual dipolar coupling and the fraction of the network defects, i.e., persisting entangled or nonentangled chains, introduced upon cross-linking and swelling.
采用场循环（FC）核磁共振氢谱弛豫测量法研究了由工业聚丁二烯和天然聚异戊二烯制备的橡胶，以阐明弛豫谱的变化。从非交联聚合物开始，通过硫磺或过氧化物硫化依次引入交联。使用先进的自制弛豫仪，除了可以探测Rouse动力学外，还能探测缠结动力学。我们发现，以核磁共振磁化率中的特征幂律表示的缠结动力学，其指数与非交联线性聚合物中的指数相同，仍然可以观察到。然而，随着交联密度的增加，缠结区在可及频率窗口中越来越多地消失，并且揭示了一个频谱扩大的Rouse区。添加溶胀剂后，Rouse区和缠结区的表现几乎没有变化，但是表观幂律指数增加。伴随的多量子（MQ）核磁共振氢谱实验，根据残余偶极耦合以及交联和溶胀时引入的网络缺陷（即持续缠结或未缠结的链）的比例，提供了有关橡胶网络结构的信息。
