Polyimides are commonly used as primary protective optical fiber coatings for high-temperature applications. However, a number of significant drawbacks such as thermal and hydrolytic instability of polyamiс acid, its incomplete transformation into polyimide, several deposition cycles of the required thickness and insufficient adhesion of polyimide coatings to the surface complicate the manufacture of special optical fibers and their widespread use. In this study we showed the principal possibility of utilizing polyamide-imides (PAIs) as primary protective coatings of high operational reliability. Two series of high-molecular-weight (M_w = 84–365 kDa) and thermostable (T_10% = 490–520 °C) PAIs were synthesized by low temperature polycondensation of terephthaloyl chloride and various tetracarboxylic acid dianhydrides with 9,9-bis(4-aminophenyl)fluorene or 2,2′-bis(trifluoromethyl)benzidine in NMP. Coatings of a thickness of 10–15 μm with good adhesion to the optical fiber were formed from the PAIs solutions in NMP with no any additives and in a single application cycle. Apart from the influence of solution viscosity and drawing parameters on the coating quality, a particular attention was paid to the dependency of the strength and mechanical reliability of the fibers with resulting coatings on the structure and molecular weight of the polymer. It was established that the fibers coated with PAIs prepared from 2,2′-bis(trifluoromethyl)benzidine (M_w = 190–200 kDa) can withstand 3 and 72 h annealing at 350 and 300°С, respectively, retaining >80% of the original strength. Thus, PAIs are considered as a promising candidate for further studies, i.e., for the creation of optical fiber sensors for large-scale applications.

聚酰亚胺通常用作高温应用的主要光纤保护涂层。然而，许多显着的缺点，例如聚酰胺酸的热稳定性和水解稳定性、其不完全转变为聚酰亚胺、所需厚度的多次沉积循环以及聚酰亚胺涂层对表面的附着力不足，使特种光纤的制造及其广泛使用变得复杂。 。在这项研究中，我们展示了利用聚酰胺酰亚胺（PAI）作为高运行可靠性的主要保护涂层的主要可能性。通过对苯二甲酰氯和各种四羧酸二酐与 9,9- 的 低温缩聚反应合成了两个系列的高分子量（ M _w  = 84–365 kDa）和耐热（T _{10% = 490–520 °C）PAI。}双(4-氨基苯基)芴或2,2'-双(三氟甲基)联苯胺的NMP溶液。PAI 溶液在 NMP 中形成，厚度为 10-15 μm，对光纤具有良好的附着力，不含任何添加剂，并且在单个应用周期内形成。除了溶液粘度和拉伸参数对涂层质量的影响外，还特别关注纤维的强度和机械可靠性以及所得涂层对聚合物结构和分子量的依赖性。结果表明，涂​​有由 2,2′-双（三氟甲基）联苯胺（M _w  = 190–200 kDa）制备的 PAI 的纤维可以分别在 350 和 300°С 下承受 3 和 72 小时的退火，保留率 >80%原本的实力。因此，PAI 被认为是进一步研究的有希望的候选者，即用于创建用于大规模应用的光纤传感器。