Constructing thermally cross-linkable structures into thermoplastic polymers has emerged as a compelling strategy to enhance flame retardancy. However, the cross-linking reactions are hard to control, leading unexpected deterioration of processability and mechanical properties. Here, we report a novel strategy to modulate cross-linking reactions utilizing intramolecular hydrogen bonding and steric hindrance effects. Taking aromatic Schiff base (SA) as an example, novel monomers SAP and SAPN were designed and synthesized by incorporating phenolic and naphthalene units. As expected, the resultant copolymer PET--SAPN exhibited a 120 °C higher cross-linking temperature compared with that of PET--SA, powering them with great processability. Robust mechanical properties were obtained owing to the enhanced polymerization stability and intramolecular hydrogen bonding of SAPN, as evidenced by the tensile strength of 86.0 MPa for PET--SAPN, 1.6 times to that of pure PET. Additionally, PET--SAPN exhibits the highest fire safety, whose peak heat release rate (pHRR) and maximum smoke density () decreased by 49% and 53%, attributing to enhanced char-forming ability from the cross-linking and the phenolic and naphthalene units in SAPN. Considering these adequate improvements, this study provides a novel strategy for designing “self-cross-linking” flame-retardant polymers with improved processability and fire-safety.

中文翻译：

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通过氢键和空间位阻调整交联温度以获得高性能防火聚合物

在热塑性聚合物中构建可热交联结构已成为增强阻燃性的一项引人注目的策略。然而，交联反应难以控制，导致加工性能和机械性能意外恶化。在这里，我们报告了一种利用分子内氢键和空间位阻效应调节交联反应的新策略。以芳香族席夫碱（SA）为例，通过引入酚和萘单元，设计并合成了新型单体SAP和SAPN。正如预期的那样，所得共聚物 PET--SAPN 的交联温度比 PET--SA 高 120 °C，使其具有出色的加工性能。由于 SAPN 增强的聚合稳定性和分子内氢键，因此获得了强大的机械性能，PET--SAPN 的拉伸强度为 86.0 MPa，是纯 PET 的 1.6 倍。此外，PET--SAPN具有最高的防火安全性，其峰值热释放率（pHRR）和最大烟雾密度（）分别降低了49％和53％，这归因于交联和酚醛树脂增强的成炭能力SAPN 中的萘单位。考虑到这些充分的改进，本研究提供了一种设计具有改进的加工性能和防火安全性的“自交联”阻燃聚合物的新策略。