Li Donghan, Yang Chen, Li Ping, Yu Lu, Zhao Shufa, Li Long, Kang Hailan, Yang Feng, Fang Qinghong
College of Materials Science and Engineering, Shenyang University of Chemical Technology, Shenyang 110142, China.
Liaoning Provincial Key Laboratory of Rubber & Elastomer, Shenyang University of Chemical Technology, Shenyang 110142, China.
Polymers (Basel). 2023 Jun 4;15(11):2574. doi: 10.3390/polym15112574.
Functional liquid fluoroelastomers are in high demand in new energy fields. And these materials have potential applications in high-performance sealing materials and as electrode materials. In this study, a novel high-performance hydroxyl-terminated liquid fluoroelastomer (t-HTLF) with a high fluorine content, temperature resistance, and curing efficiency was synthesised from a terpolymer of vinylidene fluoride (VDF), tetrafluoroethylene (TFE), and hexafluoropylene (HFP). A carboxyl-terminated liquid fluoroelastomer (t-CTLF) with controllable molar mass and end-group content was first prepared from a poly(VDF--TFE--HFP) terpolymer using a unique oxidative degradation method. Subsequently, an efficient "one-step" reduction of the carboxyl groups (COOH) in t-CTLF into hydroxyl groups (OH) was achieved via the functional-group conversion method using lithium aluminium hydride (LiAlH) as the reductant. Thus, t-HTLF with a controllable molar mass and end-group content and highly active end groups was synthesised. Owing to the efficient curing reaction between OH and isocyanate groups (NCO), the cured t-HTLF exhibits good surface properties, thermal properties, and chemical stability. The thermal decomposition temperature (T) of the cured t-HTLF reaches 334 °C, and it exhibits hydrophobicity. The oxidative degradation, reduction, and curing reaction mechanisms were also determined. The effects of solvent dosage, reaction temperature, reaction time, and ratio of the reductant to the COOH content on the carboxyl conversion were also systematically investigated. An efficient reduction system comprising LiAlH can not only achieve an efficient conversion of the COOH groups in t-CTLF to OH groups but also the in situ hydrogenation and addition reactions of residual double bonds (C=C) groups in the chain, such that the thermal stability and terminal activity of the product are improved while maintaining a high fluorine content.
功能性液态氟弹性体在新能源领域有很高的需求。并且这些材料在高性能密封材料和作为电极材料方面有潜在应用。在本研究中，由偏二氟乙烯（VDF）、四氟乙烯（TFE）和六氟丙烯（HFP）的三元共聚物合成了一种新型的具有高氟含量、耐高温性和固化效率的高性能羟基封端液态氟弹性体（t-HTLF）。首先使用独特的氧化降解方法由聚（VDF-TFE-HFP）三元共聚物制备了具有可控摩尔质量和端基含量的羧基封端液态氟弹性体（t-CTLF）。随后，通过使用氢化铝锂（LiAlH）作为还原剂的官能团转化方法，实现了t-CTLF中羧基（COOH）向羟基（OH）的高效“一步”还原。由此，合成了具有可控摩尔质量和端基含量以及高活性端基的t-HTLF。由于OH与异氰酸酯基（NCO）之间的高效固化反应，固化后的t-HTLF表现出良好的表面性能、热性能和化学稳定性。固化后的t-HTLF的热分解温度（T）达到334℃，并且表现出疏水性。还确定了氧化降解、还原和固化反应机理。还系统研究了溶剂用量、反应温度、反应时间以及还原剂与COOH含量的比例对羧基转化率的影响。包含LiAlH的高效还原体系不仅可以实现t-CTLF中COOH基团向OH基团的高效转化，还可以实现链中残余双键（C=C）基团的原位氢化和加成反应，从而在保持高氟含量的同时提高产物的热稳定性和末端活性。
