Crystallization and Melting of Poly(ethylene oxide) in Blends and Diblock Copolymers with Poly(methyl acrylate)

Blends of poly(ethylene oxide) (PEO) and poly(methyl acrylate) (PMA) as well as the respective diblock copolymers PEO-b-PMA form a homogeneous melt and undergo crystallization of PEO upon cooling. Although an identical PEO (Mn = 5000 g/mol) is used in blends and diblock copolymers, crystallization and melting behavior at comparable PMA contents differs strongly as revealed by temperature-resolved small-angle X-ray scattering (TR-SAXS) and differential scanning calorimetry (DSC) measurements. After isothermal crystallization, PEO lamellae in the blends thicken during heating from once-folded to extended chain crystals prior to melting as revealed by TR-SAXS. Contrarily, in PEO-b-PMA a thickening to extended chain lamellae is impossible when the PMA block exceeds an Mn of about 3000 g/mol. This behavior is caused by a balance between the tendency of the crystallizable block to form extended chain crystals, the tendency of the noncrystallizable chains to adopt a maximum in conformational entropy, and the spa...