A series of new fluorinated pyridine-based polyimides (PIs) was synthesized by polycondensation of 4-(4-trifluoromethylphenyl)-2,6-bis(4-aminophenyl)pyridine with various aromatic dianhydrides in N, N-dimethylacetamide (DMAc) via the conventional two-step method. The inherent viscosities of the resulting poly(amic acid)s and PIs were 0.54–0.94 and 0.58–0.88 dLg−1, respectively. The obtained PIs were predominantly amorphous and soluble in polar solvents such as N-methyl-2-pyrrolidone, N, N-dimethylformamide, and DMAc at room temperature or upon heating at 70°C. They also displayed good thermal stability with the glass transition temperature of 324–416°C, the temperature at 5% weight loss of 546–584°C, and the residue of 58–69% at 750°C under nitrogen, as well as outstanding mechanical properties with tensile strengths of 69132 MPa, tensile moduli of 1.1–2.0 GPa, and elongations at break of 7–27%. Meanwhile, these PI films had dielectric constants of 2.95–3.22 (1 MHz), low water uptake 0.44–0.71%, and high optical transparency with the ultraviolet cutoff wavelength in the 388–406 nm range and the wavelength of 80% transparency in the range of 550–680 nm.
Background Threatened preterm labor (TPL) is an important obstetrical challenge. Pregnant women with TPL may develop psychological and physical problems such as mental health disorders, sleep disturbance, and hormonal circadian rhythm disruption. This study aimed to investigate the current state of mental health, sleep quality, and circadian rhythms of cortisol and melatonin secretion in pregnant women with TPL and normal pregnant women (NPW). Methods A prospective observational clinical study was conducted at a maternal and child health hospital in Fuzhou, China, between June and July 2022. A total of 50 women between 32 and 36 weeks of gestation (TPL group, n = 20; NPW group, n = 30) were recruited. Data on anxiety symptom (Zung’s Self-rating Anxiety Scale, SAS), depression symptom (Edinburgh Postnatal Depression Scale, EPDS), subjective sleep quality (Pittsburgh Sleep Quality Index, PSQI) and objective sleep outcomes (measured by actigraphy) of the pregnant women were collected at the time of enrolment. Salivary samples were collected once every 6 h (i.e., at 06:00, 12:00, 18:00, and 00:00) during 2 consecutive days to measure the circadian rhythm of hormone (cortisol and melatonin). Results There were no differences found in the total scores of SAS, EPDS scores, subjective sleep quality between the TPL and NPW groups (P > 0.05). In contrast, significant differences were found in sleep efficiency, total sleep time, wake time after sleep onset, and average awakening time between the groups (P < 0.05). The circadian rhythm of melatonin secretion was disrupted in the TPL group (P = 0.350); however, it was maintained in the NPW group (P = 0.044). The circadian rhythm of cortisol secretion was disrupted in both groups (P > 0.05). Conclusions In the third trimester of pregnancy, women with TPL suffer from poorer sleep quality and disruption of circadian rhythm of melatonin secretion compared with NPW. Nevertheless, there were no differences found in mental health (i.e., anxiety and depression) and circadian rhythm of cortisol secretion. Large-scale studies should be conducted to evaluate these changes in women with TPL. Trial registration The study was registered from Chinese Clinical Trial Registry (Number: ChiCTR2200060674) on 07/06/2022.
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