PLLA/PDLA blend films with only stereocomplex crystallites as a crystalline species together with pure PLLA and PDLA films with only homo‐crystallites as a crystalline species were prepared, and the effects of enantiomeric polymer blending, crystalline species, and crystallinity on the water vapor permeability were investigated. The WVT coefficient P of PLLA/PDLA blend films was 14–23% lower than that of pure PLLA and PDLA films in the crystallinity Xc range of 0–30%. Amorphous PLLA/PDLA blend films have a much lower P than pure PLLA and PDLA films. The dependence of P on Xc for blend films was stronger for Xc = 0–30% than for Xc = 30–100%. This dependence is discussed using the Nielsen model and the concept of “restricted” (or “restrained”) and “free” amorphous regions.

Cover: The image presents a permeation model of water vapor through a polylactide amorphous region, the stereocomplex crystal structure, and the helices of poly(L‐lactide) and poly(D‐lactide). Stereospecific strong interaction between enantiomeric poly(L‐lactide) and poly(D‐lactide), which can cause stereocomplexation, is found to be effective to increase the water vapor barrier property of polylactide‐based materials for a wide range of crystallinities. Further details can be found in the article by H. Tsuji* and T. Tsuruno .

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