An increasing number of studies have suggested benefits of greenness exposure on mental health. We examined the association between urban greenness and depressive symptoms in adults in the general population living in the seven major cities in Korea (N = 65,128). Using data from the Korean Community Health Survey 2009, depressive symptoms were measured on the Center for Epidemiological Studies Depression Scale (CES-D). Greenness was assessed using Normalized Difference Vegetation Index (NDVI) and land-use data (forest area and forest volume). Logistic regression models were fitted to adjust for potential confounders. Individuals in regions with the highest NDVI (quartile 4) had the lowest odds for depressive symptoms compared to quartile 1, after adjusting for potential confounders (OR = 0.813; 95% CI: 0.747, 0.884). For all greenness indicators except for forest area per district area (%), the highest rate of depressive symptoms was found for the individuals in the lowest quartile of greenness (quartile 1) and the lowest rate of depressive symptoms for those in the highest quartile of greenness (quartile 4). We found an inverse association between urban greenness and depressive symptoms, which was consistent across a variety of greenness indicators. Our study suggests health benefits of greenness and could provide a scientific basis for policy making and urban planning.

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To enhance poor gas selectivity of polyimides based on hexafluoroisopropylidene diphthalic anhydride (6FDA), such as 6FDA-4,4′-hexafluoroisopropylidene diamine (6FDA-6FpDA) and 6FDA-6FpDA:diaminobenzoic acid (6FDA-6FpDA:DABA), membranes were fabricated from their blends with poly(methylmethacrylate) (PMMA). The resulting polyimides formed homogeneous mixtures with PMMA, regardless of the blend compositions. The miscible blends underwent phase separation upon heating due to the lower critical solution temperature phase behavior. The phase separation temperature of the 6FDA-6FpDA/PMMA blend was greater than that of the 6FDA-6FpDA:DABA/PMMA when the composition was fixed. Adding a small amount of PMMA dramatically increased the gas selectivity of the membrane. In addition, the gas selectivity of most blends was better than that of pure PMMA. The membranes showed performance advantages for the tradeoff trend between gas permeability coefficient and selectivity.

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Several blends of polymers that varied concentrations of poly(methyl methacrylate) (PMMA) and polyimides based on 2,2 0 -bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) were prepared in film form by solution casting and using various solvents. The miscibility of the blended films was correlated through a differential scanning calorimeter (DSC), Fourier transform infrared spectroscopy (FTIR), and an image analyzer. DSC thermograms revealed two glass-transition temperatures (T g ) for specimens using tetrahydrofuran (THF) as a casting solvent, indicating immiscibility; on the other hand, samples using methyl chloride (MC) and cyclohexanone showed a single T g , indicating miscibility between the two polymers. The phase separation temperature for the miscible samples showed lower critical solution temperature type (LCST-type) behavior and reached its minimum when the content was about 70 mass% PMMA. Both the transmittance and haze of the miscible blended films were measured according to the American Standards Testing Method (ASTM) specification D1003. The transmittance for 6FDA-6FpDA/PMMA had a value of about 85% in the visual light range. However, 6FDA-6FpDA:DABA 2 : 1/PMMA showed a low transmittance below wavelengths of 550 nm. For haze, all of the films were clear with values of less than 1%. The mechanical scratch resistance was measured by pencil test (ASTM 3363). Increasing the 6FDA-6FpDA polyimide content was found to increase the scratch resistance of the films.