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Analysis of the Local Mobility of RAFT Mediated Poly(acrylic acid) Networks via Low Field 1H‐NMR Techniques for Investigation of the Network Topology
Macromolecular Chemistry and Physics ( IF 2.5 ) Pub Date : 2019-12-09 , DOI: 10.1002/macp.201900387
Federica Cavalli 1 , Christoph Pfeifer 2 , Lukas Arens 2 , Leonie Barner 1, 3 , Manfred Wilhelm 2
Affiliation  

An in‐depth investigation of the network topology for a series of sodium acrylate hydrogels synthesized via conventional free radical polymerization (FRP) and reversible addition–fragmentation chain transfer (RAFT) polymerization is conducted. The role of the RAFT agent on the crosslinking process is demonstrated on a model system upon analysis of the reaction mixture via size‐exclusion chromatography before the gelation point. For a comprehensive study, both the impact of the amount of RAFT agent and of the degree of crosslinking on the microstructure of the final product are systematically investigated. In addition to swelling experiments and oscillatory shear rheology measurements, the resulting networks are analyzed via low‐field proton nuclear magnetic resonance (1H‐NMR) techniques such as transverse relaxation and double‐quantum coherence to evaluate the network mobility, which is then correlated to structural inhomogeneity. A broader mobility distribution is observed for the RAFT mediated networks compared to the FRP samples, which can be assigned to a higher content of dangling ends in the former case. The results are further elaborated to propose a mechanism for network formation in presence of a RAFT agent.

中文翻译:

通过低场1H-NMR技术分析RAFT介导的聚丙烯酸网络的局部迁移性,以研究网络拓扑

对通过常规自由基聚合(FRP)和可逆加成-断裂链转移(RAFT)聚合合成的一系列丙烯酸钠水凝胶的网络拓扑结构进行了深入研究。在胶凝点之前通过尺寸排阻色谱分析反应混合物后,在模型系统上证明了RAFT试剂在交联过程中的作用。为了进行全面的研究,系统地研究了RAFT试剂的量和交联度对最终产品微观结构的影响。除了溶胀实验和振荡剪切流变学测量外,还通过低场质子核磁共振对所得网络进行分析(1H-NMR)技术(例如横向弛豫和双量子相干性)来评估网络迁移率,然后将其与结构不均匀性相关。与FRP样品相比,RAFT介导的网络具有更宽的迁移率分布,在前一种情况下,可以将其分配给较高含量的悬空端。进一步详细阐述了结果,提出了在存在RAFT代理的情况下形成网络的机制。
更新日期:2019-12-09
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