Su Esra, Bilici Cigdem, Bayazit Gozde, Ide Semra, Okay Oguz
Department of Chemistry, Istanbul Technical University, 34469 Maslak, Istanbul, Turkey.
Department of Physics Engineering, Hacettepe University, 06800 Beytepe, Ankara, Turkey.
ACS Appl Mater Interfaces. 2021 May 12;13(18):21786-21799. doi: 10.1021/acsami.1c03814. Epub 2021 Apr 28.
One of the most fascinating challenges in recent years has been to produce mechanically robust and tough polymers with smart functions such as self-healing and shape-memory behavior. Here, we report a simple and versatile strategy for the preparation of a highly tough and highly stretchable interconnected interpenetrating polymer network (c-IPN) based on butyl rubber (IIR) and poly(-octadecyl acrylate) (PC18A) with thermally induced healing and shape-memory functions. Solvent-free UV polymerization of -octadecyl acrylate (C18A) at 30 ± 2 °C in the presence of IIR leads to IIR/PC18A c-IPNs with sea-island or co-continuous morphologies depending on their IIR contents. The lamellar crystals with a melting temperature of 51-52 °C formed by side-by-side packed octadecyl (C18) side chains are responsible for more than 99% of effective cross-links in c-IPNs, the rest being hydrophobic associations and chemical cross-links. The c-IPNs exhibit varying stiffness (9-34 MPa), stretchability (72-740%), and a significantly higher toughness (1.9-12 MJ·m) than their components, which can be tuned by changing the IIR/PC18A weight ratio. The properties of c-IPNs could also be tuned by incorporating a second, noncrystallizable hydrophobic monomer, namely, lauryl methacrylate (C12M), in the melt mixture. We show that the lamellar clusters acting as sacrificial bonds break at the yield point by dissipation of energy, while the ductile amorphous continuous phase keeps the structure together, leading to the toughness improvement of c-IPNs. They exhibit a two-step healing process with >90% healing efficiency with respect to the modulus and a complete shape-recovery ratio induced by heating above of alkyl crystals. The temperature-induced healing occurs via a quick step where C18 bridges form between the damaged surfaces followed by a slow step controlled by the interdiffusion of C18A segments in the bulk. We also show that the strategy developed here is suitable for a variety of rubbers and -alkyl (meth)acrylates of various side-chain lengths.
近年来，最具吸引力的挑战之一是制备具有机械强度高且坚韧，并具备自修复和形状记忆等智能功能的聚合物。在此，我们报道了一种简单通用的策略，用于制备基于丁基橡胶（IIR）和聚（丙烯酸十八烷基酯）（PC18A）的具有热诱导修复和形状记忆功能的高韧性、高拉伸性的互穿聚合物网络（c-IPN）。在IIR存在下，丙烯酸十八烷基酯（C18A）于30±2℃进行无溶剂紫外聚合反应，根据IIR含量不同，可得到具有海岛或共连续形态的IIR/PC18A c-IPN。由并排排列的十八烷基（C18）侧链形成的熔点为51 - 52℃的层状晶体，占c-IPN中有效交联的99%以上，其余为疏水缔合和化学交联。c-IPN表现出不同的刚度（9 - 34 MPa）、拉伸性（72 - 740%），并且其韧性（1.9 - 12 MJ·m）显著高于其组分，可通过改变IIR/PC18A重量比进行调节。通过在熔融混合物中加入第二种不可结晶的疏水单体甲基丙烯酸月桂酯（C12M），也可以调节c-IPN的性能。我们表明，作为牺牲键的层状簇在屈服点通过能量耗散而断裂，而韧性非晶连续相使结构保持完整，从而提高了c-IPN的韧性。它们表现出两步修复过程，模量的修复效率>90%，并且在烷基晶体熔点以上加热可实现完全形状恢复率。温度诱导的修复通过快速步骤发生，即受损表面之间形成C18桥，随后是由本体中C18A链段相互扩散控制的缓慢步骤。我们还表明，这里开发的策略适用于各种橡胶和不同侧链长度的（甲基）丙烯酸烷基酯。
