Effect of molecular rigidity and hydrogen bond interaction on mechanical properties of polyimide fibers

Abstract

Six kinds of polyimide (PI) fibers with different molecular rigidity and hydrogen bond interactions were designed and prepared in order to investigate the relationship between structure and mechanical properties. The rigidity, aggregation structure, fracture morphology, hydrogen bond, and charge transfer (CT) interactions were investigated in detail. Conformational rigidity of six PI fibers were simulated and measured by D-values of energy barrier and bottom in potential energy curves of PI units. Rigid rodlike PI macromolecules tend to pack in order and show better mechanical properties. However, with the increase of D-values, fracture mechanisms change from ductile fracture to brittle fracture. Brittle fracture resulting from high conformational rigidity is adverse to improvement of mechanical properties of PI fibers. Besides, strength of hydrogen bond and CT interactions are characterized by infrared spectroscopy and ultraviolet absorption spectra, respectively. The results indicate that higher interactions lead to higher tensile strength and initial modulus. Finally, PI fibers, which possess moderate conformational rigidity and strong hydrogen bond interactions, exhibit highest tensile strength (1.82 GPa) and initial modulus (85.7 GPa) in six kinds of PI fibers.

Heat‐resistant polyimides with lowCTEand water absorption through hydrogen bonding interactions

“…The mechanical properties of polymer films are also the result of molecular packing. With the increase of rigid units in the main chain, the tensile strength and modulus of the films will be improved, but when the content of rigid units reaches a certain degree, the film will change from ductile fracture to brittle fracture, which can be reflected by the sharp decrease of elongation at break 40 . As shown in Figure S6 and Table 3, the PI films exhibited outstanding mechanical properties with tensile strength from 123 to 238 MPa, tensile modulus from 4.3 to 6.7 GPa, and elongation at break from 4.8% to 22.1%.…”

“…With the increase of rigid units in the main chain, the tensile strength and modulus of the films will be improved, but when the content of rigid units reaches a certain degree, the film will change from ductile fracture to brittle fracture, which can be reflected by the sharp decrease of elongation at break. 40 As shown in Figure S6 and Table 3, the PI films exhibited outstanding mechanical properties with tensile strength from 123 to 238 MPa, tensile modulus from 4.3 to 6.7 GPa, and elongation at break from 4.8% to 22.1%. BI unit was used as the additive of the rigid component, the tensile strength, and modulus of the PABZ-based PI films gradually increased and the elongation at break gradually decreased.…”

Design of a Comprehensive Experiment Based on Polyimide Films

“…图5比较了三种PI薄膜的红外光谱。位于1780 cm −1 和1720 cm −1 的吸收峰分别对应于酰亚胺五元 环中羰基的不对称和对称伸缩振动吸收峰；酰亚胺C-N健的伸缩振动吸收峰位于1380 cm −1 处，酰亚 胺环的弯曲振动吸收峰则位于720 cm −1 处，以上特征峰表明实验成功制备了聚酰亚胺 [6] 。而在3500-3100 cm −1 区间内未观察到明显的羧基、酰胺或者氨基的N-H吸收峰，则说明聚酰胺酸已经全部转化 为聚酰亚胺，亚胺化程度非常高 [7] 。 3.3 PI薄膜的拉伸行为和力学讨论 图6(a)比较了三种PI薄膜的拉伸行为，其中PI-0表现为韧性断裂，PI-10表现为脆性断裂，而PI-5 分子链中刚性二胺PDA和柔性二胺ODA各占一半，两者协同作用，实现了薄膜的断裂机理由脆性向 韧性的转变 [8]…”

Homopolyimides containing both benzimidazole and benzoxazole with highTgand low coefficient of thermal expansion

“…A class of PIs containing benzimidazole (PABZ) units was considered to be a potential candidate material for flexible substrates due to their high T g , low CTE and outstanding heat resistance. [7][8][9][10][11][12][13] In addition to the advantages of rigid rod-like structure, the strong charge-donating proton hydrogen of benzimidazole can easily form intermolecular hydrogen bonding with the carbonyl on imide, resulting in the close molecular packing, [14][15][16][17][18][19][20][21] increasing the T g ($ 400 C) and reducing the CTE (<20 ppm/ C) of the derived PIs.…”