The Effect of Hydrophobic Modification on Rheology and Structure of Hydrogen-Bonded Interpolymer Complexes of Polymethacrylic Acid (PMAA) and Poly(ethylene oxide) (PEO)

High Resolution Image Download MS PowerPoint Slide This study focuses on the effect of hydrophobic moieties on rheology and structure of hydrogen-bonded interpolymer complexes (IPCs) of different hydrophobically modified polymethacrylic acid (HM-PMAA) and poly(ethylene oxide) (PEO), where PMAA and PEO are known to form complexes with enhanced viscoelasticity at low pH due to H-bonding and chain entanglements. Dodecylamide and hexadecylamide modifications of 0 to ∼10 mol % were introduced into the PMAA chains. Using rheology, small-angle neutron scattering (SANS), and fluorescence spectroscopy, we examine how the additional hydrophobic interactions impact the properties of the polymer network. Our findings show that hydrophobic interaction leads to assembly processes that interfere mostly in an antagonistic way with this initial network structure. Fluorescence measurements confirm the presence of hydrophobic domains, and SANS demonstrates the formation of more compacted structures for C12 modification, while C16 modified systems have more of a tendency for interconnection. As the hydrophobic content increases, viscoelastic properties initially decrease, but a resurgence of viscoelasticity is observed at higher modification levels, particularly at low pH. This viscoelastic recovery is mostly seen for the dodecyl modification but hardly appears for the hexadecyl chains. In general, our findings show that hydrophobic modification of the polyelectrolyte allows for systematic control and tuning of the viscoelastic properties of these IPC hydrogels.