Self-assembly through competitive interactions of miscible diblock copolymer/homopolymer blends:: Poly(vinylphenol-b-methyl methacrylate)/poly(vinylpyrrolidone) blend

We have investigated a new type A-b-B/C blend system, poly(vinylphenol-b-methyl methacrylate)/ poly(vinylpyrrolidone) (PVPh-b-PMMA)/PVP, where PVPh-b-PMMA block (A-b-B) copolymer, PVPh/PVP (A/C), and PMMA/PVP (B/C) blends are all miscible through hydrogen bond interaction or dipole-dipole, interaction. Because of the significantly stronger hydrogen bond interaction between PVPh and PVP than that between PVPh and PMMA, this miscible PVPh-b-PMMA copolymer becomes immiscible up on blending with 20-60 wt % PVP (27-56 wt % PMMA in the blend system) and can self-assemble to form ordered morphologies. Results from small-angle X-ray scattering (SAXS) and TEM consistently indicate that different compositions of PVPh-b-PMMA/PVP blends induce different microphase separation structures such as hexagonal and lamellar phases. However, sharp and multiple orders of diffraction are absent from the SAXS profiles, indicating relatively. limited sizes of the ordered domains. Large polydispersity in the molecular weight of PVP and small differences in the interaction parameters of the three components of PVPh, PMMA, and PVP are attributed to be the main reasons that limit the microphase separation in this blend system.