Effects of various polymer brushes on the crystallization of poly(ethylene glycol) in poly(ethylene glycol)-b-polystyrene and poly(ethylene glycol)-b-poly(methyl methacrylate) single crystals

The effects of PS and PMMA brushes on the crystallization of PEG in poly(ethylene glycol)-block-polystyrene (PEG-b-PS) and poly(ethylene glycol)-block-poly(methyl methacrylate) (PEG-b-PMMA) single crystals that have the same crystalline block molecular weight but different amorphous block molecular weights were investigated. The quality of the solvent (amyl acetate) employed and the interaction of the single-crystal substrate with the brush were found to influence the conformations of the PS and PMMA brushes, leading to more extended and packed pancake conformations, respectively. For PS and PMMA brushes with similar features, the conformation of the PMMA brushes led to a higher osmotic pressure on the substrate, so the substrate thickness was found to be significantly less than that seen when PS brushes were used. Even when the molecular weight of PMMA (M _n = 8,700 g/mol) is considerably lower than that of PS (M _n = 14,800 g/mol), the substrate in the presence of PMMA is thinner than that in the presence of PS (3.65 vs. 4.14 nm). Moreover, because there is less entropic repulsion between PS brushes than between PMMA brushes, the thickening of the substrate chains beneath them was more conspicuous when the crystallization temperature was increased.