纳米粒子掺杂离子交联超分子网络的构筑及其在橡胶自修复能力与力学性能之间的平衡构效关系

Constructing a supramolecular network based on ionic cross-linkings is one of the effective methods to realize the self-healing capacity for rubbers. However, the mechanical properties of ionic supramolecular network are unsatisfactory due to the nature of non-covalent interactions, which limits their applications. Incorporation of nano-fillers can effectively enhance the strength of rubbers, but usually accompanied by a sacrifice of self-healing capability due to that the filler system is independent of the reversible supramolecular network. In this project, in-situ reaction of excess metal oxides (or hydroxides) nanoparticles and unsaturated carboxylic acid takes place in rubbers. Ionic cross-linked supramolecular network is obtained by limiting the covalent cross-linking of rubber molecules and allowing the polymerization of in situ formed metal salts of unsaturated carboxylic acid. Because of the natural affinity between ion-rich domains and nanoparticles, the residual nanoparticles participate in formation of a reversible doped ionic supramolecular network, thus having little obstructions on the reconstruction of ionic crosslinks. Meanwhile, the well dispersed residual nanoparticles can tailor the mechanical properties of rubbers by changing the nanoparticles/unsaturated carboxylic acid molar ratios. The formation, evolution, structure and properties of the doped ionic supramolecular network will be studied. The project aims at revealing the symbiotic relationships and interactions between nanoparticles, ionic cross-linkings and rubber molecules and elucidating the structure-effect of doped ionic supramolecular network in balanced self-healing capacity and mechanical performance. Since that the introduction of ionic cross-linkings by polymerization of metal salts of unsaturated carboxylic acid works well on majority of polar and nonpolar rubbers, the construction of ionic supramolecular network will not be limited in the polar rubbers with tedious chemical modifications. Therefore, the project will promote the neofunctionalization of commercial rubbers, which has the scientific and practical significances.

以离子交联为基础构筑超分子网络，是实现橡胶自修复功能的有效手段之一。然而，非共价键的弱相互作用本质决定离子交联超分子网络的力学强度低，应用受到限制。引入纳米粒子可有效改善橡胶力学性能，但其不属于离子交联网络体系，严重降低橡胶的自愈能力。项目拟采用过量金属氧化物（或氢氧化物）纳米粒子与不饱合羧酸在橡胶中原位生成金属盐，通过金属盐聚合引入离子交联的同时，限制橡胶形成连续的共价交联网络，纳米粒子参与构筑成为离子交联超分子网络的一部分以降低对自修复的负面影响，实现橡胶自修复的同时改善力学性能。项目对掺杂离子交联超分子网络的形成与演变、结构与性能进行研究，揭示纳米粒子、离子交联与橡胶分子之间的共生关系与相互作用，阐明掺杂网络与自修复、力学性能的平衡构效关系。由于金属盐聚合引入离子交联对大部分极性、非极性橡胶具有普适性，无需局限极性橡胶的化学改性，因此项目将促进商业化橡胶新功能化，具有科学与现实意义。

橡胶材料经过共价交联后形成不溶不熔的高分子三位网络，其本身不具备自修复功能，再生利用困难。因此，探索新的交联方式实现橡胶材料的自修复功能，使之易于再生利用，成为材料领域的重要课题。目前，基于大部分可逆共价键交换反应设计的橡胶材料，大多需要从基础单元开始设计、合成具有相应官能团的大分子结构来实现，这对于常规商业化橡胶并不适用。在此，我们基于过量纳米粒子与不饱和羧酸原位生成不饱和羧酸金属盐形成的可逆非共价键，在橡胶材料中成功构筑纳米粒子掺杂离子交联超分子网络，在赋予橡胶材料优异的自修复性能的同时，保证了橡胶材料的力学性能。具体的研究内容及成果如下：（1）在橡胶基体中原位生成不饱和羧酸金属盐的时候调控纳米粒子过量，对金属盐的转化率以及金属盐/纳米粒子的原生形貌进行研究。（2）提高过氧化物对二甲基丙烯酸锌（ZDMA）的吸附及其引发橡胶基体中原位生成金属盐的效率。通过降低温度和调控过氧化物硫化剂（DCP）用量，在硫化初期阶段抑制DCP分解产生的自由基数量，同时温度降低减缓橡胶分子间交联反应的速率，以此进一步扩大金属盐捕获自由基的竞争优势。（3）开展橡胶复合材料的自修复机理研究，重点研究内外因素对超分子网络的破坏与重构影响。体系进行了硫化时间-交联程度-自修复-力学性能的演变追踪。（4）基于不饱和羧酸金属盐在其他橡胶基体中聚合后的自修复性能并不理想，我们设计了“母胶”改性的方式。利用甲基丙烯酸（MAA）与天然橡胶（NR）胶乳反应后，获得高粘性 “母胶”，再与其他橡胶基体进行共混，过程中加入纳米ZnO引入离子交联，材料表现出较好的自修复行为，自修复率最高可达到90%。（5）利用羧化纳米微晶纤维素在NR/MAA/ZnO体系中同样构筑了掺杂离子超分子网络。其中羧化纳米微晶纤维素通过羧基参与离子/氢键构筑，在其周围分布较高的离子聚集体从而在提高NR力学强度的同时，并未大幅削弱材料的自修复性能。

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